pin 3 to pin 7 = 261 VAC
pin 3 to pin 1 =260 VAC
pin 3 to pin 8 = 260 VAC
pin 3 to B plus = 261 VAC
Line voltage is 115-120 AC so I don’t know what those readings mean except that they are not what I was expecting. The power transformer seems to be ok so I’m assuming if we can figure out why those voltages are high, then we’ll have plate voltages on all of the tubes....would appreciate any help.
Regards
PS: I couldn't find the schematic for this model no. but philco 41-245 is the same radio.
Not sure why you are referencing voltages to a plate of the 7Y4 pin 3. Try measuring for B+ voltage from pin 7 of the 7Y4 to chassis/ground. If there is voltage there then try on the other side of choke/speaker choke to chassis.
Radiodoc
**********
:Tube filament voltages are O.K. but I’m not reading any plate voltages on the tubes in this radio. Below are some readings I’m getting on the rectifier tube 7Y4:
:pin 3 to pin 7 = 261 VAC
:pin 3 to pin 1 =260 VAC
:pin 3 to pin 8 = 260 VAC
:pin 3 to B plus = 261 VAC
:
:Line voltage is 115-120 AC so I don’t know what those readings mean except that they are not what I was expecting. The power transformer seems to be ok so I’m assuming if we can figure out why those voltages are high, then we’ll have plate voltages on all of the tubes....would appreciate any help.
:Regards
:PS: I couldn't find the schematic for this model no. but philco 41-245 is the same radio.
Job
:Job,
:
:Not sure why you are referencing voltages to a plate of the 7Y4 pin 3. Try measuring for B+ voltage from pin 7 of the 7Y4 to chassis/ground. If there is voltage there then try on the other side of choke/speaker choke to chassis.
:
:Radiodoc
:**********
:
:
::Tube filament voltages are O.K. but I’m not reading any plate voltages on the tubes in this radio. Below are some readings I’m getting on the rectifier tube 7Y4:
::pin 3 to pin 7 = 261 VAC
::pin 3 to pin 1 =260 VAC
::pin 3 to pin 8 = 260 VAC
::pin 3 to B plus = 261 VAC
::
::Line voltage is 115-120 AC so I don’t know what those readings mean except that they are not what I was expecting. The power transformer seems to be ok so I’m assuming if we can figure out why those voltages are high, then we’ll have plate voltages on all of the tubes....would appreciate any help.
::Regards
::PS: I couldn't find the schematic for this model no. but philco 41-245 is the same radio.
Resistor 55 or 56 could be open? With either of these open you wouldn't read plate voltage.
Once past your rectifier tube measure voltage using the DC scale.
Norm
http://www.nostalgiaair.org/PagesByModel/404/M0013404.pdf
:Hi Doc----Some time back I thought I had seen a thread where it was suggested to take AC readings on rectifier tube from plate to cathode, etc....could be mistaken. Anyhow, I did not get any voltage from pin 7 to chassis/ground or other side of choke....What do this signify???....sounds serious to me?? Hopefully not power transformer.
:Job
:
:
::Job,
::
::Not sure why you are referencing voltages to a plate of the 7Y4 pin 3. Try measuring for B+ voltage from pin 7 of the 7Y4 to chassis/ground. If there is voltage there then try on the other side of choke/speaker choke to chassis.
::
::Radiodoc
::**********
::
::
:::Tube filament voltages are O.K. but I’m not reading any plate voltages on the tubes in this radio. Below are some readings I’m getting on the rectifier tube 7Y4:
:::pin 3 to pin 7 = 261 VAC
:::pin 3 to pin 1 =260 VAC
:::pin 3 to pin 8 = 260 VAC
:::pin 3 to B plus = 261 VAC
:::
:::Line voltage is 115-120 AC so I don’t know what those readings mean except that they are not what I was expecting. The power transformer seems to be ok so I’m assuming if we can figure out why those voltages are high, then we’ll have plate voltages on all of the tubes....would appreciate any help.
:::Regards
:::PS: I couldn't find the schematic for this model no. but philco 41-245 is the same radio.
Looks like a 7Y4 with a detached cathode. What am I missing?
If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
Best Regards,
Bill Grimm
Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
Norm
:Hi Guys,
: Looks like a 7Y4 with a detached cathode. What am I missing?
: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
:
:Best Regards,
:
:Bill Grimm
:
: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:
:Norm
:
::Hi Guys,
:: Looks like a 7Y4 with a detached cathode. What am I missing?
:: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::
::Best Regards,
::
::Bill Grimm
Hi Norm,
I agree. That will do it, too.
All the Best,
Bill
Regards
::Hi Bill
::
:: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
::
::Norm
::
:::Hi Guys,
::: Looks like a 7Y4 with a detached cathode. What am I missing?
::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
:::
:::Best Regards,
:::
:::Bill Grimm
:Hi Norm,
: I agree. That will do it, too.
:
:All the Best,
:
:Bill
You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
Norm
:Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
:Regards
:
:
:
:::Hi Bill
:::
::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:::
:::Norm
:::
::::Hi Guys,
:::: Looks like a 7Y4 with a detached cathode. What am I missing?
:::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::::
::::Best Regards,
::::
::::Bill Grimm
::Hi Norm,
:: I agree. That will do it, too.
::
::All the Best,
::
::Bill
:
: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
:
:Norm
:
::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
::Regards
::
::
::
::::Hi Bill
::::
:::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
::::
::::Norm
::::
:::::Hi Guys,
::::: Looks like a 7Y4 with a detached cathode. What am I missing?
::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
:::::
:::::Best Regards,
:::::
:::::Bill Grimm
:::Hi Norm,
::: I agree. That will do it, too.
:::
:::All the Best,
:::
:::Bill
Hi Job and Norm,
Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
All the Best,
Bill Grimm
Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
Radiodoc
**********
::Hi Job
::
:: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
::
::Norm
::
:::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
:::Regards
:::
:::
:::
:::::Hi Bill
:::::
::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:::::
:::::Norm
:::::
::::::Hi Guys,
:::::: Looks like a 7Y4 with a detached cathode. What am I missing?
:::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::::::
::::::Best Regards,
::::::
::::::Bill Grimm
::::Hi Norm,
:::: I agree. That will do it, too.
::::
::::All the Best,
::::
::::Bill
:Hi Job and Norm,
: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
:
:All the Best,
:
:Bill Grimm
Bill
:Job,
:
:Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
:
:Radiodoc
:**********
:
:
:::Hi Job
:::
::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
:::
:::Norm
:::
::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
::::Regards
::::
::::
::::
::::::Hi Bill
::::::
:::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
::::::
::::::Norm
::::::
:::::::Hi Guys,
::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
:::::::
:::::::Best Regards,
:::::::
:::::::Bill Grimm
:::::Hi Norm,
::::: I agree. That will do it, too.
:::::
:::::All the Best,
:::::
:::::Bill
::Hi Job and Norm,
:: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
::
::All the Best,
::
::Bill Grimm
Regards
:Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
:
:Bill
:
::Job,
::
::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
::
::Radiodoc
::**********
::
::
::::Hi Job
::::
:::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
::::
::::Norm
::::
:::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
:::::Regards
:::::
:::::
:::::
:::::::Hi Bill
:::::::
::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:::::::
:::::::Norm
:::::::
::::::::Hi Guys,
:::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
:::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::::::::
::::::::Best Regards,
::::::::
::::::::Bill Grimm
::::::Hi Norm,
:::::: I agree. That will do it, too.
::::::
::::::All the Best,
::::::
::::::Bill
:::Hi Job and Norm,
::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
:::
:::All the Best,
:::
:::Bill Grimm
Hi Job,
The center tap of the HV winding goes to the negative of ecap57. That is what the schematic tells me. Often the center tap doesn't go to ground, but through a voltage divider. This creates the bias for the 7B5.
The negative needs to connect to the 220 ohm resistor (56) of a voltage divider, and the 1 meg (49)grid resistor of the 7B5, as well as the electrolytic (57). Note the negative voltage finally gets to ground through the 68 ohm resistor (55) connected to the other side of the 220 ohm resistor (56). This is a common arrangement. Zenith would have put the field coil there, but that is another story.
Your problem seems to have been not getting the negative to the ground. You should be able to trace it to the ground now.
Best Regards,
Bill Grimm
:
:Hi Job,
: The center tap of the HV winding goes to the negative of ecap57. That is what the schematic tells me. Often the center tap doesn't go to ground, but through a voltage divider. This creates the bias for the 7B5.
: The negative needs to connect to the 220 ohm resistor (56) of a voltage divider, and the 1 meg (49)grid resistor of the 7B5, as well as the electrolytic (57). Note the negative voltage finally gets to ground through the 68 ohm resistor (55) connected to the other side of the 220 ohm resistor (56). This is a common arrangement. Zenith would have put the field coil there, but that is another story.
: Your problem seems to have been not getting the negative to the ground. You should be able to trace it to the ground now.
:
:Best Regards,
:
:Bill Grimm
Job,
If your radio is truly a 41-245, the pictoral of the underside of the chassis shows resistors 55 & 56 are mounted on a terminal strip just in front of the 7B5 and 7Y4 sockets.
Radiodoc
**********
::
::Hi Job,
:: The center tap of the HV winding goes to the negative of ecap57. That is what the schematic tells me. Often the center tap doesn't go to ground, but through a voltage divider. This creates the bias for the 7B5.
:: The negative needs to connect to the 220 ohm resistor (56) of a voltage divider, and the 1 meg (49)grid resistor of the 7B5, as well as the electrolytic (57). Note the negative voltage finally gets to ground through the 68 ohm resistor (55) connected to the other side of the 220 ohm resistor (56). This is a common arrangement. Zenith would have put the field coil there, but that is another story.
:: Your problem seems to have been not getting the negative to the ground. You should be able to trace it to the ground now.
::
::Best Regards,
::
::Bill Grimm
:
:Job,
:
:If your radio is truly a 41-245, the pictoral of the underside of the chassis shows resistors 55 & 56 are mounted on a terminal strip just in front of the 7B5 and 7Y4 sockets.
:
:Radiodoc
:**********
:
Doc------Thanks for the email with the schematic showing the routing of the B+ voltage. I have done a complete resistance check on this radio and all readings are in satisfactory range. Resistors are fine and I don’t know of anything else to check. The power transformer is giving off voltage as per the following AC readings from different points in the rectifier tube, so that seems to be performing ok......I’ll let you gentlemen interpret those readings but it probably just means that the power supply section is fine:
Rectifier tube 7Y4
pin 1(f) to pin 8(f)---------5.8 Vac
pin 3(a’) to B+--------------261 Vac
pin 3(a’) to pin 6(a”)-------551 Vac
pin 3(a’) to pin 1(f)--------260 Vac
pin 3(a’) to pin 8(f)--------260 Vac
pin 6(a”) to pin 1 (f)-------280 Vac
pin 6 (a”) to pin 8 (f)------277 Vac
pin 7 (cathode) to pin 3 (a’)--261 Vac
pin 7 (cathode) to pin 6 (a”)--277 Vac
I tested all of the tubes in this radio with a tube tester and they tested ok so I’m puzzled as to where to go from here.
Regards
:::
:::Hi Job,
::: The center tap of the HV winding goes to the negative of ecap57. That is what the schematic tells me. Often the center tap doesn't go to ground, but through a voltage divider. This creates the bias for the 7B5.
::: The negative needs to connect to the 220 ohm resistor (56) of a voltage divider, and the 1 meg (49)grid resistor of the 7B5, as well as the electrolytic (57). Note the negative voltage finally gets to ground through the 68 ohm resistor (55) connected to the other side of the 220 ohm resistor (56). This is a common arrangement. Zenith would have put the field coil there, but that is another story.
::: Your problem seems to have been not getting the negative to the ground. You should be able to trace it to the ground now.
:::
:::Best Regards,
:::
:::Bill Grimm
::
::Job,
::
::If your radio is truly a 41-245, the pictoral of the underside of the chassis shows resistors 55 & 56 are mounted on a terminal strip just in front of the 7B5 and 7Y4 sockets.
::
::Radiodoc
::**********
::
:
:
:Doc------Thanks for the email with the schematic showing the routing of the B+ voltage. I have done a complete resistance check on this radio and all readings are in satisfactory range. Resistors are fine and I don’t know of anything else to check. The power transformer is giving off voltage as per the following AC readings from different points in the rectifier tube, so that seems to be performing ok......I’ll let you gentlemen interpret those readings but it probably just means that the power supply section is fine:
:
:Rectifier tube 7Y4
:
:pin 1(f) to pin 8(f)---------5.8 Vac
:pin 3(a’) to B+--------------261 Vac
:pin 3(a’) to pin 6(a”)-------551 Vac
:pin 3(a’) to pin 1(f)--------260 Vac
:pin 3(a’) to pin 8(f)--------260 Vac
:pin 6(a”) to pin 1 (f)-------280 Vac
:pin 6 (a”) to pin 8 (f)------277 Vac
:pin 7 (cathode) to pin 3 (a’)--261 Vac
:pin 7 (cathode) to pin 6 (a”)--277 Vac
:
:I tested all of the tubes in this radio with a tube tester and they tested ok so I’m puzzled as to where to go from here.
:
:Regards
Job,
What is the DC voltage (meter set to measure DC voltage) from pin 7 (cathode) of the 7Y4 to chassis/ground? There has to be B+ voltage there else there will not be voltage to the rest of the radio.
Radiodoc
**********
Bill
:Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
:Regards
:
:
:
::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
::
::Bill
::
:::Job,
:::
:::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
:::
:::Radiodoc
:::**********
:::
:::
:::::Hi Job
:::::
::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
:::::
:::::Norm
:::::
::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
::::::Regards
::::::
::::::
::::::
::::::::Hi Bill
::::::::
:::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
::::::::
::::::::Norm
::::::::
:::::::::Hi Guys,
::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
:::::::::
:::::::::Best Regards,
:::::::::
:::::::::Bill Grimm
:::::::Hi Norm,
::::::: I agree. That will do it, too.
:::::::
:::::::All the Best,
:::::::
:::::::Bill
::::Hi Job and Norm,
:::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
::::
::::All the Best,
::::
::::Bill Grimm
Regards
:Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
:Bill
:
::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
::Regards
::
::
::
:::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
:::
:::Bill
:::
::::Job,
::::
::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
::::
::::Radiodoc
::::**********
::::
::::
::::::Hi Job
::::::
:::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
::::::
::::::Norm
::::::
:::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
:::::::Regards
:::::::
:::::::
:::::::
:::::::::Hi Bill
:::::::::
::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:::::::::
:::::::::Norm
:::::::::
::::::::::Hi Guys,
:::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
:::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::::::::::
::::::::::Best Regards,
::::::::::
::::::::::Bill Grimm
::::::::Hi Norm,
:::::::: I agree. That will do it, too.
::::::::
::::::::All the Best,
::::::::
::::::::Bill
:::::Hi Job and Norm,
::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
:::::
:::::All the Best,
:::::
:::::Bill Grimm
I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
Regards
:Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
:Regards
:
:
:
::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
::Bill
::
:::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
:::Regards
:::
:::
:::
::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
::::
::::Bill
::::
:::::Job,
:::::
:::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
:::::
:::::Radiodoc
:::::**********
:::::
:::::
:::::::Hi Job
:::::::
::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
:::::::
:::::::Norm
:::::::
::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
::::::::Regards
::::::::
::::::::
::::::::
::::::::::Hi Bill
::::::::::
:::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
::::::::::
::::::::::Norm
::::::::::
:::::::::::Hi Guys,
::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
:::::::::::
:::::::::::Best Regards,
:::::::::::
:::::::::::Bill Grimm
:::::::::Hi Norm,
::::::::: I agree. That will do it, too.
