Checked the 42 tube and 75 tube voltages as you suggested and here are the results, readings are from pin 1 around the base to pin 6. In that the results seem strange I tested each one several time to make sure my reading were correct:
Tube Pin # Specified voltage Actual voltage
# 42 1 0 0
2 243 0
3 258 129
4 0 0
5 0 0
6 0 6
75 1 0 0
2 0 153
3 129 0
4 0 0
5 0 0
6 0 6
As you can see there is a problem but I have no idea what the problem is or what is causing it. Further, when I turn he set on there is only a loud hum which fades to a quiet hum after about 3-5 minutes. Please, what ever help you can provide is greatly appreciated.
Tube # 42
Pine #
1 0v 0v
2 243v 0v
3 258v 129v
4 0v 0v
5 0v 0v
6 0v 6v
Tube 75
Pine #
1 0v 0v
2 0v 129v
3 129v 0v
4 0v 0v
5 0v 0v
6 0v 6v
The first voltage is what it should be, the second one is what is is presently reading. Hope you can read this chart
:Guys:
:
:Checked the 42 tube and 75 tube voltages as you suggested and here are the results, readings are from pin 1 around the base to pin 6. In that the results seem strange I tested each one several time to make sure my reading were correct:
:
:Tube Pin # Specified voltage Actual voltage
:# 42 1 0 0
: 2 243 0
: 3 258 129
: 4 0 0
: 5 0 0
: 6 0 6
:
:75 1 0 0
: 2 0 153
: 3 129 0
: 4 0 0
: 5 0 0
: 6 0 6
:
:As you can see there is a problem but I have no idea what the problem is or what is causing it. Further, when I turn he set on there is only a loud hum which fades to a quiet hum after about 3-5 minutes. Please, what ever help you can provide is greatly appreciated.
:
:
:Tube # 42
:
:Pine #
:
:1 0v 0v
:2 243v 0v
:3 258v 129v
:4 0v 0v
:5 0v 0v
:6 0v 6v
:
:Tube 75
:
:Pine #
:1 0v 0v
:2 0v 129v
:3 129v 0v
:4 0v 0v
:5 0v 0v
:6 0v 6v
:
:The first voltage is what it should be, the second one is what is is presently reading. Hope you can read this chart
Dave: There is something very much funny here. On the type 75, pins 3 and 4 are tied together, and should read exactly the same.
The zero Volts on the plate of the type 42 indicates a short in the plate circuit. How many Ohms does ya got from pin 2 of the 42 to ground???
Lewis
Philco 620 has capacitors (61 & 61A) from the plate of the 42 tube to ground. Since overall voltage is low and plate is zero one or more of these caps may be shorted?
You 75 tube voltage is ok. Pin #2 is plate and should be positive.
Norm
http://www.nostalgiaair.org/PagesByModel/804/M0013804.pdf
::My chart did not come out right when I posted the message so here it is in another format
::
::Tube # 42
::
::Pine #
::
::1 0v 0v
::2 243v 0v
::3 258v 129v
::4 0v 0v
::5 0v 0v
::6 0v 6v
::
::Tube 75
::
::Pine #
::1 0v 0v
::2 0v 129v
::3 129v 0v
::4 0v 0v
::5 0v 0v
::6 0v 6v
::
::The first voltage is what it should be, the second one is what is is presently reading. Hope you can read this chart
:
:
:
:Dave: There is something very much funny here. On the type 75, pins 3 and 4 are tied together, and should read exactly the same.
:
:The zero Volts on the plate of the type 42 indicates a short in the plate circuit. How many Ohms does ya got from pin 2 of the 42 to ground???
:Lewis
:
: Philco 620 has capacitors (61 & 61A) from the plate of the 42 tube to ground. Since overall voltage is low and plate is zero one or more of these caps may be shorted?
:
: You 75 tube voltage is ok. Pin #2 is plate and should be positive.
YOu can check part #61 really quick by moving the tone control away from the "bass" position.
Lewis
:
:Norm
:
: http://www.nostalgiaair.org/PagesByModel/804/M0013804.pdf
:
:
:::My chart did not come out right when I posted the message so here it is in another format
:::
:::Tube # 42
:::
:::Pine #
:::
:::1 0v 0v
:::2 243v 0v
:::3 258v 129v
:::4 0v 0v
:::5 0v 0v
:::6 0v 6v
:::
:::Tube 75
:::
:::Pine #
:::1 0v 0v
:::2 0v 129v
:::3 129v 0v
:::4 0v 0v
:::5 0v 0v
:::6 0v 6v
:::
:::The first voltage is what it should be, the second one is what is is presently reading. Hope you can read this chart
::
::
::
::Dave: There is something very much funny here. On the type 75, pins 3 and 4 are tied together, and should read exactly the same.
::
::The zero Volts on the plate of the type 42 indicates a short in the plate circuit. How many Ohms does ya got from pin 2 of the 42 to ground???
::Lewis
::
:: Philco 620 has capacitors (61 & 61A) from the plate of the 42 tube to ground. Since overall voltage is low and plate is zero one or more of these caps may be shorted?
Hey, another thing we hope isn't is the field coil for the speaker may be shorted to the frame. If so, it might be easily fixable and it may be BAD news.
Lewis
I will check it out and let you know, but above all I want to thank you for getting back to me
:::Hi
:::
::: Philco 620 has capacitors (61 & 61A) from the plate of the 42 tube to ground. Since overall voltage is low and plate is zero one or more of these caps may be shorted?
:
:
:Hey, another thing we hope isn't is the field coil for the speaker may be shorted to the frame. If so, it might be easily fixable and it may be BAD news.
:Lewis
Norm: the 61A 302K cap was repalced new. I just found the cap inside the tone control it's a .01 or 103K Sparague and looks real old. I don't hace a 103K cap but have some 145K and higher, will they do as a repalcement. On caps, can't you replace with a higher value but never a lower? Needs to say I will replace the cap and try again.
Lewis: the ohm reading between pin 2 and ground of tube 42 is 2.5
I will replace the cap and some of the ratty wires and try it again.
:Guys:
:
:I will check it out and let you know, but above all I want to thank you for getting back to me
:
:
::::Hi
::::
:::: Philco 620 has capacitors (61 & 61A) from the plate of the 42 tube to ground. Since overall voltage is low and plate is zero one or more of these caps may be shorted?
::
::
::Hey, another thing we hope isn't is the field coil for the speaker may be shorted to the frame. If so, it might be easily fixable and it may be BAD news.