:::::::::
:::::::::All the Best,
:::::::::
:::::::::Bill
::::::Hi Job and Norm,
:::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
::::::
::::::All the Best,
::::::
::::::Bill Grimm
One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
Radiodoc
**********
:Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
:I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
:Regards
:
:
:
:
::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
::Regards
::
::
::
:::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
:::Bill
:::
::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
::::Regards
::::
::::
::::
:::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
:::::
:::::Bill
:::::
::::::Job,
::::::
::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
::::::
::::::Radiodoc
::::::**********
::::::
::::::
::::::::Hi Job
::::::::
:::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
::::::::
::::::::Norm
::::::::
:::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
:::::::::Regards
:::::::::
:::::::::
:::::::::
:::::::::::Hi Bill
:::::::::::
::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:::::::::::
:::::::::::Norm
:::::::::::
::::::::::::Hi Guys,
:::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
:::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::::::::::::
::::::::::::Best Regards,
::::::::::::
::::::::::::Bill Grimm
::::::::::Hi Norm,
:::::::::: I agree. That will do it, too.
::::::::::
::::::::::All the Best,
::::::::::
::::::::::Bill
:::::::Hi Job and Norm,
::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
:::::::
:::::::All the Best,
:::::::
:::::::Bill Grimm
:
:One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
:
:Radiodoc
:**********
Job,
One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
Radiodoc
**********
:
:
::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
::Regards
::
::
::
::
:::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
:::Regards
:::
:::
:::
::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
::::Bill
::::
:::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
:::::Regards
:::::
:::::
:::::
::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
::::::
::::::Bill
::::::
:::::::Job,
:::::::
:::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
:::::::
:::::::Radiodoc
:::::::**********
:::::::
:::::::
:::::::::Hi Job
:::::::::
::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
:::::::::
:::::::::Norm
:::::::::
::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
::::::::::Regards
::::::::::
::::::::::
::::::::::
::::::::::::Hi Bill
::::::::::::
:::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
::::::::::::
::::::::::::Norm
::::::::::::
:::::::::::::Hi Guys,
::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
:::::::::::::
:::::::::::::Best Regards,
:::::::::::::
:::::::::::::Bill Grimm
:::::::::::Hi Norm,
::::::::::: I agree. That will do it, too.
:::::::::::
:::::::::::All the Best,
:::::::::::
:::::::::::Bill
::::::::Hi Job and Norm,
:::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
::::::::
::::::::All the Best,
::::::::
::::::::Bill Grimm
Don't give up there are only a few things that can prevent DC voltage on pin #7 of your 7Y4. At one point the 7Y4 was tested good but you could try silicon diodes in place of the tube.
Measure center tap of the high voltage transformer winding to chassis. Should have low resistance, around 300 ohms.
If the first filter cap is open voltage might be very low but still should read something.
Be sure filament pins (1, 8) make good contact on the 7Y4 so it's lit.
This should be all it takes to have DC voltage.
Norm
::Job,
::
::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
::
::Radiodoc
::**********
:Job,
:
:One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
:
:Radiodoc
:**********
:
:
::
::
:::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
:::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
:::Regards
:::
:::
:::
:::
::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
::::Regards
::::
::::
::::
:::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
:::::Bill
:::::
::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
::::::Regards
::::::
::::::
::::::
:::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
:::::::
:::::::Bill
:::::::
::::::::Job,
::::::::
::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
::::::::
::::::::Radiodoc
::::::::**********
::::::::
::::::::
::::::::::Hi Job
::::::::::
:::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
::::::::::
::::::::::Norm
::::::::::
:::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
:::::::::::Regards
:::::::::::
:::::::::::
:::::::::::
:::::::::::::Hi Bill
:::::::::::::
::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:::::::::::::
:::::::::::::Norm
:::::::::::::
::::::::::::::Hi Guys,
:::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
:::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::::::::::::::
::::::::::::::Best Regards,
::::::::::::::
::::::::::::::Bill Grimm
::::::::::::Hi Norm,
:::::::::::: I agree. That will do it, too.
::::::::::::
::::::::::::All the Best,
::::::::::::
::::::::::::Bill
:::::::::Hi Job and Norm,
::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
:::::::::
:::::::::All the Best,
:::::::::
:::::::::Bill Grimm
BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
Confirm that I did send you additionals / surplus at that time.
BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
73's de Edd
::Job,
::
::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
::
::Radiodoc
::**********
:Job,
:
:One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
:
:Radiodoc
:**********
:
:
::
::
:::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
:::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
:::Regards
:::
:::
:::
:::
::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
::::Regards
::::
::::
::::
:::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
:::::Bill
:::::
::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
::::::Regards
::::::
::::::
::::::
:::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
:::::::
:::::::Bill
:::::::
::::::::Job,
::::::::
::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
::::::::
::::::::Radiodoc
::::::::**********
::::::::
::::::::
::::::::::Hi Job
::::::::::
:::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
::::::::::
::::::::::Norm
::::::::::
:::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
:::::::::::Regards
:::::::::::
:::::::::::
:::::::::::
:::::::::::::Hi Bill
:::::::::::::
::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:::::::::::::
:::::::::::::Norm
:::::::::::::
::::::::::::::Hi Guys,
:::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
:::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::::::::::::::
::::::::::::::Best Regards,
::::::::::::::
::::::::::::::Bill Grimm
::::::::::::Hi Norm,
:::::::::::: I agree. That will do it, too.
::::::::::::
::::::::::::All the Best,
::::::::::::
::::::::::::Bill
:::::::::Hi Job and Norm,
::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
:::::::::
:::::::::All the Best,
:::::::::
:::::::::Bill Grimm
I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
Regards
:
:
:
:
:BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
:
:Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
:
:I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
:
:Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
:Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
:Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
:
:I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
:
:Confirm that I did send you additionals / surplus at that time.
:
:BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
:
:BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
:
:
:
:73's de Edd
:
:
:
:
:
:
:
:
:::Job,
:::
:::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
:::
:::Radiodoc
:::**********
::Job,
::
::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
::
::Radiodoc
::**********
::
::
:::
:::
::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
::::Regards
::::
::::
::::
::::
:::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
:::::Regards
:::::
:::::
:::::
::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
::::::Bill
::::::
:::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
:::::::Regards
:::::::
:::::::
:::::::
::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
::::::::
::::::::Bill
::::::::
:::::::::Job,
:::::::::
:::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
:::::::::
:::::::::Radiodoc
:::::::::**********
:::::::::
:::::::::
:::::::::::Hi Job
:::::::::::
::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
:::::::::::
:::::::::::Norm
:::::::::::
::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
::::::::::::Regards
::::::::::::
::::::::::::
::::::::::::
::::::::::::::Hi Bill
::::::::::::::
:::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
::::::::::::::
::::::::::::::Norm
::::::::::::::
:::::::::::::::Hi Guys,
::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
:::::::::::::::
:::::::::::::::Best Regards,
:::::::::::::::
:::::::::::::::Bill Grimm
:::::::::::::Hi Norm,
::::::::::::: I agree. That will do it, too.
:::::::::::::
:::::::::::::All the Best,
:::::::::::::
:::::::::::::Bill
::::::::::Hi Job and Norm,
:::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
::::::::::
::::::::::All the Best,
::::::::::
::::::::::Bill Grimm
Although 6X4 is electrically similar it requires a different socket. 6X4 is miniature, 7Y4 loctal.
Norm
:Ok gentlemen, let's see where we are. First, I measured center tap of HVT winding to chassis (B Minus) and got a reading of 296 ohms. However, after I had completed more testing, etc. I rechecked and couldn't get a reading...out of scale range..STRANGE..
:I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
:Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
:Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
:Regards
:
:
::
::
::
::
::BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
::
::Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
::
::I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
:: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
::
::Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
::Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
::Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
::
::I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
::
::Confirm that I did send you additionals / surplus at that time.
::
::BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
::
::BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
::
::
::
::73's de Edd
::
::
::
::
::
::
::
::
::::Job,
::::
::::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
::::
::::Radiodoc
::::**********
:::Job,
:::
:::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
:::
:::Radiodoc
:::**********
:::
:::
::::
::::
:::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
:::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
:::::Regards
:::::
:::::
:::::
:::::
::::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
::::::Regards
::::::
::::::
::::::
:::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
:::::::Bill
:::::::
::::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
::::::::Regards
::::::::
::::::::
::::::::
:::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
:::::::::
:::::::::Bill
:::::::::
::::::::::Job,
::::::::::
::::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
::::::::::
::::::::::Radiodoc
::::::::::**********
::::::::::
::::::::::
::::::::::::Hi Job
::::::::::::
:::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
::::::::::::
::::::::::::Norm
::::::::::::
:::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
:::::::::::::Regards
:::::::::::::
:::::::::::::
:::::::::::::
:::::::::::::::Hi Bill
:::::::::::::::
::::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:::::::::::::::
:::::::::::::::Norm
:::::::::::::::
::::::::::::::::Hi Guys,
:::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
:::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::::::::::::::::
::::::::::::::::Best Regards,
::::::::::::::::
::::::::::::::::Bill Grimm
::::::::::::::Hi Norm,
:::::::::::::: I agree. That will do it, too.
::::::::::::::
::::::::::::::All the Best,
::::::::::::::
::::::::::::::Bill
:::::::::::Hi Job and Norm,
::::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
:::::::::::
:::::::::::All the Best,
:::::::::::
:::::::::::Bill Grimm
OHH-TAYYY…it looks like we do be OK on that point where the center tap wire connects to the external circuitry and that you are confirming the
presence of the combined resistance of #55 and #56 Voltage divider resistor pair.
BUT what specific info needed was the resistance read out between the Yellow- Green CT connection and both / either of the Green wires of the HV windings.
With what info you supplied at the last…that floating / blinking display is indicative of an open circuit.....instead of the desired ~300 ohms.
That then suggests that you might leave the ohmmic metering clip connected between the Yellow- Green CT lead and then take your choice of one of the outer Green HV sec wires to connect other metering wire and then get a hold of the green white wire at the entry point to the T-former and enact a pressing inwards of the wire and then a slight pull on the wire to see if any continuity is intermittently shown on metering. If no results , then the loosening of the 2-4 screws and dropping of the bell covers of the T-former might be in order, to then visually inspect the green white wiring connection and its routing at the sides of the winding..at least we know that the total series connection is made….. but just possibly an open connection having developed at that Green- White CT wire connection.
I just might have given you some dupes on the Zeners, from the tolerance respect…I do think that one unit sent was a special precision voltage reference…1N823B with a .005 % reg tolerance… but Zeners are not of the family of diodes which we speak.
The units of interest would have been black epoxy molded casings , with 1N4007 marked lengthwise on the side.
73's de Edd
:Ok gentlemen, let's see where we are. First, I measured center tap of HVT winding to chassis (B Minus) and got a reading of 296 ohms. However, after I had completed more testing, etc. I rechecked and couldn't get a reading...out of scale range..STRANGE..
:I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
:Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
:Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
:Regards
:
:
::
::
::
::
::BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
::
::Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
::
::I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
:: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
::
::Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
::Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
::Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
::
::I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
::
::Confirm that I did send you additionals / surplus at that time.
::
::BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
::
::BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
::
::
::
::73's de Edd
::
::
::
::
::
::
::
::
::::Job,
::::
::::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
::::
::::Radiodoc
::::**********
:::Job,
:::
:::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
:::
:::Radiodoc
:::**********
:::
:::
::::
::::
:::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
:::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
:::::Regards
:::::
:::::
:::::
:::::
::::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
::::::Regards
::::::
::::::
::::::
:::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
:::::::Bill
:::::::
::::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
::::::::Regards
::::::::
::::::::
::::::::
:::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
:::::::::
:::::::::Bill
:::::::::
::::::::::Job,
::::::::::
::::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
::::::::::
::::::::::Radiodoc
::::::::::**********
::::::::::
::::::::::
::::::::::::Hi Job
::::::::::::
:::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
::::::::::::
::::::::::::Norm
::::::::::::
:::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
:::::::::::::Regards
:::::::::::::
:::::::::::::
:::::::::::::
:::::::::::::::Hi Bill
:::::::::::::::
::::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:::::::::::::::
:::::::::::::::Norm
:::::::::::::::
::::::::::::::::Hi Guys,
:::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
:::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::::::::::::::::
::::::::::::::::Best Regards,
::::::::::::::::
::::::::::::::::Bill Grimm
::::::::::::::Hi Norm,
:::::::::::::: I agree. That will do it, too.
::::::::::::::
::::::::::::::All the Best,
::::::::::::::
::::::::::::::Bill
:::::::::::Hi Job and Norm,
::::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
:::::::::::
:::::::::::All the Best,
:::::::::::
:::::::::::Bill Grimm
:
:
:
:
:
:OHH-TAYYY…it looks like we do be OK on that point where the center tap wire connects to the external circuitry and that you are confirming the
:presence of the combined resistance of #55 and #56 Voltage divider resistor pair.
:BUT what specific info needed was the resistance read out between the Yellow- Green CT connection and both / either of the Green wires of the HV windings.
:
:With what info you supplied at the last…that floating / blinking display is indicative of an open circuit.....instead of the desired ~300 ohms.
:
:That then suggests that you might leave the ohmmic metering clip connected between the Yellow- Green CT lead and then take your choice of one of the outer Green HV sec wires to connect other metering wire and then get a hold of the green white wire at the entry point to the T-former and enact a pressing inwards of the wire and then a slight pull on the wire to see if any continuity is intermittently shown on metering. If no results , then the loosening of the 2-4 screws and dropping of the bell covers of the T-former might be in order, to then visually inspect the green white wiring connection and its routing at the sides of the winding..at least we know that the total series connection is made….. but just possibly an open connection having developed at that Green- White CT wire connection.
:
:I just might have given you some dupes on the Zeners, from the tolerance respect…I do think that one unit sent was a special precision voltage reference…1N823B with a .005 % reg tolerance… but Zeners are not of the family of diodes which we speak.
:The units of interest would have been black epoxy molded casings , with 1N4007 marked lengthwise on the side.
:
:Addenda: just now caught the :
"I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively."...but check for possible intermittency of connectivity. Then with CT connection being solid, I guess the 4007 would be next. ( Or the temporary hay-wiring in of the 5 wires, 7 pin mini socket and in stock 6X4 might be in order)
:
:
:73's de Edd
:
:
:
:
:
:
:
::Ok gentlemen, let's see where we are. First, I measured center tap of HVT winding to chassis (B Minus) and got a reading of 296 ohms. However, after I had completed more testing, etc. I rechecked and couldn't get a reading...out of scale range..STRANGE..
::I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
::Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
::Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
::Regards
::
::
:::
:::
:::
:::
:::BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
:::
:::Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
:::
:::I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
::: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
:::
:::Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
:::Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
:::Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
:::
:::I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
:::
:::Confirm that I did send you additionals / surplus at that time.