::Lewis
:
:Norm: the 61A 302K cap was repalced new. I just found the cap inside the tone control it's a .01 or 103K Sparague and looks real old. I don't hace a 103K cap but have some 145K and higher, will they do as a repalcement. On caps, can't you replace with a higher value but never a lower? Needs to say I will replace the cap and try again.
Dave:
In the case of the tone control, disconnect one leg for now and let it go. It only cuts the high frequencies of the audio to give more bass.
:
:Lewis: the ohm reading between pin 2 and ground of tube 42 is 2.5
Man, that is WAY wrong, I am assuming you mean Ohms, not kOhms, but now you are in the right direction. Now you have to go through the tedious and unpleasant jot of disconnecting things and taking Ohmmeter readings until you find where the short is.
Lewis
:
:I will replace the cap and some of the ratty wires and try it again.
:
:
:
:
:
::Guys:
::
::I will check it out and let you know, but above all I want to thank you for getting back to me
::
::
:::::Hi
:::::
::::: Philco 620 has capacitors (61 & 61A) from the plate of the 42 tube to ground. Since overall voltage is low and plate is zero one or more of these caps may be shorted?
:::
:::
:::Hey, another thing we hope isn't is the field coil for the speaker may be shorted to the frame. If so, it might be easily fixable and it may be BAD news.
:::Lewis
Disconnect what, where do I start, But could it not be the tone control in that it all relates to the circuit? Should I not disconnect or repair the tone control first and see what happens? Norm, what's your thoughts? Can I replace the 103K cap with a high value or not? So you know, I know very little about electronics and even less about radio repairs. What I know I am learning from you guys, so please be patient. Thanks for the help, I will keep you posted. Have a blessed New Year
Dave
Disconnect wires on your 42 tube, pin #2, plate, until the 2.5 ohm resistance reading to ground is gone.
You don't need the tone control connected for your radio to operate. Some Philco tone capacitors are in metal cans. May have a short between the can and lead?
Don't use a 145K in place of 103K cap. A 103 is .01 mf. A 145 would be 1.4 mf, more than 100 times greater. Higher capacity will reduce high frequency response. A capacitor this great will probably eliminate all sound.
For bypass caps values can be greatly increased. On signal lines frequency response will be effected.
Norm
:Lewis:
:
:Disconnect what, where do I start, But could it not be the tone control in that it all relates to the circuit? Should I not disconnect or repair the tone control first and see what happens? Norm, what's your thoughts? Can I replace the 103K cap with a high value or not? So you know, I know very little about electronics and even less about radio repairs. What I know I am learning from you guys, so please be patient. Thanks for the help, I will keep you posted. Have a blessed New Year
:
:
:Dave
:
:
PTL, the radio is working again, it seems to have been the tone control, I replaced the capacitor wit the required 103K and it's good on one of the three settings but the other two settings produce a loud squealing sound and only minimum volume. In light of this we seem to be going again but there is not a lot of power on the volume control which also crackles alot. I'm going to spray it with contact cleaner to see if it clears it up.
My friends, I can't tell you how much I appreciate your time and effort, again you are teaching me a lot. I will continue to need your help, and I'm glad your always there, thank you, thank you, thank you.
Dave
:Dave
:
: Disconnect wires on your 42 tube, pin #2, plate, until the 2.5 ohm resistance reading to ground is gone.
:
: You don't need the tone control connected for your radio to operate. Some Philco tone capacitors are in metal cans. May have a short between the can and lead?
:
: Don't use a 145K in place of 103K cap. A 103 is .01 mf. A 145 would be 1.4 mf, more than 100 times greater. Higher capacity will reduce high frequency response. A capacitor this great will probably eliminate all sound.
:
: For bypass caps values can be greatly increased. On signal lines frequency response will be effected.
:
: Norm
:
::Lewis:
::
::Disconnect what, where do I start, But could it not be the tone control in that it all relates to the circuit? Should I not disconnect or repair the tone control first and see what happens? Norm, what's your thoughts? Can I replace the 103K cap with a high value or not? So you know, I know very little about electronics and even less about radio repairs. What I know I am learning from you guys, so please be patient. Thanks for the help, I will keep you posted. Have a blessed New Year
::
::
::Dave
::
::
:
:Disconnect what, where do I start, But could it not be the tone control in that it all relates to the circuit? Should I not disconnect or repair the tone control first and see what happens? Norm, what's your thoughts? Can I replace the 103K cap with a high value or not?
Dave:
The cap in the tone control circuit must be replaced by the same value, but doesn't have to be in the circuit for the radio to work. It simply bypasses some of the high audio frequencies to ground for more bass in the output. Clip one lead of it for now and replace it when you don't have more important things to worry about.
Lewis
Dave …Dave …which Dave….’ya gotta have a program to identify the Dave…but possibly, this is Preacher Dave
Looking at the thumbnail provided of the 620 I was hard pressed to find any .01’s in the audio circuitry. I circled the item numbers and they were a covey of .02 ufds.
Starting with an .02 item / #42 coming off with the detected audio from the 75 and being fed into the high end of the volume control. Then the audio comes off from the wiper of the volume control and is fed thru .02 item / #43 , which feeds to the 1st grid(cap) of the 75. The amplified audio is taken off at the plate of the 75 and then feeds into the 1st grid of the #42 output tube thru .02 item / #59.
Where is the .01 ufd ???
Referencing your voltages given, the voltages fall within reason on the 75, with the exception that there must be an error in data gathering, as the two diode plates are connected together on pins 3 & 4 , yet you show an outrageously high voltage on one diode detector plate….in error assuredly.
Now, in referencing the marked up schema, and looking at the B+ flow of the dotted red lines coming up from the power supply up to feed the #42, there is an initial passage thru the field coil of the speaker and then the point where the reduced B+ feed out of the field coil branches out and is fed up to the screen grid of the 42, the B+ supply side of the output transformer and downwards thru the dotted orange supply line to feed the balance of the set AND the 75’s audio plate supply.
Your figures establish that voltage as being 129VDC ( assuredly being pulled down by heavy loading) with the # 42's plate voltage being circa zilch. So probably what has happened was that the set has defective / shorted item # 61 .02 capacitor , and you have somehow ended up with the tone control / switch being in that third position and the # 42 plate is being shorted to ground thru that capacitor.
Normally, the first tone position has no effect, the second position shunts capacitor Item # 46 to effect a tonal change by shorting that .02 capacitor of a series RC network with its associated resistor item # 45. Those two RC components are the constituents of a loudness compensation circuit that is tied into that 225,000 k tap that you see on the lower portion of the volume control.
At the lower positions of the volume control, it enhances the human ears perceived bass response at low volume levels, by slight treble attenuation , up to the threshold where the wiper passes onto that tap point. Or when you flip that tone adjustment to the mid position, and alter the tonal response in that manner.
The third position of the tone control is where item # 61 / .02 ufd cap bypasses high audio frequencies on the plate circuit to ground. The third being the position of the most treble attenuation…..ergo….. most perceived bass enhancement..
Considering yourself to find that unit to be shorted , its replacement with a disc ceramic unit of .02 ufd @ 1KV + voltage rating should probably give a reliability half life of a millennium.
Tech Referencing Markup Schema:
73's de Edd
::Lewis:
::
::Disconnect what, where do I start, But could it not be the tone control in that it all relates to the circuit? Should I not disconnect or repair the tone control first and see what happens? Norm, what's your thoughts? Can I replace the 103K cap with a high value or not?
:
:Dave:
:The cap in the tone control circuit must be replaced by the same value, but doesn't have to be in the circuit for the radio to work. It simply bypasses some of the high audio frequencies to ground for more bass in the output. Clip one lead of it for now and replace it when you don't have more important things to worry about.
:Lewis
remember when he wrote this line?
"Lewis: the ohm reading between pin 2 and ground of tube 42 is 2.5"
I say we go the pin 2 of the type 42 and start disconnecting stuff until the Ohmmeter reading goes up considerably.
Lewis
:
:
:
:
:Dave …Dave …which Dave….’ya gotta have a program to identify the Dave…but possibly, this is Preacher Dave
:
:Looking at the thumbnail provided of the 620 I was hard pressed to find any .01’s in the audio circuitry. I circled the item numbers and they were a covey of .02 ufds.
:
:Starting with an .02 item / #42 coming off with the detected audio from the 75 and being fed into the high end of the volume control. Then the audio comes off from the wiper of the volume control and is fed thru .02 item / #43 , which feeds to the 1st grid(cap) of the 75. The amplified audio is taken off at the plate of the 75 and then feeds into the 1st grid of the #42 output tube thru .02 item / #59.
:Where is the .01 ufd ???
:Referencing your voltages given, the voltages fall within reason on the 75, with the exception that there must be an error in data gathering, as the two diode plates are connected together on pins 3 & 4 , yet you show an outrageously high voltage on one diode detector plate….in error assuredly.
: Now, in referencing the marked up schema, and looking at the B+ flow of the dotted red lines coming up from the power supply up to feed the #42, there is an initial passage thru the field coil of the speaker and then the point where the reduced B+ feed out of the field coil branches out and is fed up to the screen grid of the 42, the B+ supply side of the output transformer and downwards thru the dotted orange supply line to feed the balance of the set AND the 75’s audio plate supply.
: Your figures establish that voltage as being 129VDC ( assuredly being pulled down by heavy loading) with the # 42's plate voltage being circa zilch. So probably what has happened was that the set has defective / shorted item # 61 .02 capacitor , and you have somehow ended up with the tone control / switch being in that third position and the # 42 plate is being shorted to ground thru that capacitor.
:
:Normally, the first tone position has no effect, the second position shunts capacitor Item # 46 to effect a tonal change by shorting that .02 capacitor of a series RC network with its associated resistor item # 45. Those two RC components are the constituents of a loudness compensation circuit that is tied into that 225,000 k tap that you see on the lower portion of the volume control.
:At the lower positions of the volume control, it enhances the human ears perceived bass response at low volume levels, by slight treble attenuation , up to the threshold where the wiper passes onto that tap point. Or when you flip that tone adjustment to the mid position, and alter the tonal response in that manner.
:The third position of the tone control is where item # 61 / .02 ufd cap bypasses high audio frequencies on the plate circuit to ground. The third being the position of the most treble attenuation…..ergo….. most perceived bass enhancement..
:
:Considering yourself to find that unit to be shorted , its replacement with a disc ceramic unit of .02 ufd @ 1KV + voltage rating should probably give a reliability half life of a millennium.
:
:Tech Referencing Markup Schema:
:
:
:
:
:
:73's de Edd
:
:
:
:
:
:::Lewis:
:::
:::Disconnect what, where do I start, But could it not be the tone control in that it all relates to the circuit? Should I not disconnect or repair the tone control first and see what happens? Norm, what's your thoughts? Can I replace the 103K cap with a high value or not?
::
::Dave:
::The cap in the tone control circuit must be replaced by the same value, but doesn't have to be in the circuit for the radio to work. It simply bypasses some of the high audio frequencies to ground for more bass in the output. Clip one lead of it for now and replace it when you don't have more important things to worry about.
::Lewis
My vote is for cap 61A. It is in the plate circuit to ground/chassis regardless of the position of the tone switch. I don't see where he got 2.5 Ohms, but I do see where one could measure 25 or so Ohms from plate to chassis/ground if cap 61A were shorted. The 25 Or so Ohms would be the measured value of the resistor(s) from the HV centertap to chassis/ground.
Radiodoc
**********
::Sir Eddward:
:remember when he wrote this line?
:
:"Lewis: the ohm reading between pin 2 and ground of tube 42 is 2.5"
:
:I say we go the pin 2 of the type 42 and start disconnecting stuff until the Ohmmeter reading goes up considerably.
:Lewis
::
::
::
::
::Dave …Dave …which Dave….’ya gotta have a program to identify the Dave…but possibly, this is Preacher Dave
::
::Looking at the thumbnail provided of the 620 I was hard pressed to find any .01’s in the audio circuitry. I circled the item numbers and they were a covey of .02 ufds.
::
::Starting with an .02 item / #42 coming off with the detected audio from the 75 and being fed into the high end of the volume control. Then the audio comes off from the wiper of the volume control and is fed thru .02 item / #43 , which feeds to the 1st grid(cap) of the 75. The amplified audio is taken off at the plate of the 75 and then feeds into the 1st grid of the #42 output tube thru .02 item / #59.
::Where is the .01 ufd ???
::Referencing your voltages given, the voltages fall within reason on the 75, with the exception that there must be an error in data gathering, as the two diode plates are connected together on pins 3 & 4 , yet you show an outrageously high voltage on one diode detector plate….in error assuredly.
:: Now, in referencing the marked up schema, and looking at the B+ flow of the dotted red lines coming up from the power supply up to feed the #42, there is an initial passage thru the field coil of the speaker and then the point where the reduced B+ feed out of the field coil branches out and is fed up to the screen grid of the 42, the B+ supply side of the output transformer and downwards thru the dotted orange supply line to feed the balance of the set AND the 75’s audio plate supply.