:::
:::BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
:::
:::BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
:::
:::
:::
:::73's de Edd
:::
:::
:::
:::
:::
:::
:::
:::
:::::Job,
:::::
:::::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
:::::
:::::Radiodoc
:::::**********
::::Job,
::::
::::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
::::
::::Radiodoc
::::**********
::::
::::
:::::
:::::
::::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
::::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
::::::Regards
::::::
::::::
::::::
::::::
:::::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
:::::::Regards
:::::::
:::::::
:::::::
::::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
::::::::Bill
::::::::
:::::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
:::::::::Regards
:::::::::
:::::::::
:::::::::
::::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
::::::::::
::::::::::Bill
::::::::::
:::::::::::Job,
:::::::::::
:::::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
:::::::::::
:::::::::::Radiodoc
:::::::::::**********
:::::::::::
:::::::::::
:::::::::::::Hi Job
:::::::::::::
::::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
:::::::::::::
:::::::::::::Norm
:::::::::::::
::::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
::::::::::::::Regards
::::::::::::::
::::::::::::::
::::::::::::::
::::::::::::::::Hi Bill
::::::::::::::::
:::::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
::::::::::::::::
::::::::::::::::Norm
::::::::::::::::
:::::::::::::::::Hi Guys,
::::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
::::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
:::::::::::::::::
:::::::::::::::::Best Regards,
:::::::::::::::::
:::::::::::::::::Bill Grimm
:::::::::::::::Hi Norm,
::::::::::::::: I agree. That will do it, too.
:::::::::::::::
:::::::::::::::All the Best,
:::::::::::::::
:::::::::::::::Bill
::::::::::::Hi Job and Norm,
:::::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
::::::::::::
::::::::::::All the Best,
::::::::::::
::::::::::::Bill Grimm
I notice there are further instructions so I’ll check them out.
::
::
::
::OHH-TAYYY…it looks like we do be OK on that point where the center tap wire connects to the external circuitry and that you are confirming the
::presence of the combined resistance of #55 and #56 Voltage divider resistor pair.
::BUT what specific info needed was the resistance read out between the Yellow- Green CT connection and both / either of the Green wires of the HV windings.
::
::With what info you supplied at the last…that floating / blinking display is indicative of an open circuit.....instead of the desired ~300 ohms.
::
::That then suggests that you might leave the ohmmic metering clip connected between the Yellow- Green CT lead and then take your choice of one of the outer Green HV sec wires to connect other metering wire and then get a hold of the green white wire at the entry point to the T-former and enact a pressing inwards of the wire and then a slight pull on the wire to see if any continuity is intermittently shown on metering. If no results , then the loosening of the 2-4 screws and dropping of the bell covers of the T-former might be in order, to then visually inspect the green white wiring connection and its routing at the sides of the winding..at least we know that the total series connection is made….. but just possibly an open connection having developed at that Green- White CT wire connection.
::
::I just might have given you some dupes on the Zeners, from the tolerance respect…I do think that one unit sent was a special precision voltage reference…1N823B with a .005 % reg tolerance… but Zeners are not of the family of diodes which we speak.
::The units of interest would have been black epoxy molded casings , with 1N4007 marked lengthwise on the side.
::
::Addenda: just now caught the :
:"I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively."...but check for possible intermittency of connectivity. Then with CT connection being solid, I guess the 4007 would be next. ( Or the temporary hay-wiring in of the 5 wires, 7 pin mini socket and in stock 6X4 might be in order)
::
::
::73's de Edd
::
::
::
::
::
::
::
:::Ok gentlemen, let's see where we are. First, I measured center tap of HVT winding to chassis (B Minus) and got a reading of 296 ohms. However, after I had completed more testing, etc. I rechecked and couldn't get a reading...out of scale range..STRANGE..
:::I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
:::Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
:::Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
:::Regards
:::
:::
::::
::::
::::
::::
::::BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
::::
::::Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
::::
::::I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
:::: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
::::
::::Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
::::Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
::::Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
::::
::::I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
::::
::::Confirm that I did send you additionals / surplus at that time.
::::
::::BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
::::
::::BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
::::
::::
::::
::::73's de Edd
::::
::::
::::
::::
::::
::::
::::
::::
::::::Job,
::::::
::::::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
::::::
::::::Radiodoc
::::::**********
:::::Job,
:::::
:::::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
:::::
:::::Radiodoc
:::::**********
:::::
:::::
::::::
::::::
:::::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
:::::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
:::::::Regards
:::::::
:::::::
:::::::
:::::::
::::::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
::::::::Regards
::::::::
::::::::
::::::::
:::::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
:::::::::Bill
:::::::::
::::::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
::::::::::Regards
::::::::::
::::::::::
::::::::::
:::::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
:::::::::::
:::::::::::Bill
:::::::::::
::::::::::::Job,
::::::::::::
::::::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
::::::::::::
::::::::::::Radiodoc
::::::::::::**********
::::::::::::
::::::::::::
::::::::::::::Hi Job
::::::::::::::
:::::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
::::::::::::::
::::::::::::::Norm
::::::::::::::
:::::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
:::::::::::::::Regards
:::::::::::::::
:::::::::::::::
:::::::::::::::
:::::::::::::::::Hi Bill
:::::::::::::::::
::::::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:::::::::::::::::
:::::::::::::::::Norm
:::::::::::::::::
::::::::::::::::::Hi Guys,
:::::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
:::::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::::::::::::::::::
::::::::::::::::::Best Regards,
::::::::::::::::::
::::::::::::::::::Bill Grimm
::::::::::::::::Hi Norm,
:::::::::::::::: I agree. That will do it, too.
::::::::::::::::
::::::::::::::::All the Best,
::::::::::::::::
::::::::::::::::Bill
:::::::::::::Hi Job and Norm,
::::::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
:::::::::::::
:::::::::::::All the Best,
:::::::::::::
:::::::::::::Bill Grimm
Just one more thing: As Norm Leal mentioned in an earlier post, did you visually confirm the filament was lighting in the 7Y4 tube. I worked on Motorola communications equipment back when and the loctal tube sockets were a source of headaches for me by losing contact between the socket and tube pins.
Radiodoc
**********
:OK Gentlemen-----I carried out the test to determine if there was DC voltage on anodes of tube 7Y4 as per instructions. Edd, I used one of those little black suckers that you sent and I did receive lots of voltage on the anodes when scraching them. So, do we now assume that tube 7Y4 if ok??? Norm, I guess that the 6X4 tube won’t be any good after all but hopefully the 7Y4 will be ok.
:I notice there are further instructions so I’ll check them out.
:
:
:
:
:::
:::
:::
:::OHH-TAYYY…it looks like we do be OK on that point where the center tap wire connects to the external circuitry and that you are confirming the
:::presence of the combined resistance of #55 and #56 Voltage divider resistor pair.
:::BUT what specific info needed was the resistance read out between the Yellow- Green CT connection and both / either of the Green wires of the HV windings.
:::
:::With what info you supplied at the last…that floating / blinking display is indicative of an open circuit.....instead of the desired ~300 ohms.
:::
:::That then suggests that you might leave the ohmmic metering clip connected between the Yellow- Green CT lead and then take your choice of one of the outer Green HV sec wires to connect other metering wire and then get a hold of the green white wire at the entry point to the T-former and enact a pressing inwards of the wire and then a slight pull on the wire to see if any continuity is intermittently shown on metering. If no results , then the loosening of the 2-4 screws and dropping of the bell covers of the T-former might be in order, to then visually inspect the green white wiring connection and its routing at the sides of the winding..at least we know that the total series connection is made….. but just possibly an open connection having developed at that Green- White CT wire connection.
:::
:::I just might have given you some dupes on the Zeners, from the tolerance respect…I do think that one unit sent was a special precision voltage reference…1N823B with a .005 % reg tolerance… but Zeners are not of the family of diodes which we speak.
:::The units of interest would have been black epoxy molded casings , with 1N4007 marked lengthwise on the side.
:::
:::Addenda: just now caught the :
::"I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively."...but check for possible intermittency of connectivity. Then with CT connection being solid, I guess the 4007 would be next. ( Or the temporary hay-wiring in of the 5 wires, 7 pin mini socket and in stock 6X4 might be in order)
:::
:::
:::73's de Edd
:::
:::
:::
:::
:::
:::
:::
::::Ok gentlemen, let's see where we are. First, I measured center tap of HVT winding to chassis (B Minus) and got a reading of 296 ohms. However, after I had completed more testing, etc. I rechecked and couldn't get a reading...out of scale range..STRANGE..
::::I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
::::Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
::::Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
::::Regards
::::
::::
:::::
:::::
:::::
:::::
:::::BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
:::::
:::::Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
:::::
:::::I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
::::: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
:::::
:::::Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
:::::Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
:::::Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
:::::
:::::I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
:::::
:::::Confirm that I did send you additionals / surplus at that time.
:::::
:::::BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
:::::
:::::BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
:::::
:::::
:::::
:::::73's de Edd
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::::Job,
:::::::
:::::::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
:::::::
:::::::Radiodoc
:::::::**********
::::::Job,
::::::
::::::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
::::::
::::::Radiodoc
::::::**********
::::::
::::::
:::::::
:::::::
::::::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
::::::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
::::::::Regards
::::::::
::::::::
::::::::
::::::::
:::::::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
:::::::::Regards
:::::::::
:::::::::
:::::::::
::::::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
::::::::::Bill
::::::::::
:::::::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
:::::::::::Regards
:::::::::::
:::::::::::
:::::::::::
::::::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
::::::::::::
::::::::::::Bill
::::::::::::
:::::::::::::Job,
:::::::::::::
:::::::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
:::::::::::::
:::::::::::::Radiodoc
:::::::::::::**********
:::::::::::::
:::::::::::::
:::::::::::::::Hi Job
:::::::::::::::
::::::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
:::::::::::::::
:::::::::::::::Norm
:::::::::::::::
::::::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
::::::::::::::::Regards
::::::::::::::::
::::::::::::::::
::::::::::::::::
::::::::::::::::::Hi Bill
::::::::::::::::::
:::::::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
::::::::::::::::::
::::::::::::::::::Norm
::::::::::::::::::
:::::::::::::::::::Hi Guys,
::::::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
::::::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
:::::::::::::::::::
:::::::::::::::::::Best Regards,
:::::::::::::::::::
:::::::::::::::::::Bill Grimm
:::::::::::::::::Hi Norm,
::::::::::::::::: I agree. That will do it, too.
:::::::::::::::::
:::::::::::::::::All the Best,
:::::::::::::::::
:::::::::::::::::Bill
::::::::::::::Hi Job and Norm,
:::::::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
::::::::::::::
::::::::::::::All the Best,
::::::::::::::
::::::::::::::Bill Grimm
:Job,
:
:Just one more thing: As Norm Leal mentioned in an earlier post, did you visually confirm the filament was lighting in the 7Y4 tube. I worked on Motorola communications equipment back when and the loctal tube sockets were a source of headaches for me by losing contact between the socket and tube pins.
:
:Radiodoc
:**********
:
:
::OK Gentlemen-----I carried out the test to determine if there was DC voltage on anodes of tube 7Y4 as per instructions. Edd, I used one of those little black suckers that you sent and I did receive lots of voltage on the anodes when scraching them. So, do we now assume that tube 7Y4 if ok??? Norm, I guess that the 6X4 tube won’t be any good after all but hopefully the 7Y4 will be ok.
::I notice there are further instructions so I’ll check them out.
::
::
::
::
::::
::::
::::
::::OHH-TAYYY…it looks like we do be OK on that point where the center tap wire connects to the external circuitry and that you are confirming the
::::presence of the combined resistance of #55 and #56 Voltage divider resistor pair.
::::BUT what specific info needed was the resistance read out between the Yellow- Green CT connection and both / either of the Green wires of the HV windings.
::::
::::With what info you supplied at the last…that floating / blinking display is indicative of an open circuit.....instead of the desired ~300 ohms.
::::
::::That then suggests that you might leave the ohmmic metering clip connected between the Yellow- Green CT lead and then take your choice of one of the outer Green HV sec wires to connect other metering wire and then get a hold of the green white wire at the entry point to the T-former and enact a pressing inwards of the wire and then a slight pull on the wire to see if any continuity is intermittently shown on metering. If no results , then the loosening of the 2-4 screws and dropping of the bell covers of the T-former might be in order, to then visually inspect the green white wiring connection and its routing at the sides of the winding..at least we know that the total series connection is made….. but just possibly an open connection having developed at that Green- White CT wire connection.
::::
::::I just might have given you some dupes on the Zeners, from the tolerance respect…I do think that one unit sent was a special precision voltage reference…1N823B with a .005 % reg tolerance… but Zeners are not of the family of diodes which we speak.
::::The units of interest would have been black epoxy molded casings , with 1N4007 marked lengthwise on the side.
::::
::::Addenda: just now caught the :
:::"I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively."...but check for possible intermittency of connectivity. Then with CT connection being solid, I guess the 4007 would be next. ( Or the temporary hay-wiring in of the 5 wires, 7 pin mini socket and in stock 6X4 might be in order)
::::
::::
::::73's de Edd
::::
::::
::::
::::
::::
::::
::::
:::::Ok gentlemen, let's see where we are. First, I measured center tap of HVT winding to chassis (B Minus) and got a reading of 296 ohms. However, after I had completed more testing, etc. I rechecked and couldn't get a reading...out of scale range..STRANGE..
:::::I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
:::::Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
:::::Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
:::::Regards
:::::
:::::
::::::
::::::
::::::
::::::
::::::BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
::::::
::::::Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
::::::
::::::I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
:::::: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
::::::
::::::Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
::::::Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
::::::Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
::::::
::::::I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
::::::
::::::Confirm that I did send you additionals / surplus at that time.
::::::
::::::BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
::::::
::::::BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
::::::
::::::
::::::
::::::73's de Edd
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::::Job,
::::::::
::::::::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
::::::::
::::::::Radiodoc
::::::::**********
:::::::Job,
:::::::
:::::::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
:::::::
:::::::Radiodoc
:::::::**********
:::::::
:::::::
::::::::
::::::::
:::::::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
:::::::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
:::::::::Regards
:::::::::
:::::::::
:::::::::
:::::::::
::::::::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
::::::::::Regards
::::::::::
::::::::::
::::::::::
:::::::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
:::::::::::Bill
:::::::::::
::::::::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
::::::::::::Regards
::::::::::::
::::::::::::
::::::::::::
:::::::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
:::::::::::::
:::::::::::::Bill
:::::::::::::
::::::::::::::Job,
::::::::::::::
::::::::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
::::::::::::::
::::::::::::::Radiodoc
::::::::::::::**********
::::::::::::::
::::::::::::::
::::::::::::::::Hi Job
::::::::::::::::
:::::::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
::::::::::::::::
::::::::::::::::Norm
::::::::::::::::
:::::::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
:::::::::::::::::Regards
:::::::::::::::::
:::::::::::::::::
:::::::::::::::::
:::::::::::::::::::Hi Bill
:::::::::::::::::::
::::::::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:::::::::::::::::::
:::::::::::::::::::Norm
:::::::::::::::::::
::::::::::::::::::::Hi Guys,
:::::::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
:::::::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::::::::::::::::::::
::::::::::::::::::::Best Regards,
::::::::::::::::::::
::::::::::::::::::::Bill Grimm
::::::::::::::::::Hi Norm,
:::::::::::::::::: I agree. That will do it, too.
::::::::::::::::::
::::::::::::::::::All the Best,
::::::::::::::::::
::::::::::::::::::Bill
:::::::::::::::Hi Job and Norm,
::::::::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
:::::::::::::::
:::::::::::::::All the Best,
:::::::::::::::
:::::::::::::::Bill Grimm
:
Hi Job,
Loctal sockets are not nearly as reliable as Octal. Corrosion in the contacts and metal fatigue plague them. 7 and 9 pin miniature sockets have the same problem.