:: Your figures establish that voltage as being 129VDC ( assuredly being pulled down by heavy loading) with the # 42's plate voltage being circa zilch. So probably what has happened was that the set has defective / shorted item # 61 .02 capacitor , and you have somehow ended up with the tone control / switch being in that third position and the # 42 plate is being shorted to ground thru that capacitor.
::
::Normally, the first tone position has no effect, the second position shunts capacitor Item # 46 to effect a tonal change by shorting that .02 capacitor of a series RC network with its associated resistor item # 45. Those two RC components are the constituents of a loudness compensation circuit that is tied into that 225,000 k tap that you see on the lower portion of the volume control.
::At the lower positions of the volume control, it enhances the human ears perceived bass response at low volume levels, by slight treble attenuation , up to the threshold where the wiper passes onto that tap point. Or when you flip that tone adjustment to the mid position, and alter the tonal response in that manner.
::The third position of the tone control is where item # 61 / .02 ufd cap bypasses high audio frequencies on the plate circuit to ground. The third being the position of the most treble attenuation…..ergo….. most perceived bass enhancement..
::
::Considering yourself to find that unit to be shorted , its replacement with a disc ceramic unit of .02 ufd @ 1KV + voltage rating should probably give a reliability half life of a millennium.
::
::Tech Referencing Markup Schema:
::
::
::
::
::
::73's de Edd
::
::
::
::
::
::::Lewis:
::::
::::Disconnect what, where do I start, But could it not be the tone control in that it all relates to the circuit? Should I not disconnect or repair the tone control first and see what happens? Norm, what's your thoughts? Can I replace the 103K cap with a high value or not?
:::
:::Dave:
:::The cap in the tone control circuit must be replaced by the same value, but doesn't have to be in the circuit for the radio to work. It simply bypasses some of the high audio frequencies to ground for more bass in the output. Clip one lead of it for now and replace it when you don't have more important things to worry about.
:::Lewis
Lewis
Should we perhaps say a little prayer that the short on the plate has not burned open the 400 Ohm primary of the output transformer?
Radiodoc
**********
:Radiodoc, I agree completely. He said he is not real familiar with test equipment, and may be reading on a X10 scale, which would put the spotlight on your suspect. Let's hope, otherwise the field coil may be shorted, but what the heck, we can talk him through that, too, can we not?
:Lewis
Norm
:Lewis L.,
:
:Should we perhaps say a little prayer that the short on the plate has not burned open the 400 Ohm primary of the output transformer?
:
:Radiodoc
:**********
:
:
::Radiodoc, I agree completely. He said he is not real familiar with test equipment, and may be reading on a X10 scale, which would put the spotlight on your suspect. Let's hope, otherwise the field coil may be shorted, but what the heck, we can talk him through that, too, can we not?
::Lewis
PTL, the radio is working again. Thank you for your suggestion of a "little prayer" because the Lord said "little is much" Your prayers were answered. The problem seems to have been the cap in the tone control, a 103K that was replaced once before in the radios life in that it was not a Philco cap rather a Spargue cap. I replaced the cap and one setting is real quiet and works well, the other two produce a squealing sound. There is not a lot of volume to it, I have to recone the speaker in that the paper is torn. I have another cap to replace, it's a 30-4017 which is not on the parts list. This cap is a .1 or 104K cap.
There is another cap that was put in at some point in the radios history in that the part 67 condenser an
8 mfd & 8 mfd was replaced with a Connell BVB 1145, 10-10 mfd cap with two leads on one side and one on the other, My cap kit I bought has two blue colored 10uf caps that are probably to replace this one cap, does this sound right? Further there is another cap, part # 52, that should probably be replaced, the kit has a blue 16 uf apparently to replace it? Should I replace these or leave them alone in that the radio is working?
Guys, what one book can you suggest that would help a novice like me diagnose and repair these radios?
Finally, all of you have been an answer to prayer Matt 7:7 "seek, and ye shall find; knock, and it shall be opened unto you:" you are a tremendous help!
Dave B.
:It hasn't so far burned open the output transformer. Due to the plate being shorted all voltages are low. Looks like there is 129 volts across the winding.
:
:Norm
:
::Lewis L.,
::
::Should we perhaps say a little prayer that the short on the plate has not burned open the 400 Ohm primary of the output transformer?
::
::Radiodoc
::**********
::
::
:::Radiodoc, I agree completely. He said he is not real familiar with test equipment, and may be reading on a X10 scale, which would put the spotlight on your suspect. Let's hope, otherwise the field coil may be shorted, but what the heck, we can talk him through that, too, can we not?
:::Lewis
Thank you for getting back, your information and schematic, there fantastic. For now on I will identify myself as Dave B. It will take me a while to digest the information so I will advise. But, PTL the radio is working again it seems to have been the tone control. But two of the three positions produce a squeal along with it, the other one position is good and quiet I have one more capacitor to replace the 30-4017 cap, a .1 or 104K I can not find a 30-4017 list in the parts section but it's the capacitor that is in place.
Edd, can you think of a single book that might really help a novice like me understand how to diagnose and repair these radios? Everything is new to me and I have a few radios I would really like to repair. Again, thank you Edd you are a tremendous help and a blessing.
Yours humbly
Dave B, or Preacher Dave
:
:
:
:
:Dave …Dave …which Dave….’ya gotta have a program to identify the Dave…but possibly, this is Preacher Dave
:
:Looking at the thumbnail provided of the 620 I was hard pressed to find any .01’s in the audio circuitry. I circled the item numbers and they were a covey of .02 ufds.
:
:Starting with an .02 item / #42 coming off with the detected audio from the 75 and being fed into the high end of the volume control. Then the audio comes off from the wiper of the volume control and is fed thru .02 item / #43 , which feeds to the 1st grid(cap) of the 75. The amplified audio is taken off at the plate of the 75 and then feeds into the 1st grid of the #42 output tube thru .02 item / #59.
:Where is the .01 ufd ???
:Referencing your voltages given, the voltages fall within reason on the 75, with the exception that there must be an error in data gathering, as the two diode plates are connected together on pins 3 & 4 , yet you show an outrageously high voltage on one diode detector plate….in error assuredly.
: Now, in referencing the marked up schema, and looking at the B+ flow of the dotted red lines coming up from the power supply up to feed the #42, there is an initial passage thru the field coil of the speaker and then the point where the reduced B+ feed out of the field coil branches out and is fed up to the screen grid of the 42, the B+ supply side of the output transformer and downwards thru the dotted orange supply line to feed the balance of the set AND the 75’s audio plate supply.
: Your figures establish that voltage as being 129VDC ( assuredly being pulled down by heavy loading) with the # 42's plate voltage being circa zilch. So probably what has happened was that the set has defective / shorted item # 61 .02 capacitor , and you have somehow ended up with the tone control / switch being in that third position and the # 42 plate is being shorted to ground thru that capacitor.
:
:Normally, the first tone position has no effect, the second position shunts capacitor Item # 46 to effect a tonal change by shorting that .02 capacitor of a series RC network with its associated resistor item # 45. Those two RC components are the constituents of a loudness compensation circuit that is tied into that 225,000 k tap that you see on the lower portion of the volume control.
:At the lower positions of the volume control, it enhances the human ears perceived bass response at low volume levels, by slight treble attenuation , up to the threshold where the wiper passes onto that tap point. Or when you flip that tone adjustment to the mid position, and alter the tonal response in that manner.
:The third position of the tone control is where item # 61 / .02 ufd cap bypasses high audio frequencies on the plate circuit to ground. The third being the position of the most treble attenuation…..ergo….. most perceived bass enhancement..
:
:Considering yourself to find that unit to be shorted , its replacement with a disc ceramic unit of .02 ufd @ 1KV + voltage rating should probably give a reliability half life of a millennium.
:
:Tech Referencing Markup Schema:
:
:
:
:
:
:73's de Edd
:
:
:
:
:
:::Lewis:
:::
:::Disconnect what, where do I start, But could it not be the tone control in that it all relates to the circuit? Should I not disconnect or repair the tone control first and see what happens? Norm, what's your thoughts? Can I replace the 103K cap with a high value or not?
::
::Dave:
::The cap in the tone control circuit must be replaced by the same value, but doesn't have to be in the circuit for the radio to work. It simply bypasses some of the high audio frequencies to ground for more bass in the output. Clip one lead of it for now and replace it when you don't have more important things to worry about.
::Lewis
There is some good information on this site under References.
Radiodoc
**********
:Edd
:
:Thank you for getting back, your information and schematic, there fantastic. For now on I will identify myself as Dave B. It will take me a while to digest the information so I will advise. But, PTL the radio is working again it seems to have been the tone control. But two of the three positions produce a squeal along with it, the other one position is good and quiet I have one more capacitor to replace the 30-4017 cap, a .1 or 104K I can not find a 30-4017 list in the parts section but it's the capacitor that is in place.
:
:Edd, can you think of a single book that might really help a novice like me understand how to diagnose and repair these radios? Everything is new to me and I have a few radios I would really like to repair. Again, thank you Edd you are a tremendous help and a blessing.
:
:Yours humbly
:
:Dave B, or Preacher Dave
::
::
::
::
::Dave …Dave …which Dave….’ya gotta have a program to identify the Dave…but possibly, this is Preacher Dave
::
::Looking at the thumbnail provided of the 620 I was hard pressed to find any .01’s in the audio circuitry. I circled the item numbers and they were a covey of .02 ufds.
::
::Starting with an .02 item / #42 coming off with the detected audio from the 75 and being fed into the high end of the volume control. Then the audio comes off from the wiper of the volume control and is fed thru .02 item / #43 , which feeds to the 1st grid(cap) of the 75. The amplified audio is taken off at the plate of the 75 and then feeds into the 1st grid of the #42 output tube thru .02 item / #59.
::Where is the .01 ufd ???
::Referencing your voltages given, the voltages fall within reason on the 75, with the exception that there must be an error in data gathering, as the two diode plates are connected together on pins 3 & 4 , yet you show an outrageously high voltage on one diode detector plate….in error assuredly.
:: Now, in referencing the marked up schema, and looking at the B+ flow of the dotted red lines coming up from the power supply up to feed the #42, there is an initial passage thru the field coil of the speaker and then the point where the reduced B+ feed out of the field coil branches out and is fed up to the screen grid of the 42, the B+ supply side of the output transformer and downwards thru the dotted orange supply line to feed the balance of the set AND the 75’s audio plate supply.
:: Your figures establish that voltage as being 129VDC ( assuredly being pulled down by heavy loading) with the # 42's plate voltage being circa zilch. So probably what has happened was that the set has defective / shorted item # 61 .02 capacitor , and you have somehow ended up with the tone control / switch being in that third position and the # 42 plate is being shorted to ground thru that capacitor.
::
::Normally, the first tone position has no effect, the second position shunts capacitor Item # 46 to effect a tonal change by shorting that .02 capacitor of a series RC network with its associated resistor item # 45. Those two RC components are the constituents of a loudness compensation circuit that is tied into that 225,000 k tap that you see on the lower portion of the volume control.
::At the lower positions of the volume control, it enhances the human ears perceived bass response at low volume levels, by slight treble attenuation , up to the threshold where the wiper passes onto that tap point. Or when you flip that tone adjustment to the mid position, and alter the tonal response in that manner.
::The third position of the tone control is where item # 61 / .02 ufd cap bypasses high audio frequencies on the plate circuit to ground. The third being the position of the most treble attenuation…..ergo….. most perceived bass enhancement..
::
::Considering yourself to find that unit to be shorted , its replacement with a disc ceramic unit of .02 ufd @ 1KV + voltage rating should probably give a reliability half life of a millennium.
::
::Tech Referencing Markup Schema:
::
::
::
::
::
::73's de Edd
::
::
::
::
::
::::Lewis:
::::
::::Disconnect what, where do I start, But could it not be the tone control in that it all relates to the circuit? Should I not disconnect or repair the tone control first and see what happens? Norm, what's your thoughts? Can I replace the 103K cap with a high value or not?
:::
:::Dave:
:::The cap in the tone control circuit must be replaced by the same value, but doesn't have to be in the circuit for the radio to work. It simply bypasses some of the high audio frequencies to ground for more bass in the output. Clip one lead of it for now and replace it when you don't have more important things to worry about.
:::Lewis
:Dave B.,
:
:There is some good information on this site under References.
:
:Radiodoc
:**********
:
:
::Edd
::
::Thank you for getting back, your information and schematic, there fantastic. For now on I will identify myself as Dave B. It will take me a while to digest the information so I will advise. But, PTL the radio is working again it seems to have been the tone control. But two of the three positions produce a squeal along with it, the other one position is good and quiet I have one more capacitor to replace the 30-4017 cap, a .1 or 104K I can not find a 30-4017 list in the parts section but it's the capacitor that is in place.