A place where it can show is on the filaments. (Connections to detector diodes are also a problem.) A little resistance in the filament circuit goes a long way in stopping the tube from lighting.
This also explains your frustration, too. This is feindishly subtle.
You may be able to work on pins 1 and 8 to re-establish a good connection. I would replace the tube socket.
Before you do that, though, you may want to use clips leads to connect the 7Y4 or solder in the diodes to see if there is another problem elsewhere in the radio.
Best Regards,
Bill Grimm
If the filament of the 7Y4 is not lighting there will not be any B+. Try measuring the AC filament voltage on the tube pins themselves and not the socket solder tabs. If the voltage is on the socket tabs but not the tube pins, then there is a problem with the tube socket, possibly may need to try to press the socket contacts together. There possibly may be a break between the socket solder tab and the contact the tube pin fits in.
Radiodoc
**********
:Connected ohmmeter probe to wire of center tap and connected other probe of ohmmeter to an outer green wire and with pincers got hold of green/white wire at entry to transformer and tugged and pushed.......no changes visualized or detected on meter. Will dismantle transformer if required. However Doc-----I did not see a glow in tube 7y4. All other tubes had a glow but not this one. Now for a question....How come there is an AC reading of 5.9 volts across pins 1 and 8 and the filament is not glowing???
:
:
:
::Job,
::
::Just one more thing: As Norm Leal mentioned in an earlier post, did you visually confirm the filament was lighting in the 7Y4 tube. I worked on Motorola communications equipment back when and the loctal tube sockets were a source of headaches for me by losing contact between the socket and tube pins.
::
::Radiodoc
::**********
::
::
:::OK Gentlemen-----I carried out the test to determine if there was DC voltage on anodes of tube 7Y4 as per instructions. Edd, I used one of those little black suckers that you sent and I did receive lots of voltage on the anodes when scraching them. So, do we now assume that tube 7Y4 if ok??? Norm, I guess that the 6X4 tube won’t be any good after all but hopefully the 7Y4 will be ok.
:::I notice there are further instructions so I’ll check them out.
:::
:::
:::
:::
:::::
:::::
:::::
:::::OHH-TAYYY…it looks like we do be OK on that point where the center tap wire connects to the external circuitry and that you are confirming the
:::::presence of the combined resistance of #55 and #56 Voltage divider resistor pair.
:::::BUT what specific info needed was the resistance read out between the Yellow- Green CT connection and both / either of the Green wires of the HV windings.
:::::
:::::With what info you supplied at the last…that floating / blinking display is indicative of an open circuit.....instead of the desired ~300 ohms.
:::::
:::::That then suggests that you might leave the ohmmic metering clip connected between the Yellow- Green CT lead and then take your choice of one of the outer Green HV sec wires to connect other metering wire and then get a hold of the green white wire at the entry point to the T-former and enact a pressing inwards of the wire and then a slight pull on the wire to see if any continuity is intermittently shown on metering. If no results , then the loosening of the 2-4 screws and dropping of the bell covers of the T-former might be in order, to then visually inspect the green white wiring connection and its routing at the sides of the winding..at least we know that the total series connection is made….. but just possibly an open connection having developed at that Green- White CT wire connection.
:::::
:::::I just might have given you some dupes on the Zeners, from the tolerance respect…I do think that one unit sent was a special precision voltage reference…1N823B with a .005 % reg tolerance… but Zeners are not of the family of diodes which we speak.
:::::The units of interest would have been black epoxy molded casings , with 1N4007 marked lengthwise on the side.
:::::
:::::Addenda: just now caught the :
::::"I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively."...but check for possible intermittency of connectivity. Then with CT connection being solid, I guess the 4007 would be next. ( Or the temporary hay-wiring in of the 5 wires, 7 pin mini socket and in stock 6X4 might be in order)
:::::
:::::
:::::73's de Edd
:::::
:::::
:::::
:::::
:::::
:::::
:::::
::::::Ok gentlemen, let's see where we are. First, I measured center tap of HVT winding to chassis (B Minus) and got a reading of 296 ohms. However, after I had completed more testing, etc. I rechecked and couldn't get a reading...out of scale range..STRANGE..
::::::I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
::::::Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
::::::Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
::::::Regards
::::::
::::::
:::::::
:::::::
:::::::
:::::::
:::::::BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
:::::::
:::::::Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
:::::::
:::::::I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
::::::: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
:::::::
:::::::Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
:::::::Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
:::::::Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
:::::::
:::::::I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
:::::::
:::::::Confirm that I did send you additionals / surplus at that time.
:::::::
:::::::BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
:::::::
:::::::BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
:::::::
:::::::
:::::::
:::::::73's de Edd
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::::Job,
:::::::::
:::::::::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
:::::::::
:::::::::Radiodoc
:::::::::**********
::::::::Job,
::::::::
::::::::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
::::::::
::::::::Radiodoc
::::::::**********
::::::::
::::::::
:::::::::
:::::::::
::::::::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
::::::::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
::::::::::Regards
::::::::::
::::::::::
::::::::::
::::::::::
:::::::::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
:::::::::::Regards
:::::::::::
:::::::::::
:::::::::::
::::::::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
::::::::::::Bill
::::::::::::
:::::::::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
:::::::::::::Regards
:::::::::::::
:::::::::::::
:::::::::::::
::::::::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
::::::::::::::
::::::::::::::Bill
::::::::::::::
:::::::::::::::Job,
:::::::::::::::
:::::::::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
:::::::::::::::
:::::::::::::::Radiodoc
:::::::::::::::**********
:::::::::::::::
:::::::::::::::
:::::::::::::::::Hi Job
:::::::::::::::::
::::::::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
:::::::::::::::::
:::::::::::::::::Norm
:::::::::::::::::
::::::::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
::::::::::::::::::Regards
::::::::::::::::::
::::::::::::::::::
::::::::::::::::::
::::::::::::::::::::Hi Bill
::::::::::::::::::::
:::::::::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
::::::::::::::::::::
::::::::::::::::::::Norm
::::::::::::::::::::
:::::::::::::::::::::Hi Guys,
::::::::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
::::::::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
:::::::::::::::::::::
:::::::::::::::::::::Best Regards,
:::::::::::::::::::::
:::::::::::::::::::::Bill Grimm
:::::::::::::::::::Hi Norm,
::::::::::::::::::: I agree. That will do it, too.
:::::::::::::::::::
:::::::::::::::::::All the Best,
:::::::::::::::::::
:::::::::::::::::::Bill
::::::::::::::::Hi Job and Norm,
:::::::::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
::::::::::::::::
::::::::::::::::All the Best,
::::::::::::::::
::::::::::::::::Bill Grimm
And the saga continues.......ok, I checked tube 7Y4 to see if there was a glow and there wasn’t. All of the other tubes had a glow coming from them but 7Y4 did not....just checked it again...no glow. Buttttttt I am getting 6.0 AC voltage across the filaments ..1 and 8..measuring on the tube pins and also measuring on the soldering terminals...
It looks like we’re back to square one but I just want to say something and that is, I’m obtaining a wealth of knowledge and information from you kind people on troubleshooting the power supply in a tube radio. No textbook could walk me through the possible problems like you guys have been doing, not only now but also in the past.....OK....enough buttering...lol...I just want to express my appreciation that’s all whether we solve this particular problem or not.
Regards
:Job,
:
:If the filament of the 7Y4 is not lighting there will not be any B+. Try measuring the AC filament voltage on the tube pins themselves and not the socket solder tabs. If the voltage is on the socket tabs but not the tube pins, then there is a problem with the tube socket, possibly may need to try to press the socket contacts together. There possibly may be a break between the socket solder tab and the contact the tube pin fits in.
:
:Radiodoc
:**********
:
:
::Connected ohmmeter probe to wire of center tap and connected other probe of ohmmeter to an outer green wire and with pincers got hold of green/white wire at entry to transformer and tugged and pushed.......no changes visualized or detected on meter. Will dismantle transformer if required. However Doc-----I did not see a glow in tube 7y4. All other tubes had a glow but not this one. Now for a question....How come there is an AC reading of 5.9 volts across pins 1 and 8 and the filament is not glowing???
::
::
::
:::Job,
:::
:::Just one more thing: As Norm Leal mentioned in an earlier post, did you visually confirm the filament was lighting in the 7Y4 tube. I worked on Motorola communications equipment back when and the loctal tube sockets were a source of headaches for me by losing contact between the socket and tube pins.
:::
:::Radiodoc
:::**********
:::
:::
::::OK Gentlemen-----I carried out the test to determine if there was DC voltage on anodes of tube 7Y4 as per instructions. Edd, I used one of those little black suckers that you sent and I did receive lots of voltage on the anodes when scraching them. So, do we now assume that tube 7Y4 if ok??? Norm, I guess that the 6X4 tube won’t be any good after all but hopefully the 7Y4 will be ok.
::::I notice there are further instructions so I’ll check them out.
::::
::::
::::
::::
::::::
::::::
::::::
::::::OHH-TAYYY…it looks like we do be OK on that point where the center tap wire connects to the external circuitry and that you are confirming the
::::::presence of the combined resistance of #55 and #56 Voltage divider resistor pair.
::::::BUT what specific info needed was the resistance read out between the Yellow- Green CT connection and both / either of the Green wires of the HV windings.
::::::
::::::With what info you supplied at the last…that floating / blinking display is indicative of an open circuit.....instead of the desired ~300 ohms.
::::::
::::::That then suggests that you might leave the ohmmic metering clip connected between the Yellow- Green CT lead and then take your choice of one of the outer Green HV sec wires to connect other metering wire and then get a hold of the green white wire at the entry point to the T-former and enact a pressing inwards of the wire and then a slight pull on the wire to see if any continuity is intermittently shown on metering. If no results , then the loosening of the 2-4 screws and dropping of the bell covers of the T-former might be in order, to then visually inspect the green white wiring connection and its routing at the sides of the winding..at least we know that the total series connection is made….. but just possibly an open connection having developed at that Green- White CT wire connection.
::::::
::::::I just might have given you some dupes on the Zeners, from the tolerance respect…I do think that one unit sent was a special precision voltage reference…1N823B with a .005 % reg tolerance… but Zeners are not of the family of diodes which we speak.
::::::The units of interest would have been black epoxy molded casings , with 1N4007 marked lengthwise on the side.
::::::
::::::Addenda: just now caught the :
:::::"I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively."...but check for possible intermittency of connectivity. Then with CT connection being solid, I guess the 4007 would be next. ( Or the temporary hay-wiring in of the 5 wires, 7 pin mini socket and in stock 6X4 might be in order)
::::::
::::::
::::::73's de Edd
::::::
::::::
::::::
::::::
::::::
::::::
::::::
:::::::Ok gentlemen, let's see where we are. First, I measured center tap of HVT winding to chassis (B Minus) and got a reading of 296 ohms. However, after I had completed more testing, etc. I rechecked and couldn't get a reading...out of scale range..STRANGE..
:::::::I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
:::::::Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
:::::::Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
:::::::Regards
:::::::
:::::::
::::::::
::::::::
::::::::
::::::::
::::::::BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
::::::::
::::::::Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
::::::::
::::::::I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
:::::::: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
::::::::
::::::::Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
::::::::Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
::::::::Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
::::::::
::::::::I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
::::::::
::::::::Confirm that I did send you additionals / surplus at that time.
::::::::
::::::::BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
::::::::
::::::::BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
::::::::
::::::::
::::::::
::::::::73's de Edd
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::::Job,
::::::::::
::::::::::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
::::::::::
::::::::::Radiodoc
::::::::::**********
:::::::::Job,
:::::::::
:::::::::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
:::::::::
:::::::::Radiodoc
:::::::::**********
:::::::::
:::::::::
::::::::::
::::::::::
:::::::::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
:::::::::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
:::::::::::Regards
:::::::::::
:::::::::::
:::::::::::
:::::::::::
::::::::::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
::::::::::::Regards
::::::::::::
::::::::::::
::::::::::::
:::::::::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
:::::::::::::Bill
:::::::::::::
::::::::::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
::::::::::::::Regards
::::::::::::::
::::::::::::::
::::::::::::::
:::::::::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
:::::::::::::::
:::::::::::::::Bill
:::::::::::::::
::::::::::::::::Job,
::::::::::::::::
::::::::::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
::::::::::::::::
::::::::::::::::Radiodoc
::::::::::::::::**********
::::::::::::::::
::::::::::::::::
::::::::::::::::::Hi Job
::::::::::::::::::
:::::::::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
::::::::::::::::::
::::::::::::::::::Norm
::::::::::::::::::
:::::::::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
:::::::::::::::::::Regards
:::::::::::::::::::
:::::::::::::::::::
:::::::::::::::::::
:::::::::::::::::::::Hi Bill
:::::::::::::::::::::
::::::::::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:::::::::::::::::::::
:::::::::::::::::::::Norm
:::::::::::::::::::::
::::::::::::::::::::::Hi Guys,
:::::::::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
:::::::::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::::::::::::::::::::::
::::::::::::::::::::::Best Regards,
::::::::::::::::::::::
::::::::::::::::::::::Bill Grimm
::::::::::::::::::::Hi Norm,
:::::::::::::::::::: I agree. That will do it, too.
::::::::::::::::::::
::::::::::::::::::::All the Best,
::::::::::::::::::::
::::::::::::::::::::Bill
:::::::::::::::::Hi Job and Norm,
::::::::::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
:::::::::::::::::
:::::::::::::::::All the Best,
:::::::::::::::::
:::::::::::::::::Bill Grimm
If you have a couple of 1n4007 power supply diodes you can solder them to the socket of the 7Y4 (with the tube removed) to supply B+. The anodes of the diodes go to pin 3 or 6 and both cathodes (bar/stripe end) go to pin 7. Power up the radio and try measuring for B+.
Radiodoc
**********
:
:
:
:
:And the saga continues.......ok, I checked tube 7Y4 to see if there was a glow and there wasn’t. All of the other tubes had a glow coming from them but 7Y4 did not....just checked it again...no glow. Buttttttt I am getting 6.0 AC voltage across the filaments ..1 and 8..measuring on the tube pins and also measuring on the soldering terminals...
:It looks like we’re back to square one but I just want to say something and that is, I’m obtaining a wealth of knowledge and information from you kind people on troubleshooting the power supply in a tube radio. No textbook could walk me through the possible problems like you guys have been doing, not only now but also in the past.....OK....enough buttering...lol...I just want to express my appreciation that’s all whether we solve this particular problem or not.
:Regards
:
:
:
::Job,
::
::If the filament of the 7Y4 is not lighting there will not be any B+. Try measuring the AC filament voltage on the tube pins themselves and not the socket solder tabs. If the voltage is on the socket tabs but not the tube pins, then there is a problem with the tube socket, possibly may need to try to press the socket contacts together. There possibly may be a break between the socket solder tab and the contact the tube pin fits in.
::
::Radiodoc
::**********
::
::
:::Connected ohmmeter probe to wire of center tap and connected other probe of ohmmeter to an outer green wire and with pincers got hold of green/white wire at entry to transformer and tugged and pushed.......no changes visualized or detected on meter. Will dismantle transformer if required. However Doc-----I did not see a glow in tube 7y4. All other tubes had a glow but not this one. Now for a question....How come there is an AC reading of 5.9 volts across pins 1 and 8 and the filament is not glowing???