::
::Edd, can you think of a single book that might really help a novice like me understand how to diagnose and repair these radios? Everything is new to me and I have a few radios I would really like to repair. Again, thank you Edd you are a tremendous help and a blessing.
::
::Yours humbly
::
::Dave B, or Preacher Dave
:::
:::
:::
:::
:::Dave …Dave …which Dave….’ya gotta have a program to identify the Dave…but possibly, this is Preacher Dave
:::
:::Looking at the thumbnail provided of the 620 I was hard pressed to find any .01’s in the audio circuitry. I circled the item numbers and they were a covey of .02 ufds.
:::
:::Starting with an .02 item / #42 coming off with the detected audio from the 75 and being fed into the high end of the volume control. Then the audio comes off from the wiper of the volume control and is fed thru .02 item / #43 , which feeds to the 1st grid(cap) of the 75. The amplified audio is taken off at the plate of the 75 and then feeds into the 1st grid of the #42 output tube thru .02 item / #59.
:::Where is the .01 ufd ???
:::Referencing your voltages given, the voltages fall within reason on the 75, with the exception that there must be an error in data gathering, as the two diode plates are connected together on pins 3 & 4 , yet you show an outrageously high voltage on one diode detector plate….in error assuredly.
::: Now, in referencing the marked up schema, and looking at the B+ flow of the dotted red lines coming up from the power supply up to feed the #42, there is an initial passage thru the field coil of the speaker and then the point where the reduced B+ feed out of the field coil branches out and is fed up to the screen grid of the 42, the B+ supply side of the output transformer and downwards thru the dotted orange supply line to feed the balance of the set AND the 75’s audio plate supply.
::: Your figures establish that voltage as being 129VDC ( assuredly being pulled down by heavy loading) with the # 42's plate voltage being circa zilch. So probably what has happened was that the set has defective / shorted item # 61 .02 capacitor , and you have somehow ended up with the tone control / switch being in that third position and the # 42 plate is being shorted to ground thru that capacitor.
:::
:::Normally, the first tone position has no effect, the second position shunts capacitor Item # 46 to effect a tonal change by shorting that .02 capacitor of a series RC network with its associated resistor item # 45. Those two RC components are the constituents of a loudness compensation circuit that is tied into that 225,000 k tap that you see on the lower portion of the volume control.
:::At the lower positions of the volume control, it enhances the human ears perceived bass response at low volume levels, by slight treble attenuation , up to the threshold where the wiper passes onto that tap point. Or when you flip that tone adjustment to the mid position, and alter the tonal response in that manner.
:::The third position of the tone control is where item # 61 / .02 ufd cap bypasses high audio frequencies on the plate circuit to ground. The third being the position of the most treble attenuation…..ergo….. most perceived bass enhancement..
:::
:::Considering yourself to find that unit to be shorted , its replacement with a disc ceramic unit of .02 ufd @ 1KV + voltage rating should probably give a reliability half life of a millennium.
:::
:::Tech Referencing Markup Schema:
:::
:::
:::
:::
:::
:::73's de Edd
:::
:::
:::
:::
:::
:::::Lewis:
:::::
:::::Disconnect what, where do I start, But could it not be the tone control in that it all relates to the circuit? Should I not disconnect or repair the tone control first and see what happens? Norm, what's your thoughts? Can I replace the 103K cap with a high value or not?
::::
::::Dave:
::::The cap in the tone control circuit must be replaced by the same value, but doesn't have to be in the circuit for the radio to work. It simply bypasses some of the high audio frequencies to ground for more bass in the output. Clip one lead of it for now and replace it when you don't have more important things to worry about.
::::Lewis
Had a chance to look the schematic over and provide the following information. The .01 Cap is inside part 60, the Tone Control. This cap does not seem to be listed in the parts section or show in the schematic. It was a Spargue cap that seems to have been replaced at some point in the radios history. I replaced it with a .01 cap or a 103K and the control seems to work OK. The other cap, the 30-4017 a .1 cap or 104K was also replaced today and the radio is still OK, but it seems to take about 2 or more minutes to really warm up and become stable.
As mentioned previously, part 67 cap, a 8-8 mfd unit was replaced with a Connell 10-10 cap, the cap having two leads coming off it. As part of a cap kit I purchased for the radio I have two blue 10 ufd caps which are probably to replace this cap, is this correct? Further, I have a single blue 16 uf cap which is probably to replace the part 52, the 16 mfd cap? I also have two square orange colored MKT .015K caps, Edd where do they go, I have no idea, and why are they so different than the rest.
Im' sorry my friend for asking so many questions, but you are a tremendous help. Again thank you for your time and patience.
:Edd
:
:Thank you for getting back, your information and schematic, there fantastic. For now on I will identify myself as Dave B. It will take me a while to digest the information so I will advise. But, PTL the radio is working again it seems to have been the tone control. But two of the three positions produce a squeal along with it, the other one position is good and quiet I have one more capacitor to replace the 30-4017 cap, a .1 or 104K I can not find a 30-4017 list in the parts section but it's the capacitor that is in place.
:
:Edd, can you think of a single book that might really help a novice like me understand how to diagnose and repair these radios? Everything is new to me and I have a few radios I would really like to repair. Again, thank you Edd you are a tremendous help and a blessing.
:
:Yours humbly
:
:Dave B, or Preacher Dave
::
::
::
::
::Dave …Dave …which Dave….’ya gotta have a program to identify the Dave…but possibly, this is Preacher Dave
::
::Looking at the thumbnail provided of the 620 I was hard pressed to find any .01’s in the audio circuitry. I circled the item numbers and they were a covey of .02 ufds.
::
::Starting with an .02 item / #42 coming off with the detected audio from the 75 and being fed into the high end of the volume control. Then the audio comes off from the wiper of the volume control and is fed thru .02 item / #43 , which feeds to the 1st grid(cap) of the 75. The amplified audio is taken off at the plate of the 75 and then feeds into the 1st grid of the #42 output tube thru .02 item / #59.
::Where is the .01 ufd ???
::Referencing your voltages given, the voltages fall within reason on the 75, with the exception that there must be an error in data gathering, as the two diode plates are connected together on pins 3 & 4 , yet you show an outrageously high voltage on one diode detector plate….in error assuredly.
:: Now, in referencing the marked up schema, and looking at the B+ flow of the dotted red lines coming up from the power supply up to feed the #42, there is an initial passage thru the field coil of the speaker and then the point where the reduced B+ feed out of the field coil branches out and is fed up to the screen grid of the 42, the B+ supply side of the output transformer and downwards thru the dotted orange supply line to feed the balance of the set AND the 75’s audio plate supply.