:::
:::
:::
::::Job,
::::
::::Just one more thing: As Norm Leal mentioned in an earlier post, did you visually confirm the filament was lighting in the 7Y4 tube. I worked on Motorola communications equipment back when and the loctal tube sockets were a source of headaches for me by losing contact between the socket and tube pins.
::::
::::Radiodoc
::::**********
::::
::::
:::::OK Gentlemen-----I carried out the test to determine if there was DC voltage on anodes of tube 7Y4 as per instructions. Edd, I used one of those little black suckers that you sent and I did receive lots of voltage on the anodes when scraching them. So, do we now assume that tube 7Y4 if ok??? Norm, I guess that the 6X4 tube won’t be any good after all but hopefully the 7Y4 will be ok.
:::::I notice there are further instructions so I’ll check them out.
:::::
:::::
:::::
:::::
:::::::
:::::::
:::::::
:::::::OHH-TAYYY…it looks like we do be OK on that point where the center tap wire connects to the external circuitry and that you are confirming the
:::::::presence of the combined resistance of #55 and #56 Voltage divider resistor pair.
:::::::BUT what specific info needed was the resistance read out between the Yellow- Green CT connection and both / either of the Green wires of the HV windings.
:::::::
:::::::With what info you supplied at the last…that floating / blinking display is indicative of an open circuit.....instead of the desired ~300 ohms.
:::::::
:::::::That then suggests that you might leave the ohmmic metering clip connected between the Yellow- Green CT lead and then take your choice of one of the outer Green HV sec wires to connect other metering wire and then get a hold of the green white wire at the entry point to the T-former and enact a pressing inwards of the wire and then a slight pull on the wire to see if any continuity is intermittently shown on metering. If no results , then the loosening of the 2-4 screws and dropping of the bell covers of the T-former might be in order, to then visually inspect the green white wiring connection and its routing at the sides of the winding..at least we know that the total series connection is made….. but just possibly an open connection having developed at that Green- White CT wire connection.
:::::::
:::::::I just might have given you some dupes on the Zeners, from the tolerance respect…I do think that one unit sent was a special precision voltage reference…1N823B with a .005 % reg tolerance… but Zeners are not of the family of diodes which we speak.
:::::::The units of interest would have been black epoxy molded casings , with 1N4007 marked lengthwise on the side.
:::::::
:::::::Addenda: just now caught the :
::::::"I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively."...but check for possible intermittency of connectivity. Then with CT connection being solid, I guess the 4007 would be next. ( Or the temporary hay-wiring in of the 5 wires, 7 pin mini socket and in stock 6X4 might be in order)
:::::::
:::::::
:::::::73's de Edd
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
::::::::Ok gentlemen, let's see where we are. First, I measured center tap of HVT winding to chassis (B Minus) and got a reading of 296 ohms. However, after I had completed more testing, etc. I rechecked and couldn't get a reading...out of scale range..STRANGE..
::::::::I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
::::::::Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
::::::::Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
::::::::Regards
::::::::
::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
:::::::::
:::::::::Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
:::::::::
:::::::::I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
::::::::: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
:::::::::
:::::::::Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
:::::::::Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
:::::::::Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
:::::::::
:::::::::I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
:::::::::
:::::::::Confirm that I did send you additionals / surplus at that time.
:::::::::
:::::::::BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
:::::::::
:::::::::BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
:::::::::
:::::::::
:::::::::
:::::::::73's de Edd
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::::Job,
:::::::::::
:::::::::::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
:::::::::::
:::::::::::Radiodoc
:::::::::::**********
::::::::::Job,
::::::::::
::::::::::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
::::::::::
::::::::::Radiodoc
::::::::::**********
::::::::::
::::::::::
:::::::::::
:::::::::::
::::::::::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
::::::::::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
::::::::::::Regards
::::::::::::
::::::::::::
::::::::::::
::::::::::::
:::::::::::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
:::::::::::::Regards
:::::::::::::
:::::::::::::
:::::::::::::
::::::::::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
::::::::::::::Bill
::::::::::::::
:::::::::::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
:::::::::::::::Regards
:::::::::::::::
:::::::::::::::
:::::::::::::::
::::::::::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
::::::::::::::::
::::::::::::::::Bill
::::::::::::::::
:::::::::::::::::Job,
:::::::::::::::::
:::::::::::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
:::::::::::::::::
:::::::::::::::::Radiodoc
:::::::::::::::::**********
:::::::::::::::::
:::::::::::::::::
:::::::::::::::::::Hi Job
:::::::::::::::::::
::::::::::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
:::::::::::::::::::
:::::::::::::::::::Norm
:::::::::::::::::::
::::::::::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
::::::::::::::::::::Regards
::::::::::::::::::::
::::::::::::::::::::
::::::::::::::::::::
::::::::::::::::::::::Hi Bill
::::::::::::::::::::::
:::::::::::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
::::::::::::::::::::::
::::::::::::::::::::::Norm
::::::::::::::::::::::
:::::::::::::::::::::::Hi Guys,
::::::::::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
::::::::::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
:::::::::::::::::::::::
:::::::::::::::::::::::Best Regards,
:::::::::::::::::::::::
:::::::::::::::::::::::Bill Grimm
:::::::::::::::::::::Hi Norm,
::::::::::::::::::::: I agree. That will do it, too.
:::::::::::::::::::::
:::::::::::::::::::::All the Best,
:::::::::::::::::::::
:::::::::::::::::::::Bill
::::::::::::::::::Hi Job and Norm,
:::::::::::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
::::::::::::::::::
::::::::::::::::::All the Best,
::::::::::::::::::
::::::::::::::::::Bill Grimm
My sincere thanks to you all for sticking with me.
Regards
:Job,
:
:If you have a couple of 1n4007 power supply diodes you can solder them to the socket of the 7Y4 (with the tube removed) to supply B+. The anodes of the diodes go to pin 3 or 6 and both cathodes (bar/stripe end) go to pin 7. Power up the radio and try measuring for B+.
:
:Radiodoc
:**********
:
:
::
::
::
::
::And the saga continues.......ok, I checked tube 7Y4 to see if there was a glow and there wasn’t. All of the other tubes had a glow coming from them but 7Y4 did not....just checked it again...no glow. Buttttttt I am getting 6.0 AC voltage across the filaments ..1 and 8..measuring on the tube pins and also measuring on the soldering terminals...
::It looks like we’re back to square one but I just want to say something and that is, I’m obtaining a wealth of knowledge and information from you kind people on troubleshooting the power supply in a tube radio. No textbook could walk me through the possible problems like you guys have been doing, not only now but also in the past.....OK....enough buttering...lol...I just want to express my appreciation that’s all whether we solve this particular problem or not.
::Regards
::
::
::
:::Job,
:::
:::If the filament of the 7Y4 is not lighting there will not be any B+. Try measuring the AC filament voltage on the tube pins themselves and not the socket solder tabs. If the voltage is on the socket tabs but not the tube pins, then there is a problem with the tube socket, possibly may need to try to press the socket contacts together. There possibly may be a break between the socket solder tab and the contact the tube pin fits in.
:::
:::Radiodoc
:::**********
:::
:::
::::Connected ohmmeter probe to wire of center tap and connected other probe of ohmmeter to an outer green wire and with pincers got hold of green/white wire at entry to transformer and tugged and pushed.......no changes visualized or detected on meter. Will dismantle transformer if required. However Doc-----I did not see a glow in tube 7y4. All other tubes had a glow but not this one. Now for a question....How come there is an AC reading of 5.9 volts across pins 1 and 8 and the filament is not glowing???
::::
::::
::::
:::::Job,
:::::
:::::Just one more thing: As Norm Leal mentioned in an earlier post, did you visually confirm the filament was lighting in the 7Y4 tube. I worked on Motorola communications equipment back when and the loctal tube sockets were a source of headaches for me by losing contact between the socket and tube pins.
:::::
:::::Radiodoc
:::::**********
:::::
:::::
::::::OK Gentlemen-----I carried out the test to determine if there was DC voltage on anodes of tube 7Y4 as per instructions. Edd, I used one of those little black suckers that you sent and I did receive lots of voltage on the anodes when scraching them. So, do we now assume that tube 7Y4 if ok??? Norm, I guess that the 6X4 tube won’t be any good after all but hopefully the 7Y4 will be ok.
::::::I notice there are further instructions so I’ll check them out.
::::::
::::::
::::::
::::::
::::::::
::::::::
::::::::
::::::::OHH-TAYYY…it looks like we do be OK on that point where the center tap wire connects to the external circuitry and that you are confirming the
::::::::presence of the combined resistance of #55 and #56 Voltage divider resistor pair.
::::::::BUT what specific info needed was the resistance read out between the Yellow- Green CT connection and both / either of the Green wires of the HV windings.
::::::::
::::::::With what info you supplied at the last…that floating / blinking display is indicative of an open circuit.....instead of the desired ~300 ohms.
::::::::
::::::::That then suggests that you might leave the ohmmic metering clip connected between the Yellow- Green CT lead and then take your choice of one of the outer Green HV sec wires to connect other metering wire and then get a hold of the green white wire at the entry point to the T-former and enact a pressing inwards of the wire and then a slight pull on the wire to see if any continuity is intermittently shown on metering. If no results , then the loosening of the 2-4 screws and dropping of the bell covers of the T-former might be in order, to then visually inspect the green white wiring connection and its routing at the sides of the winding..at least we know that the total series connection is made….. but just possibly an open connection having developed at that Green- White CT wire connection.
::::::::
::::::::I just might have given you some dupes on the Zeners, from the tolerance respect…I do think that one unit sent was a special precision voltage reference…1N823B with a .005 % reg tolerance… but Zeners are not of the family of diodes which we speak.
::::::::The units of interest would have been black epoxy molded casings , with 1N4007 marked lengthwise on the side.
::::::::
::::::::Addenda: just now caught the :
:::::::"I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively."...but check for possible intermittency of connectivity. Then with CT connection being solid, I guess the 4007 would be next. ( Or the temporary hay-wiring in of the 5 wires, 7 pin mini socket and in stock 6X4 might be in order)
::::::::
::::::::
::::::::73's de Edd
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
:::::::::Ok gentlemen, let's see where we are. First, I measured center tap of HVT winding to chassis (B Minus) and got a reading of 296 ohms. However, after I had completed more testing, etc. I rechecked and couldn't get a reading...out of scale range..STRANGE..
:::::::::I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
:::::::::Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
:::::::::Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
:::::::::Regards
:::::::::
:::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
::::::::::
::::::::::Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
::::::::::
::::::::::I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
:::::::::: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
::::::::::
::::::::::Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
::::::::::Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
::::::::::Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
::::::::::
::::::::::I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
::::::::::
::::::::::Confirm that I did send you additionals / surplus at that time.
::::::::::
::::::::::BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
::::::::::
::::::::::BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
::::::::::
::::::::::
::::::::::
::::::::::73's de Edd
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::::Job,
::::::::::::
::::::::::::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
::::::::::::
::::::::::::Radiodoc
::::::::::::**********
:::::::::::Job,
:::::::::::
:::::::::::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
:::::::::::
:::::::::::Radiodoc
:::::::::::**********
:::::::::::
:::::::::::
::::::::::::
::::::::::::
:::::::::::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
:::::::::::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
:::::::::::::Regards
:::::::::::::
:::::::::::::
:::::::::::::
:::::::::::::
::::::::::::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
::::::::::::::Regards
::::::::::::::
::::::::::::::
::::::::::::::
:::::::::::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
:::::::::::::::Bill
:::::::::::::::
::::::::::::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
::::::::::::::::Regards
::::::::::::::::
::::::::::::::::
::::::::::::::::
:::::::::::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
:::::::::::::::::
:::::::::::::::::Bill
:::::::::::::::::
::::::::::::::::::Job,
::::::::::::::::::
::::::::::::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
::::::::::::::::::
::::::::::::::::::Radiodoc
::::::::::::::::::**********
::::::::::::::::::
::::::::::::::::::
::::::::::::::::::::Hi Job
::::::::::::::::::::
:::::::::::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
::::::::::::::::::::
::::::::::::::::::::Norm
::::::::::::::::::::
:::::::::::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
:::::::::::::::::::::Regards
:::::::::::::::::::::
:::::::::::::::::::::
:::::::::::::::::::::
:::::::::::::::::::::::Hi Bill
:::::::::::::::::::::::
::::::::::::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:::::::::::::::::::::::
:::::::::::::::::::::::Norm
:::::::::::::::::::::::
::::::::::::::::::::::::Hi Guys,
:::::::::::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
:::::::::::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::::::::::::::::::::::::
::::::::::::::::::::::::Best Regards,
::::::::::::::::::::::::
::::::::::::::::::::::::Bill Grimm
::::::::::::::::::::::Hi Norm,
:::::::::::::::::::::: I agree. That will do it, too.
::::::::::::::::::::::
::::::::::::::::::::::All the Best,
::::::::::::::::::::::
::::::::::::::::::::::Bill
:::::::::::::::::::Hi Job and Norm,
::::::::::::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
:::::::::::::::::::
:::::::::::::::::::All the Best,
:::::::::::::::::::
:::::::::::::::::::Bill Grimm
I can't answer your question about why the tube would light in a tube tester and test good and not in the radio socket unless there was/is something defective about the radio tube socket. But by measuring proper filament voltage on the tube pins themselves, the tube should light unless there is a problem with the tube pin connections inside the tube itself. When you acquire a new 7Y4 hopefully there will not be a problem.
Radiodoc
**********
:YES, YES, YES.....Now, how come the tube tester didn't detect this tube being faulty? Was the problem the anodes or cathode being grounded?.....Many questions but I am so excited about getting B plus on this radio and good static coming through when testing. No station yet but that will come....oh yes, I will be ordering those diodes and I'm wondering if there are others I should have in stock also.
:My sincere thanks to you all for sticking with me.
:Regards
:
:
::Job,
::
::If you have a couple of 1n4007 power supply diodes you can solder them to the socket of the 7Y4 (with the tube removed) to supply B+. The anodes of the diodes go to pin 3 or 6 and both cathodes (bar/stripe end) go to pin 7. Power up the radio and try measuring for B+.
::
::Radiodoc
::**********
::
::
:::
:::
:::
:::
:::And the saga continues.......ok, I checked tube 7Y4 to see if there was a glow and there wasn’t. All of the other tubes had a glow coming from them but 7Y4 did not....just checked it again...no glow. Buttttttt I am getting 6.0 AC voltage across the filaments ..1 and 8..measuring on the tube pins and also measuring on the soldering terminals...
:::It looks like we’re back to square one but I just want to say something and that is, I’m obtaining a wealth of knowledge and information from you kind people on troubleshooting the power supply in a tube radio. No textbook could walk me through the possible problems like you guys have been doing, not only now but also in the past.....OK....enough buttering...lol...I just want to express my appreciation that’s all whether we solve this particular problem or not.
:::Regards
:::
:::
:::
::::Job,
::::
::::If the filament of the 7Y4 is not lighting there will not be any B+. Try measuring the AC filament voltage on the tube pins themselves and not the socket solder tabs. If the voltage is on the socket tabs but not the tube pins, then there is a problem with the tube socket, possibly may need to try to press the socket contacts together. There possibly may be a break between the socket solder tab and the contact the tube pin fits in.
::::
::::Radiodoc
::::**********
::::
::::
:::::Connected ohmmeter probe to wire of center tap and connected other probe of ohmmeter to an outer green wire and with pincers got hold of green/white wire at entry to transformer and tugged and pushed.......no changes visualized or detected on meter. Will dismantle transformer if required. However Doc-----I did not see a glow in tube 7y4. All other tubes had a glow but not this one. Now for a question....How come there is an AC reading of 5.9 volts across pins 1 and 8 and the filament is not glowing???
:::::
:::::
:::::
::::::Job,
::::::
::::::Just one more thing: As Norm Leal mentioned in an earlier post, did you visually confirm the filament was lighting in the 7Y4 tube. I worked on Motorola communications equipment back when and the loctal tube sockets were a source of headaches for me by losing contact between the socket and tube pins.
::::::
::::::Radiodoc
::::::**********
::::::
::::::
:::::::OK Gentlemen-----I carried out the test to determine if there was DC voltage on anodes of tube 7Y4 as per instructions. Edd, I used one of those little black suckers that you sent and I did receive lots of voltage on the anodes when scraching them. So, do we now assume that tube 7Y4 if ok??? Norm, I guess that the 6X4 tube won’t be any good after all but hopefully the 7Y4 will be ok.
:::::::I notice there are further instructions so I’ll check them out.
:::::::
:::::::
:::::::
:::::::
:::::::::
:::::::::
:::::::::
:::::::::OHH-TAYYY…it looks like we do be OK on that point where the center tap wire connects to the external circuitry and that you are confirming the
:::::::::presence of the combined resistance of #55 and #56 Voltage divider resistor pair.
:::::::::BUT what specific info needed was the resistance read out between the Yellow- Green CT connection and both / either of the Green wires of the HV windings.
:::::::::
:::::::::With what info you supplied at the last…that floating / blinking display is indicative of an open circuit.....instead of the desired ~300 ohms.
:::::::::
:::::::::That then suggests that you might leave the ohmmic metering clip connected between the Yellow- Green CT lead and then take your choice of one of the outer Green HV sec wires to connect other metering wire and then get a hold of the green white wire at the entry point to the T-former and enact a pressing inwards of the wire and then a slight pull on the wire to see if any continuity is intermittently shown on metering. If no results , then the loosening of the 2-4 screws and dropping of the bell covers of the T-former might be in order, to then visually inspect the green white wiring connection and its routing at the sides of the winding..at least we know that the total series connection is made….. but just possibly an open connection having developed at that Green- White CT wire connection.
:::::::::
:::::::::I just might have given you some dupes on the Zeners, from the tolerance respect…I do think that one unit sent was a special precision voltage reference…1N823B with a .005 % reg tolerance… but Zeners are not of the family of diodes which we speak.
:::::::::The units of interest would have been black epoxy molded casings , with 1N4007 marked lengthwise on the side.
:::::::::
:::::::::Addenda: just now caught the :
::::::::"I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively."...but check for possible intermittency of connectivity. Then with CT connection being solid, I guess the 4007 would be next. ( Or the temporary hay-wiring in of the 5 wires, 7 pin mini socket and in stock 6X4 might be in order)
:::::::::
:::::::::
:::::::::73's de Edd
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
::::::::::Ok gentlemen, let's see where we are. First, I measured center tap of HVT winding to chassis (B Minus) and got a reading of 296 ohms. However, after I had completed more testing, etc. I rechecked and couldn't get a reading...out of scale range..STRANGE..
::::::::::I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
::::::::::Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
::::::::::Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
::::::::::Regards
::::::::::
::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
:::::::::::
:::::::::::Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
:::::::::::
:::::::::::I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
::::::::::: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
:::::::::::
:::::::::::Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
:::::::::::Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
:::::::::::Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
:::::::::::
:::::::::::I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
:::::::::::
:::::::::::Confirm that I did send you additionals / surplus at that time.
:::::::::::
:::::::::::BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
:::::::::::
:::::::::::BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
:::::::::::
:::::::::::
:::::::::::
:::::::::::73's de Edd
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::::Job,
:::::::::::::
:::::::::::::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
:::::::::::::
:::::::::::::Radiodoc
:::::::::::::**********
::::::::::::Job,
::::::::::::
::::::::::::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
::::::::::::
::::::::::::Radiodoc
::::::::::::**********
::::::::::::
::::::::::::
:::::::::::::
:::::::::::::
::::::::::::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
::::::::::::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
::::::::::::::Regards
::::::::::::::
::::::::::::::
::::::::::::::
::::::::::::::
:::::::::::::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
:::::::::::::::Regards
:::::::::::::::
:::::::::::::::
:::::::::::::::
::::::::::::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
::::::::::::::::Bill
::::::::::::::::
:::::::::::::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
:::::::::::::::::Regards
:::::::::::::::::
:::::::::::::::::
:::::::::::::::::
::::::::::::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
::::::::::::::::::
::::::::::::::::::Bill
::::::::::::::::::
:::::::::::::::::::Job,
:::::::::::::::::::
:::::::::::::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
:::::::::::::::::::
:::::::::::::::::::Radiodoc
:::::::::::::::::::**********
:::::::::::::::::::
:::::::::::::::::::
:::::::::::::::::::::Hi Job
:::::::::::::::::::::
::::::::::::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
:::::::::::::::::::::
:::::::::::::::::::::Norm
:::::::::::::::::::::
::::::::::::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
::::::::::::::::::::::Regards
::::::::::::::::::::::
::::::::::::::::::::::
::::::::::::::::::::::
::::::::::::::::::::::::Hi Bill
::::::::::::::::::::::::
:::::::::::::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
::::::::::::::::::::::::
::::::::::::::::::::::::Norm
::::::::::::::::::::::::
:::::::::::::::::::::::::Hi Guys,
::::::::::::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
::::::::::::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
:::::::::::::::::::::::::
:::::::::::::::::::::::::Best Regards,
:::::::::::::::::::::::::
:::::::::::::::::::::::::Bill Grimm
:::::::::::::::::::::::Hi Norm,
::::::::::::::::::::::: I agree. That will do it, too.
:::::::::::::::::::::::
:::::::::::::::::::::::All the Best,
:::::::::::::::::::::::
:::::::::::::::::::::::Bill
::::::::::::::::::::Hi Job and Norm,
:::::::::::::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
::::::::::::::::::::
::::::::::::::::::::All the Best,
::::::::::::::::::::
::::::::::::::::::::Bill Grimm
Well, the sub in of the SS rectifier(s) confirmed the sets circuit components creation of B+ now being a possibility…and best not to run it for any time with those diodes in circuit…..to avoid taxing of the PS components with that much heftier B+ level being created, even the compensatory dropping of the AC input level with a variac, which would also create the somewhat undesired / dampening side effect of the effective filament supply level dropping on all of the tubes.
To be further sure that the EXACT trouble present is pinpointed, you might enact the further tests:
You mentioned not being able to see the filaments of the 7Y4… and I can certainly fathom that …since there are soooo many of those locktals type tubes that are so silvered up internally …that viewing is dang nigh impossible…cept’n thru a few unsilvered nooks and crannies down at the bottoms, unless the bottom shell is also covering that area up!
Buttttttt I am getting 6.0 AC voltage across the filaments ..1 and 8..measuring on the tube pins and also measuring on the soldering terminals...
With the tube testing good in a tester and wiring ans accompanying voltages good right up to the tube lugs...looks like the mentioned tube socket needs investigating.
Since there is confirmation of filament supply getting right up to the tube socket pins…plus no apparent loose connections at the power transformer , or enroute, if its wires passed the aforementioned pushing -pulling testing.
What I might suggest is pulling out the 7Y4 tube and taking in hand and enact an ohmmic check between its two filament pins and take note of its ~ resistive value.
Then plug the tube into its socket and go to its filament supply wires that come from the power t-former and clip / unsolder one, or both of the filament supply wires so that one tube socket pin connection is completely out of circuit and its reading will not reflect either the shunting otherwise presented by the filament winding of the PT-former or the sets pilot lamps. Expect the reading taken at the sockets filament pins to dupe the ohmmic value previously read.
Preferably, make the ohmmeter connection with some clip leads, so that with free hands, the tube can be tilted/twisted/ turned to see if any dropping / intermittentcy of that continuity shows up. If that shows up suspect the quite rare breaking of a pin internally, or the more common, corrosion or spreading apart of the pin contacting surfaces of a socket tube pin connection where it is supposed to grip the tubes pin.
73's de Edd
:YES, YES, YES.....Now, how come the tube tester didn't detect this tube being faulty? Was the problem the anodes or cathode being grounded?.....Many questions but I am so excited about getting B plus on this radio and good static coming through when testing. No station yet but that will come....oh yes, I will be ordering those diodes and I'm wondering if there are others I should have in stock also.
:My sincere thanks to you all for sticking with me.
:Regards
:
:
::Job,
::
::If you have a couple of 1n4007 power supply diodes you can solder them to the socket of the 7Y4 (with the tube removed) to supply B+. The anodes of the diodes go to pin 3 or 6 and both cathodes (bar/stripe end) go to pin 7. Power up the radio and try measuring for B+.
::
::Radiodoc
::**********
::
::
:::
:::
:::
:::
:::And the saga continues.......ok, I checked tube 7Y4 to see if there was a glow and there wasn’t. All of the other tubes had a glow coming from them but 7Y4 did not....just checked it again...no glow. Buttttttt I am getting 6.0 AC voltage across the filaments ..1 and 8..measuring on the tube pins and also measuring on the soldering terminals...
:::It looks like we’re back to square one but I just want to say something and that is, I’m obtaining a wealth of knowledge and information from you kind people on troubleshooting the power supply in a tube radio. No textbook could walk me through the possible problems like you guys have been doing, not only now but also in the past.....OK....enough buttering...lol...I just want to express my appreciation that’s all whether we solve this particular problem or not.
:::Regards
:::
:::
:::
::::Job,
::::
::::If the filament of the 7Y4 is not lighting there will not be any B+. Try measuring the AC filament voltage on the tube pins themselves and not the socket solder tabs. If the voltage is on the socket tabs but not the tube pins, then there is a problem with the tube socket, possibly may need to try to press the socket contacts together. There possibly may be a break between the socket solder tab and the contact the tube pin fits in.
::::
::::Radiodoc
::::**********
::::
::::
:::::Connected ohmmeter probe to wire of center tap and connected other probe of ohmmeter to an outer green wire and with pincers got hold of green/white wire at entry to transformer and tugged and pushed.......no changes visualized or detected on meter. Will dismantle transformer if required. However Doc-----I did not see a glow in tube 7y4. All other tubes had a glow but not this one. Now for a question....How come there is an AC reading of 5.9 volts across pins 1 and 8 and the filament is not glowing???
:::::
:::::
:::::
::::::Job,
::::::
::::::Just one more thing: As Norm Leal mentioned in an earlier post, did you visually confirm the filament was lighting in the 7Y4 tube. I worked on Motorola communications equipment back when and the loctal tube sockets were a source of headaches for me by losing contact between the socket and tube pins.
::::::
::::::Radiodoc
::::::**********
::::::
::::::
:::::::OK Gentlemen-----I carried out the test to determine if there was DC voltage on anodes of tube 7Y4 as per instructions. Edd, I used one of those little black suckers that you sent and I did receive lots of voltage on the anodes when scraching them. So, do we now assume that tube 7Y4 if ok??? Norm, I guess that the 6X4 tube won’t be any good after all but hopefully the 7Y4 will be ok.
:::::::I notice there are further instructions so I’ll check them out.
:::::::
:::::::
:::::::
:::::::
:::::::::
:::::::::
:::::::::
:::::::::OHH-TAYYY…it looks like we do be OK on that point where the center tap wire connects to the external circuitry and that you are confirming the
:::::::::presence of the combined resistance of #55 and #56 Voltage divider resistor pair.
:::::::::BUT what specific info needed was the resistance read out between the Yellow- Green CT connection and both / either of the Green wires of the HV windings.
:::::::::
:::::::::With what info you supplied at the last…that floating / blinking display is indicative of an open circuit.....instead of the desired ~300 ohms.
:::::::::
:::::::::That then suggests that you might leave the ohmmic metering clip connected between the Yellow- Green CT lead and then take your choice of one of the outer Green HV sec wires to connect other metering wire and then get a hold of the green white wire at the entry point to the T-former and enact a pressing inwards of the wire and then a slight pull on the wire to see if any continuity is intermittently shown on metering. If no results , then the loosening of the 2-4 screws and dropping of the bell covers of the T-former might be in order, to then visually inspect the green white wiring connection and its routing at the sides of the winding..at least we know that the total series connection is made….. but just possibly an open connection having developed at that Green- White CT wire connection.
:::::::::
:::::::::I just might have given you some dupes on the Zeners, from the tolerance respect…I do think that one unit sent was a special precision voltage reference…1N823B with a .005 % reg tolerance… but Zeners are not of the family of diodes which we speak.
:::::::::The units of interest would have been black epoxy molded casings , with 1N4007 marked lengthwise on the side.
:::::::::
:::::::::Addenda: just now caught the :
::::::::"I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively."...but check for possible intermittency of connectivity. Then with CT connection being solid, I guess the 4007 would be next. ( Or the temporary hay-wiring in of the 5 wires, 7 pin mini socket and in stock 6X4 might be in order)
:::::::::
:::::::::
:::::::::73's de Edd
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
::::::::::Ok gentlemen, let's see where we are. First, I measured center tap of HVT winding to chassis (B Minus) and got a reading of 296 ohms. However, after I had completed more testing, etc. I rechecked and couldn't get a reading...out of scale range..STRANGE..
::::::::::I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
::::::::::Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
::::::::::Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
::::::::::Regards
::::::::::
::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
:::::::::::
:::::::::::Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
:::::::::::
:::::::::::I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
::::::::::: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
:::::::::::
:::::::::::Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
:::::::::::Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
:::::::::::Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
:::::::::::
:::::::::::I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
:::::::::::
:::::::::::Confirm that I did send you additionals / surplus at that time.
:::::::::::
:::::::::::BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
:::::::::::
:::::::::::BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
:::::::::::
:::::::::::
:::::::::::
:::::::::::73's de Edd
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::::Job,
:::::::::::::
:::::::::::::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
:::::::::::::
:::::::::::::Radiodoc
:::::::::::::**********
::::::::::::Job,
::::::::::::
::::::::::::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
::::::::::::
::::::::::::Radiodoc
::::::::::::**********
::::::::::::
::::::::::::
:::::::::::::
:::::::::::::
::::::::::::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
::::::::::::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
::::::::::::::Regards
::::::::::::::
::::::::::::::
::::::::::::::
::::::::::::::
:::::::::::::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
:::::::::::::::Regards
:::::::::::::::
:::::::::::::::
:::::::::::::::
::::::::::::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
::::::::::::::::Bill
::::::::::::::::
:::::::::::::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
:::::::::::::::::Regards
:::::::::::::::::
:::::::::::::::::
:::::::::::::::::
::::::::::::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
::::::::::::::::::
::::::::::::::::::Bill
::::::::::::::::::
:::::::::::::::::::Job,
:::::::::::::::::::
:::::::::::::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
:::::::::::::::::::
:::::::::::::::::::Radiodoc
:::::::::::::::::::**********
:::::::::::::::::::
:::::::::::::::::::
:::::::::::::::::::::Hi Job
:::::::::::::::::::::
::::::::::::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
:::::::::::::::::::::
:::::::::::::::::::::Norm
:::::::::::::::::::::
::::::::::::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
::::::::::::::::::::::Regards
::::::::::::::::::::::
::::::::::::::::::::::
::::::::::::::::::::::
::::::::::::::::::::::::Hi Bill
::::::::::::::::::::::::
:::::::::::::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
::::::::::::::::::::::::
::::::::::::::::::::::::Norm
::::::::::::::::::::::::
:::::::::::::::::::::::::Hi Guys,
::::::::::::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
::::::::::::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
:::::::::::::::::::::::::
:::::::::::::::::::::::::Best Regards,
:::::::::::::::::::::::::
:::::::::::::::::::::::::Bill Grimm
:::::::::::::::::::::::Hi Norm,
::::::::::::::::::::::: I agree. That will do it, too.