:: Your figures establish that voltage as being 129VDC ( assuredly being pulled down by heavy loading) with the # 42's plate voltage being circa zilch. So probably what has happened was that the set has defective / shorted item # 61 .02 capacitor , and you have somehow ended up with the tone control / switch being in that third position and the # 42 plate is being shorted to ground thru that capacitor.
::
::Normally, the first tone position has no effect, the second position shunts capacitor Item # 46 to effect a tonal change by shorting that .02 capacitor of a series RC network with its associated resistor item # 45. Those two RC components are the constituents of a loudness compensation circuit that is tied into that 225,000 k tap that you see on the lower portion of the volume control.
::At the lower positions of the volume control, it enhances the human ears perceived bass response at low volume levels, by slight treble attenuation , up to the threshold where the wiper passes onto that tap point. Or when you flip that tone adjustment to the mid position, and alter the tonal response in that manner.
::The third position of the tone control is where item # 61 / .02 ufd cap bypasses high audio frequencies on the plate circuit to ground. The third being the position of the most treble attenuation…..ergo….. most perceived bass enhancement..
::
::Considering yourself to find that unit to be shorted , its replacement with a disc ceramic unit of .02 ufd @ 1KV + voltage rating should probably give a reliability half life of a millennium.
::
::Tech Referencing Markup Schema:
::
::
::
::
::
::73's de Edd
::
::
::
::
::
::::Lewis:
::::
::::Disconnect what, where do I start, But could it not be the tone control in that it all relates to the circuit? Should I not disconnect or repair the tone control first and see what happens? Norm, what's your thoughts? Can I replace the 103K cap with a high value or not?
:::
:::Dave:
:::The cap in the tone control circuit must be replaced by the same value, but doesn't have to be in the circuit for the radio to work. It simply bypasses some of the high audio frequencies to ground for more bass in the output. Clip one lead of it for now and replace it when you don't have more important things to worry about.
:::Lewis
Oh-Tay….looks like you has done went and been sendicated..... two single section…. blue…Cornell Doubleflyer…. Electrolytic units to replace the old generation dual section electrolytic (# 67), and yes, the 16 ufd unit is to replace the item # 52 electrolytic. (Positive polarity is at the top of the schematics connections shown.)
The two 015 “mystery capacitors” mentioned are located down near the ac line input on the schematic and are in series across the AC line. They are the modern generation type of safety capacitors to be used in critical applications , like those line filter bypass functions .
That should be all.. will mark up anther troubleshooting schematic…. if deemed necessary…. Didn’t realize that you did not have the caps already replaced…that probably will take care if many of your units squirrelly quirks…beeps-squeaks-chirps.
73's de Edd
:Edd:
:
:Had a chance to look the schematic over and provide the following information. The .01 Cap is inside part 60, the Tone Control. This cap does not seem to be listed in the parts section or show in the schematic. It was a Spargue cap that seems to have been replaced at some point in the radios history. I replaced it with a .01 cap or a 103K and the control seems to work OK. The other cap, the 30-4017 a .1 cap or 104K was also replaced today and the radio is still OK, but it seems to take about 2 or more minutes to really warm up and become stable.
:
:As mentioned previously, part 67 cap, a 8-8 mfd unit was replaced with a Connell 10-10 cap, the cap having two leads coming off it. As part of a cap kit I purchased for the radio I have two blue 10 ufd caps which are probably to replace this cap, is this correct? Further, I have a single blue 16 uf cap which is probably to replace the part 52, the 16 mfd cap? I also have two square orange colored MKT .015K caps, Edd where do they go, I have no idea, and why are they so different than the rest.
:
:Im' sorry my friend for asking so many questions, but you are a tremendous help. Again thank you for your time and patience.
:
:
:
:
:
::Edd
::
::Thank you for getting back, your information and schematic, there fantastic. For now on I will identify myself as Dave B. It will take me a while to digest the information so I will advise. But, PTL the radio is working again it seems to have been the tone control. But two of the three positions produce a squeal along with it, the other one position is good and quiet I have one more capacitor to replace the 30-4017 cap, a .1 or 104K I can not find a 30-4017 list in the parts section but it's the capacitor that is in place.
::
::Edd, can you think of a single book that might really help a novice like me understand how to diagnose and repair these radios? Everything is new to me and I have a few radios I would really like to repair. Again, thank you Edd you are a tremendous help and a blessing.
::
::Yours humbly
::
::Dave B, or Preacher Dave
:::
:::
:::
:::
:::Dave …Dave …which Dave….’ya gotta have a program to identify the Dave…but possibly, this is Preacher Dave
:::
:::Looking at the thumbnail provided of the 620 I was hard pressed to find any .01’s in the audio circuitry. I circled the item numbers and they were a covey of .02 ufds.
:::
:::Starting with an .02 item / #42 coming off with the detected audio from the 75 and being fed into the high end of the volume control. Then the audio comes off from the wiper of the volume control and is fed thru .02 item / #43 , which feeds to the 1st grid(cap) of the 75. The amplified audio is taken off at the plate of the 75 and then feeds into the 1st grid of the #42 output tube thru .02 item / #59.
:::Where is the .01 ufd ???
:::Referencing your voltages given, the voltages fall within reason on the 75, with the exception that there must be an error in data gathering, as the two diode plates are connected together on pins 3 & 4 , yet you show an outrageously high voltage on one diode detector plate….in error assuredly.
::: Now, in referencing the marked up schema, and looking at the B+ flow of the dotted red lines coming up from the power supply up to feed the #42, there is an initial passage thru the field coil of the speaker and then the point where the reduced B+ feed out of the field coil branches out and is fed up to the screen grid of the 42, the B+ supply side of the output transformer and downwards thru the dotted orange supply line to feed the balance of the set AND the 75’s audio plate supply.
::: Your figures establish that voltage as being 129VDC ( assuredly being pulled down by heavy loading) with the # 42's plate voltage being circa zilch. So probably what has happened was that the set has defective / shorted item # 61 .02 capacitor , and you have somehow ended up with the tone control / switch being in that third position and the # 42 plate is being shorted to ground thru that capacitor.
:::
:::Normally, the first tone position has no effect, the second position shunts capacitor Item # 46 to effect a tonal change by shorting that .02 capacitor of a series RC network with its associated resistor item # 45. Those two RC components are the constituents of a loudness compensation circuit that is tied into that 225,000 k tap that you see on the lower portion of the volume control.