:::::::::::::::::::::::
:::::::::::::::::::::::All the Best,
:::::::::::::::::::::::
:::::::::::::::::::::::Bill
::::::::::::::::::::Hi Job and Norm,
:::::::::::::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
::::::::::::::::::::
::::::::::::::::::::All the Best,
::::::::::::::::::::
::::::::::::::::::::Bill Grimm
I did go and retrieve him from the wastebasket for this testing but now I don’t even get any continuity at all from pin 1 and pin 8, so there goes our test Edd. Anyhow, I did proceed with the socket testing as per instructions and got a reading of 0.3 ohms across pins 1 and 8.
When I get my order of tubes in I’ll let you all know how things work out. In the mean time I did power up using the 1N4007 diodes for a couple of minutes and received loud and clear audio from stations...great sounding radio.
Thanks everyone
:
:
:
:
:
:Well, the sub in of the SS rectifier(s) confirmed the sets circuit components creation of B+ now being a possibility…and best not to run it for any time with those diodes in circuit…..to avoid taxing of the PS components with that much heftier B+ level being created, even the compensatory dropping of the AC input level with a variac, which would also create the somewhat undesired / dampening side effect of the effective filament supply level dropping on all of the tubes.
:
:
:To be further sure that the EXACT trouble present is pinpointed, you might enact the further tests:
:
:You mentioned not being able to see the filaments of the 7Y4… and I can certainly fathom that …since there are soooo many of those locktals type tubes that are so silvered up internally …that viewing is dang nigh impossible…cept’n thru a few unsilvered nooks and crannies down at the bottoms, unless the bottom shell is also covering that area up!
:
:
:
:
:Buttttttt I am getting 6.0 AC voltage across the filaments ..1 and 8..measuring on the tube pins and also measuring on the soldering terminals...
:
:
:With the tube testing good in a tester and wiring ans accompanying voltages good right up to the tube lugs...looks like the mentioned tube socket needs investigating.
:Since there is confirmation of filament supply getting right up to the tube socket pins…plus no apparent loose connections at the power transformer , or enroute, if its wires passed the aforementioned pushing -pulling testing.
:
:What I might suggest is pulling out the 7Y4 tube and taking in hand and enact an ohmmic check between its two filament pins and take note of its ~ resistive value.
:Then plug the tube into its socket and go to its filament supply wires that come from the power t-former and clip / unsolder one, or both of the filament supply wires so that one tube socket pin connection is completely out of circuit and its reading will not reflect either the shunting otherwise presented by the filament winding of the PT-former or the sets pilot lamps. Expect the reading taken at the sockets filament pins to dupe the ohmmic value previously read.
:Preferably, make the ohmmeter connection with some clip leads, so that with free hands, the tube can be tilted/twisted/ turned to see if any dropping / intermittentcy of that continuity shows up. If that shows up suspect the quite rare breaking of a pin internally, or the more common, corrosion or spreading apart of the pin contacting surfaces of a socket tube pin connection where it is supposed to grip the tubes pin.
:
:
:73's de Edd
:
:
:
:
:
:
:
:
::YES, YES, YES.....Now, how come the tube tester didn't detect this tube being faulty? Was the problem the anodes or cathode being grounded?.....Many questions but I am so excited about getting B plus on this radio and good static coming through when testing. No station yet but that will come....oh yes, I will be ordering those diodes and I'm wondering if there are others I should have in stock also.
::My sincere thanks to you all for sticking with me.
::Regards
::
::
:::Job,
:::
:::If you have a couple of 1n4007 power supply diodes you can solder them to the socket of the 7Y4 (with the tube removed) to supply B+. The anodes of the diodes go to pin 3 or 6 and both cathodes (bar/stripe end) go to pin 7. Power up the radio and try measuring for B+.
:::
:::Radiodoc
:::**********
:::
:::
::::
::::
::::
::::
::::And the saga continues.......ok, I checked tube 7Y4 to see if there was a glow and there wasn’t. All of the other tubes had a glow coming from them but 7Y4 did not....just checked it again...no glow. Buttttttt I am getting 6.0 AC voltage across the filaments ..1 and 8..measuring on the tube pins and also measuring on the soldering terminals...
::::It looks like we’re back to square one but I just want to say something and that is, I’m obtaining a wealth of knowledge and information from you kind people on troubleshooting the power supply in a tube radio. No textbook could walk me through the possible problems like you guys have been doing, not only now but also in the past.....OK....enough buttering...lol...I just want to express my appreciation that’s all whether we solve this particular problem or not.
::::Regards
::::
::::
::::
:::::Job,
:::::
:::::If the filament of the 7Y4 is not lighting there will not be any B+. Try measuring the AC filament voltage on the tube pins themselves and not the socket solder tabs. If the voltage is on the socket tabs but not the tube pins, then there is a problem with the tube socket, possibly may need to try to press the socket contacts together. There possibly may be a break between the socket solder tab and the contact the tube pin fits in.
:::::
:::::Radiodoc
:::::**********
:::::
:::::
::::::Connected ohmmeter probe to wire of center tap and connected other probe of ohmmeter to an outer green wire and with pincers got hold of green/white wire at entry to transformer and tugged and pushed.......no changes visualized or detected on meter. Will dismantle transformer if required. However Doc-----I did not see a glow in tube 7y4. All other tubes had a glow but not this one. Now for a question....How come there is an AC reading of 5.9 volts across pins 1 and 8 and the filament is not glowing???
::::::
::::::
::::::
:::::::Job,
:::::::
:::::::Just one more thing: As Norm Leal mentioned in an earlier post, did you visually confirm the filament was lighting in the 7Y4 tube. I worked on Motorola communications equipment back when and the loctal tube sockets were a source of headaches for me by losing contact between the socket and tube pins.
:::::::
:::::::Radiodoc
:::::::**********
:::::::
:::::::
::::::::OK Gentlemen-----I carried out the test to determine if there was DC voltage on anodes of tube 7Y4 as per instructions. Edd, I used one of those little black suckers that you sent and I did receive lots of voltage on the anodes when scraching them. So, do we now assume that tube 7Y4 if ok??? Norm, I guess that the 6X4 tube won’t be any good after all but hopefully the 7Y4 will be ok.
::::::::I notice there are further instructions so I’ll check them out.
::::::::
::::::::
::::::::
::::::::
::::::::::
::::::::::
::::::::::
::::::::::OHH-TAYYY…it looks like we do be OK on that point where the center tap wire connects to the external circuitry and that you are confirming the
::::::::::presence of the combined resistance of #55 and #56 Voltage divider resistor pair.
::::::::::BUT what specific info needed was the resistance read out between the Yellow- Green CT connection and both / either of the Green wires of the HV windings.
::::::::::
::::::::::With what info you supplied at the last…that floating / blinking display is indicative of an open circuit.....instead of the desired ~300 ohms.
::::::::::
::::::::::That then suggests that you might leave the ohmmic metering clip connected between the Yellow- Green CT lead and then take your choice of one of the outer Green HV sec wires to connect other metering wire and then get a hold of the green white wire at the entry point to the T-former and enact a pressing inwards of the wire and then a slight pull on the wire to see if any continuity is intermittently shown on metering. If no results , then the loosening of the 2-4 screws and dropping of the bell covers of the T-former might be in order, to then visually inspect the green white wiring connection and its routing at the sides of the winding..at least we know that the total series connection is made….. but just possibly an open connection having developed at that Green- White CT wire connection.
::::::::::
::::::::::I just might have given you some dupes on the Zeners, from the tolerance respect…I do think that one unit sent was a special precision voltage reference…1N823B with a .005 % reg tolerance… but Zeners are not of the family of diodes which we speak.
::::::::::The units of interest would have been black epoxy molded casings , with 1N4007 marked lengthwise on the side.
::::::::::
::::::::::Addenda: just now caught the :
:::::::::"I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively."...but check for possible intermittency of connectivity. Then with CT connection being solid, I guess the 4007 would be next. ( Or the temporary hay-wiring in of the 5 wires, 7 pin mini socket and in stock 6X4 might be in order)
::::::::::
::::::::::
::::::::::73's de Edd
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
:::::::::::Ok gentlemen, let's see where we are. First, I measured center tap of HVT winding to chassis (B Minus) and got a reading of 296 ohms. However, after I had completed more testing, etc. I rechecked and couldn't get a reading...out of scale range..STRANGE..
:::::::::::I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
:::::::::::Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
:::::::::::Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
:::::::::::Regards
:::::::::::
:::::::::::
::::::::::::
::::::::::::
::::::::::::
::::::::::::
::::::::::::BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
::::::::::::
::::::::::::Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
::::::::::::
::::::::::::I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
:::::::::::: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
::::::::::::
::::::::::::Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
::::::::::::Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
::::::::::::Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
::::::::::::
::::::::::::I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
::::::::::::
::::::::::::Confirm that I did send you additionals / surplus at that time.
::::::::::::
::::::::::::BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
::::::::::::
::::::::::::BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
::::::::::::
::::::::::::
::::::::::::
::::::::::::73's de Edd
::::::::::::
::::::::::::
::::::::::::
::::::::::::
::::::::::::
::::::::::::
::::::::::::
::::::::::::
::::::::::::::Job,
::::::::::::::
::::::::::::::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
::::::::::::::
::::::::::::::Radiodoc
::::::::::::::**********
:::::::::::::Job,
:::::::::::::
:::::::::::::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
:::::::::::::
:::::::::::::Radiodoc
:::::::::::::**********
:::::::::::::
:::::::::::::
::::::::::::::
::::::::::::::
:::::::::::::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
:::::::::::::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
:::::::::::::::Regards
:::::::::::::::
:::::::::::::::
:::::::::::::::
:::::::::::::::
::::::::::::::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
::::::::::::::::Regards
::::::::::::::::
::::::::::::::::
::::::::::::::::
:::::::::::::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
:::::::::::::::::Bill
:::::::::::::::::
::::::::::::::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
::::::::::::::::::Regards
::::::::::::::::::
::::::::::::::::::
::::::::::::::::::
:::::::::::::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
:::::::::::::::::::
:::::::::::::::::::Bill
:::::::::::::::::::
::::::::::::::::::::Job,
::::::::::::::::::::
::::::::::::::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
::::::::::::::::::::
::::::::::::::::::::Radiodoc
::::::::::::::::::::**********
::::::::::::::::::::
::::::::::::::::::::
::::::::::::::::::::::Hi Job
::::::::::::::::::::::
:::::::::::::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
::::::::::::::::::::::
::::::::::::::::::::::Norm
::::::::::::::::::::::
:::::::::::::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
:::::::::::::::::::::::Regards
:::::::::::::::::::::::
:::::::::::::::::::::::
:::::::::::::::::::::::
:::::::::::::::::::::::::Hi Bill
:::::::::::::::::::::::::
::::::::::::::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
:::::::::::::::::::::::::
:::::::::::::::::::::::::Norm
:::::::::::::::::::::::::
::::::::::::::::::::::::::Hi Guys,
:::::::::::::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
:::::::::::::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
::::::::::::::::::::::::::
::::::::::::::::::::::::::Best Regards,
::::::::::::::::::::::::::
::::::::::::::::::::::::::Bill Grimm
::::::::::::::::::::::::Hi Norm,
:::::::::::::::::::::::: I agree. That will do it, too.
::::::::::::::::::::::::
::::::::::::::::::::::::All the Best,
::::::::::::::::::::::::
::::::::::::::::::::::::Bill
:::::::::::::::::::::Hi Job and Norm,
::::::::::::::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
:::::::::::::::::::::
:::::::::::::::::::::All the Best,
:::::::::::::::::::::
:::::::::::::::::::::Bill Grimm
Oh the misfortunes of man, or a tube in this case. This is sort of funny but it probably causes us to guess as to the outcome of this “case”. Last night when removing this 7y4 tube from its socket I inadvertently crushed the glass casing.....naturally I felt sorry for the little guy but he was holding real tight and I had to wiggle and twist and then...crushhhhh....
WOW …I would consider yourself lucky that you didn’t end up with any errant shards of glass penetrating into your fingers. Unless gloved, but I never have used them thru the years, except for large power tubes that were still hot and I was real antsy on getting a new one changed into the socket.
I did go and retrieve him from the wastebasket for this testing but now I don’t even get any continuity at all from pin 1 and pin 8, so there goes our test Edd.
I would have expected that filament to have survived intact, since it was cold anyhow, just prior to the unplugging action.
Anyhow, I did proceed with the socket testing as per instructions and got a reading of 0.3 ohms across pins 1 and 8.
That would not have been a valid test manner of the tube and its connectivity thru both of its filament terminals. In your test mode, you are just reading the filament winding of the PT-former and the shunting pilot lamps…… the prior, specified test condition was to have that end disconnected…. out of circuit… and then be making a test from the tube socket terminal down thru the clamping/pinching action of that pin onto its tube filament pin and then thru the filament resistance and over to the clamping/pinching action of the other filament up thru its exit as the other tube socket wiring terminal.
When I get my order of tubes in I’ll let you all know how things work out. In the mean time I did power up using the 1N4007 diodes for a couple of minutes and received loud and clear audio from stations...great sounding radio.
Thanks everyone
73's de Edd
::
::
::
::Well, the sub in of the SS rectifier(s) confirmed the sets circuit components creation of B+ now being a possibility…and best not to run it for any time with those diodes in circuit…..to avoid taxing of the PS components with that much heftier B+ level being created, even the compensatory dropping of the AC input level with a variac, which would also create the somewhat undesired / dampening side effect of the effective filament supply level dropping on all of the tubes.
::
::
::To be further sure that the EXACT trouble present is pinpointed, you might enact the further tests:
::
::You mentioned not being able to see the filaments of the 7Y4… and I can certainly fathom that …since there are soooo many of those locktals type tubes that are so silvered up internally …that viewing is dang nigh impossible…cept’n thru a few unsilvered nooks and crannies down at the bottoms, unless the bottom shell is also covering that area up!
::
::
::
::
::Buttttttt I am getting 6.0 AC voltage across the filaments ..1 and 8..measuring on the tube pins and also measuring on the soldering terminals...
::
::
::With the tube testing good in a tester and wiring ans accompanying voltages good right up to the tube lugs...looks like the mentioned tube socket needs investigating.
::Since there is confirmation of filament supply getting right up to the tube socket pins…plus no apparent loose connections at the power transformer , or enroute, if its wires passed the aforementioned pushing -pulling testing.
::
::What I might suggest is pulling out the 7Y4 tube and taking in hand and enact an ohmmic check between its two filament pins and take note of its ~ resistive value.
::Then plug the tube into its socket and go to its filament supply wires that come from the power t-former and clip / unsolder one, or both of the filament supply wires so that one tube socket pin connection is completely out of circuit and its reading will not reflect either the shunting otherwise presented by the filament winding of the PT-former or the sets pilot lamps. Expect the reading taken at the sockets filament pins to dupe the ohmmic value previously read.
::Preferably, make the ohmmeter connection with some clip leads, so that with free hands, the tube can be tilted/twisted/ turned to see if any dropping / intermittentcy of that continuity shows up. If that shows up suspect the quite rare breaking of a pin internally, or the more common, corrosion or spreading apart of the pin contacting surfaces of a socket tube pin connection where it is supposed to grip the tubes pin.
::
::
::73's de Edd
::
::
::
::
::
::
::
::
:::YES, YES, YES.....Now, how come the tube tester didn't detect this tube being faulty? Was the problem the anodes or cathode being grounded?.....Many questions but I am so excited about getting B plus on this radio and good static coming through when testing. No station yet but that will come....oh yes, I will be ordering those diodes and I'm wondering if there are others I should have in stock also.
:::My sincere thanks to you all for sticking with me.
:::Regards
:::
:::
::::Job,
::::
::::If you have a couple of 1n4007 power supply diodes you can solder them to the socket of the 7Y4 (with the tube removed) to supply B+. The anodes of the diodes go to pin 3 or 6 and both cathodes (bar/stripe end) go to pin 7. Power up the radio and try measuring for B+.
::::
::::Radiodoc
::::**********
::::
::::
:::::
:::::
:::::
:::::
:::::And the saga continues.......ok, I checked tube 7Y4 to see if there was a glow and there wasn’t. All of the other tubes had a glow coming from them but 7Y4 did not....just checked it again...no glow. Buttttttt I am getting 6.0 AC voltage across the filaments ..1 and 8..measuring on the tube pins and also measuring on the soldering terminals...
:::::It looks like we’re back to square one but I just want to say something and that is, I’m obtaining a wealth of knowledge and information from you kind people on troubleshooting the power supply in a tube radio. No textbook could walk me through the possible problems like you guys have been doing, not only now but also in the past.....OK....enough buttering...lol...I just want to express my appreciation that’s all whether we solve this particular problem or not.
:::::Regards
:::::
:::::
:::::
::::::Job,
::::::
::::::If the filament of the 7Y4 is not lighting there will not be any B+. Try measuring the AC filament voltage on the tube pins themselves and not the socket solder tabs. If the voltage is on the socket tabs but not the tube pins, then there is a problem with the tube socket, possibly may need to try to press the socket contacts together. There possibly may be a break between the socket solder tab and the contact the tube pin fits in.
::::::
::::::Radiodoc
::::::**********
::::::
::::::
:::::::Connected ohmmeter probe to wire of center tap and connected other probe of ohmmeter to an outer green wire and with pincers got hold of green/white wire at entry to transformer and tugged and pushed.......no changes visualized or detected on meter. Will dismantle transformer if required. However Doc-----I did not see a glow in tube 7y4. All other tubes had a glow but not this one. Now for a question....How come there is an AC reading of 5.9 volts across pins 1 and 8 and the filament is not glowing???
:::::::
:::::::
:::::::
::::::::Job,
::::::::
::::::::Just one more thing: As Norm Leal mentioned in an earlier post, did you visually confirm the filament was lighting in the 7Y4 tube. I worked on Motorola communications equipment back when and the loctal tube sockets were a source of headaches for me by losing contact between the socket and tube pins.
::::::::
::::::::Radiodoc
::::::::**********
::::::::
::::::::
:::::::::OK Gentlemen-----I carried out the test to determine if there was DC voltage on anodes of tube 7Y4 as per instructions. Edd, I used one of those little black suckers that you sent and I did receive lots of voltage on the anodes when scraching them. So, do we now assume that tube 7Y4 if ok??? Norm, I guess that the 6X4 tube won’t be any good after all but hopefully the 7Y4 will be ok.
:::::::::I notice there are further instructions so I’ll check them out.
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::OHH-TAYYY…it looks like we do be OK on that point where the center tap wire connects to the external circuitry and that you are confirming the
:::::::::::presence of the combined resistance of #55 and #56 Voltage divider resistor pair.
:::::::::::BUT what specific info needed was the resistance read out between the Yellow- Green CT connection and both / either of the Green wires of the HV windings.
:::::::::::
:::::::::::With what info you supplied at the last…that floating / blinking display is indicative of an open circuit.....instead of the desired ~300 ohms.
:::::::::::
:::::::::::That then suggests that you might leave the ohmmic metering clip connected between the Yellow- Green CT lead and then take your choice of one of the outer Green HV sec wires to connect other metering wire and then get a hold of the green white wire at the entry point to the T-former and enact a pressing inwards of the wire and then a slight pull on the wire to see if any continuity is intermittently shown on metering. If no results , then the loosening of the 2-4 screws and dropping of the bell covers of the T-former might be in order, to then visually inspect the green white wiring connection and its routing at the sides of the winding..at least we know that the total series connection is made….. but just possibly an open connection having developed at that Green- White CT wire connection.
:::::::::::
:::::::::::I just might have given you some dupes on the Zeners, from the tolerance respect…I do think that one unit sent was a special precision voltage reference…1N823B with a .005 % reg tolerance… but Zeners are not of the family of diodes which we speak.
:::::::::::The units of interest would have been black epoxy molded casings , with 1N4007 marked lengthwise on the side.
:::::::::::
:::::::::::Addenda: just now caught the :
::::::::::"I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively."...but check for possible intermittency of connectivity. Then with CT connection being solid, I guess the 4007 would be next. ( Or the temporary hay-wiring in of the 5 wires, 7 pin mini socket and in stock 6X4 might be in order)
:::::::::::
:::::::::::
:::::::::::73's de Edd
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
::::::::::::Ok gentlemen, let's see where we are. First, I measured center tap of HVT winding to chassis (B Minus) and got a reading of 296 ohms. However, after I had completed more testing, etc. I rechecked and couldn't get a reading...out of scale range..STRANGE..
::::::::::::I also checked center tap of HVT to pin 3 and pin 6 of tube 7Y4 and got readings of 276 ohms and 277 ohms respectively.
::::::::::::Question... can tube 6x4 substitute for 7Y4 if I do the necessary wiring changes....not much, just three wires I believe?
::::::::::::Edd, I do believe you sent me extra zener diodes so I'll see if I can find them and do the test suggested. Thanks for all the suggestions guys and I'll get back to you later.
::::::::::::Regards
::::::::::::
::::::::::::
:::::::::::::
:::::::::::::
:::::::::::::
:::::::::::::
:::::::::::::BOYYYYY….’ dis do be one looong convoluted thread, very hard to extract and pull out the relevant data. Thought that all would be solved now, what with all of the the good info already being given.
:::::::::::::
:::::::::::::Just as I am ready to post this I see that Le Radiodoctuer has just posted and also hit upon the irrelevance of the situation of the nodes and loads, AF out t-former, field coil, etc on the B+ circuitry on downstream from the 7Y4. ...IF there is no initial B+ right at the 7Y4 circuitry proper
:::::::::::::
:::::::::::::I see that you made no reference as to the resistance reading….. when you take a power down resistance ohmmage of the resistance of pin 3 to the green yellow…the schema shows….center tap wire from the HV sec winding of the transformer, and then from pin 6 to that same center tap wire. Thus establishing that that connection is not open inside the transformer, or between that point and over to the normal connection juncture that the center tap wire goes on over to, should your meter wire have been placed over at that point.
::::::::::::: At any rate you are then confirming the integrity of the ~300-300 ohm readings of the two parts of the secondary of the HV winding to its center tap AND its connection being made and extended on OUTSIDE of the transformer proper with its wire.
:::::::::::::
:::::::::::::Your tube tester supposedly confirmed emission of the rect tube, but with a filament /cathode combo, that could be in error unless a dynamic load was imposed upon it within the tester circuitry. I was in concurrence with the suggested SS rect sub as suggested, but this info was not poked up until just now. My thought was the given assumption of the #57 electrolytic being good and the affixing of your metering medium, set in its DC mode , with the negative lead going to the HV center tap wire of the power t-former and then have positive lead clipped to the pin 7 (cathode) of the rect tube.
:::::::::::::Then you clip a test lead connector to the cathode of the rect tube and the other ends connector of the text lead receives the anode of a 1N4007
:::::::::::::Diode lead wire within its clip. Then you power up the set and observe the DC metering and hold the wire by its insulated portion and just scratch …like a match…either pin 3 or 6 of the rectifier tube and see if the elusive B+ then makes its appearance. If so, wait just a second until you can see its bleed down just a bit and then do the quick scratch on the other plate connection to confirm that it also comes up. If you then have B+ created from both halves of the power transformer winding, looks like a good 7Y4 is in order.
:::::::::::::
:::::::::::::I know that sometime back when you had problems with a “battery eliminator” power supply, that I sent you adequate Zener diodes for doing its repair and had ALSO sent you a supply of 1N4007’s to additionally use in arranging them as steering / isolation diodes for an even more thorough protection of that repaired supply in the future.
:::::::::::::
:::::::::::::Confirm that I did send you additionals / surplus at that time.
:::::::::::::
:::::::::::::BTW… a units banded end would be a 4007’s cathode….or the one that would end up making connection to the 7Y4 cathode, while its free anode end would be the sampling end of the tubes plate pins.
:::::::::::::
:::::::::::::BTW…parte deux…. Take a 9V battery and confirm that your metering instrumentation DC mode IS working.
:::::::::::::
:::::::::::::
:::::::::::::
:::::::::::::73's de Edd
:::::::::::::
:::::::::::::
:::::::::::::
:::::::::::::
:::::::::::::
:::::::::::::
:::::::::::::
:::::::::::::
:::::::::::::::Job,
:::::::::::::::
:::::::::::::::One more check would be to reference your meter minus lead to the centertap wire of the highvoltage winding and measure pin 7 of the 7Y4. If still no voltage I would suspect the 7Y4 is bad or resistors 55 or 56 may open when load is applied. One thing you can do is to substitute a couple of solid state silicon diodes in place of the 7Y4 tube's diodes. A couple of 1N4007 soldered across the socket pins. The anode of each diode to pin 3 or 6 and both cathodes (bar/stripe marking) to pin 7. Of course you will have the 7Y4 unplugged. If you have a variac, you can slowly bring up the line voltage and measure the DC voltage on pin 7 of the tube socket. Or you could have a light bulb in series with the radio line cord. This just in case something goes wrong and would protect the radio.
:::::::::::::::
:::::::::::::::Radiodoc
:::::::::::::::**********
::::::::::::::Job,
::::::::::::::
::::::::::::::One correction to my last post. Even if resistors 55 or 56 were open, referencing your meter to the centertap, you should still measure DC voltage.
::::::::::::::
::::::::::::::Radiodoc
::::::::::::::**********
::::::::::::::
::::::::::::::
:::::::::::::::
:::::::::::::::
::::::::::::::::Gentlemen----I have done some rechecking of voltages and resistance but there is nothing new to report. Doc, there is no DC voltage from pin 7 (cathode) of tube 7Y4 to chassis ground...so, confirming that there can't be any B+ I guess. What I can't wrap around my small brain is why I'm getting proper resistance but no DC voltage...or it seems to me that I'm getting proper resistance... I don't have a spare 7Y4 tube to replace but I did replace the 7B5 tube just in case something was wrong with it.
::::::::::::::::I'm afraid when this exercise is finished I could have egg on my face because it is probably something so simple and I'm just not picking it up.....Everyone have a plesant weekend.
::::::::::::::::Regards
::::::::::::::::
::::::::::::::::
::::::::::::::::
::::::::::::::::
:::::::::::::::::Thanks for your input gentlemen and I certainly have a clearer understanding of troubleshooting the power supply which has a power transformer. It appears that we have come to the conclusion that the power supply is functioning ok?? Please correct me if I’m wrong, but all resistance readings do seem to be in range. However, there is still no B plus voltage readings.....do this mean that there could be a short in the circuit between tube 7B5 and tube XXL? Is there a systematic method of finding a short in the different stages? I’m mystified as to why I’m not getting B plus power.
:::::::::::::::::Regards
:::::::::::::::::
:::::::::::::::::
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::::::::::::::::::Job you got the answer. Good too. And my "nor the negative of ecap 57" means it does not go to ground. As noted, you have negative of cap 57, center tap of power transformer, a 1 meg resistor from pin 6 of 7B5, all connected to a terminal tie point with the 220 ohm resistor.
::::::::::::::::::Bill
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:::::::::::::::::::Gentlemen-------I have more information for you and we’ll see where it leads. First, pin 7, tube 7Y4 to pin 3, tube 7B5 has a resistance of 1733 ohms. Secondly, measuring from pin 2 to pin 3 of tube 7B5 gives a resistance of 697 ohms. Bill, you mentioned that the centre tap of power transformer don’t go to ground or to negative of ecap 57......where do it go??? I have already learnt things from this exercise so keep it up guys.
:::::::::::::::::::Regards
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::::::::::::::::::::Check the center tap of transformer, it does not go to ground, nor the negative of ecap 57.
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::::::::::::::::::::Bill
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:::::::::::::::::::::Job,
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:::::::::::::::::::::Also you should measure around 1700 - 2000 Ohms resistance from pin 7 of the 7Y4 to pin 3 of the 7B5. If not, then perhaps the field coil is open or a bad connection in the wiring. That would account for no voltage on the plates and screens of the other tubes.
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:::::::::::::::::::::Radiodoc
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:::::::::::::::::::::::Hi Job
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::::::::::::::::::::::: You should have resistance between pins #2 and #3 of your 7B5 unless the output transformer is open. This still doesn't explain lack of voltage. Unless the meter was on AC and wouldn't read DC voltage?
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:::::::::::::::::::::::Norm
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::::::::::::::::::::::::Gentlemen.......Thank you for your advise and suggestions......I retested the 7Y4 tube and it’s ok..checked resistors 55 and 56 also ok..checked the three caps removed, no shorts detected..I also checked resistors throughout the radio, plus checked circuits for shorts..everything seemed ok. However there is one thing, there is no resistance between pins 2 and 3 0f tube 7B5. Shouldn’t I be picking up resistance across primary of output transformer when measuring between these two points??? Looking forward to hearing from you.
::::::::::::::::::::::::Regards
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::::::::::::::::::::::::::Hi Bill
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:::::::::::::::::::::::::: Very possible if the tube wasn't tested. I've also found open resistors from transformer center tap to chassis acting this way.
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::::::::::::::::::::::::::Norm
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:::::::::::::::::::::::::::Hi Guys,
::::::::::::::::::::::::::: Looks like a 7Y4 with a detached cathode. What am I missing?
::::::::::::::::::::::::::: If that is it, don't just replace the 7Y4 as there may be a short circuit in the radio that blew out the cathode connection. Check for short circuits and check the electrolytic capacitors you took out. If one was short you have already cleared that problem.
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:::::::::::::::::::::::::::Best Regards,
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:::::::::::::::::::::::::::Bill Grimm
:::::::::::::::::::::::::Hi Norm,
::::::::::::::::::::::::: I agree. That will do it, too.
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:::::::::::::::::::::::::All the Best,
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:::::::::::::::::::::::::Bill
::::::::::::::::::::::Hi Job and Norm,
:::::::::::::::::::::: Consider the possibility that the speaker, field coil and all are not wired into the circuit properly. That would explain the open between pins 2 and 3 on the 7B5, and the no B+.
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::::::::::::::::::::::All the Best,
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::::::::::::::::::::::Bill Grimm