:::At the lower positions of the volume control, it enhances the human ears perceived bass response at low volume levels, by slight treble attenuation , up to the threshold where the wiper passes onto that tap point. Or when you flip that tone adjustment to the mid position, and alter the tonal response in that manner.
:::The third position of the tone control is where item # 61 / .02 ufd cap bypasses high audio frequencies on the plate circuit to ground. The third being the position of the most treble attenuation…..ergo….. most perceived bass enhancement..
:::
:::Considering yourself to find that unit to be shorted , its replacement with a disc ceramic unit of .02 ufd @ 1KV + voltage rating should probably give a reliability half life of a millennium.
:::
:::Tech Referencing Markup Schema:
:::
:::
:::
:::
:::
:::73's de Edd
:::
:::
:::
:::
:::
:::::Lewis:
:::::
:::::Disconnect what, where do I start, But could it not be the tone control in that it all relates to the circuit? Should I not disconnect or repair the tone control first and see what happens? Norm, what's your thoughts? Can I replace the 103K cap with a high value or not?
::::
::::Dave:
::::The cap in the tone control circuit must be replaced by the same value, but doesn't have to be in the circuit for the radio to work. It simply bypasses some of the high audio frequencies to ground for more bass in the output. Clip one lead of it for now and replace it when you don't have more important things to worry about.
::::Lewis
Again thank you, two qyestions perhaps
1. A good overall book teach me about old radio and that will give me some insight on how to trouble shoot and repair these radios? I have other radios and want to restore them as well.
2. Obtained a working SG 85C/URM 25D signal generator, I think I can set it up but really don't know how to tune a radio with it. I know it generates a signal into the radio but how does one know when the best range has been obtained other than be lisitng for the strongest signal?
It seems from your knowledge of these radios that you have been around this business for quite awhile and know a great deal.
:SRC=http://img411.imageshack.us/img411/2761/fenceeyeslinewidthgauk8.gif>
:
:
:Oh-Tay….looks like you has done went and been sendicated..... two single section…. blue…Cornell Doubleflyer…. Electrolytic units to replace the old generation dual section electrolytic (# 67), and yes, the 16 ufd unit is to replace the item # 52 electrolytic. (Positive polarity is at the top of the schematics connections shown.)
:
:
:The two 015 “mystery capacitors” mentioned are located down near the ac line input on the schematic and are in series across the AC line. They are the modern generation type of safety capacitors to be used in critical applications , like those line filter bypass functions .
:
:That should be all.. will mark up anther troubleshooting schematic…. if deemed necessary…. Didn’t realize that you did not have the caps already replaced…that probably will take care if many of your units squirrelly quirks…beeps-squeaks-chirps.
:
:
:
:73's de Edd
:
:
:
:
:
:
:
:
:
:
::Edd:
::
::Had a chance to look the schematic over and provide the following information. The .01 Cap is inside part 60, the Tone Control. This cap does not seem to be listed in the parts section or show in the schematic. It was a Spargue cap that seems to have been replaced at some point in the radios history. I replaced it with a .01 cap or a 103K and the control seems to work OK. The other cap, the 30-4017 a .1 cap or 104K was also replaced today and the radio is still OK, but it seems to take about 2 or more minutes to really warm up and become stable.
::
::As mentioned previously, part 67 cap, a 8-8 mfd unit was replaced with a Connell 10-10 cap, the cap having two leads coming off it. As part of a cap kit I purchased for the radio I have two blue 10 ufd caps which are probably to replace this cap, is this correct? Further, I have a single blue 16 uf cap which is probably to replace the part 52, the 16 mfd cap? I also have two square orange colored MKT .015K caps, Edd where do they go, I have no idea, and why are they so different than the rest.
::
::Im' sorry my friend for asking so many questions, but you are a tremendous help. Again thank you for your time and patience.
::
::
::
::
::
:::Edd
:::
:::Thank you for getting back, your information and schematic, there fantastic. For now on I will identify myself as Dave B. It will take me a while to digest the information so I will advise. But, PTL the radio is working again it seems to have been the tone control. But two of the three positions produce a squeal along with it, the other one position is good and quiet I have one more capacitor to replace the 30-4017 cap, a .1 or 104K I can not find a 30-4017 list in the parts section but it's the capacitor that is in place.
:::
:::Edd, can you think of a single book that might really help a novice like me understand how to diagnose and repair these radios? Everything is new to me and I have a few radios I would really like to repair. Again, thank you Edd you are a tremendous help and a blessing.
:::
:::Yours humbly
:::
:::Dave B, or Preacher Dave
::::
::::
::::
::::
::::Dave …Dave …which Dave….’ya gotta have a program to identify the Dave…but possibly, this is Preacher Dave
::::
::::Looking at the thumbnail provided of the 620 I was hard pressed to find any .01’s in the audio circuitry. I circled the item numbers and they were a covey of .02 ufds.
::::
::::Starting with an .02 item / #42 coming off with the detected audio from the 75 and being fed into the high end of the volume control. Then the audio comes off from the wiper of the volume control and is fed thru .02 item / #43 , which feeds to the 1st grid(cap) of the 75. The amplified audio is taken off at the plate of the 75 and then feeds into the 1st grid of the #42 output tube thru .02 item / #59.
::::Where is the .01 ufd ???
::::Referencing your voltages given, the voltages fall within reason on the 75, with the exception that there must be an error in data gathering, as the two diode plates are connected together on pins 3 & 4 , yet you show an outrageously high voltage on one diode detector plate….in error assuredly.
:::: Now, in referencing the marked up schema, and looking at the B+ flow of the dotted red lines coming up from the power supply up to feed the #42, there is an initial passage thru the field coil of the speaker and then the point where the reduced B+ feed out of the field coil branches out and is fed up to the screen grid of the 42, the B+ supply side of the output transformer and downwards thru the dotted orange supply line to feed the balance of the set AND the 75’s audio plate supply.
:::: Your figures establish that voltage as being 129VDC ( assuredly being pulled down by heavy loading) with the # 42's plate voltage being circa zilch. So probably what has happened was that the set has defective / shorted item # 61 .02 capacitor , and you have somehow ended up with the tone control / switch being in that third position and the # 42 plate is being shorted to ground thru that capacitor.
::::
::::Normally, the first tone position has no effect, the second position shunts capacitor Item # 46 to effect a tonal change by shorting that .02 capacitor of a series RC network with its associated resistor item # 45. Those two RC components are the constituents of a loudness compensation circuit that is tied into that 225,000 k tap that you see on the lower portion of the volume control.
::::At the lower positions of the volume control, it enhances the human ears perceived bass response at low volume levels, by slight treble attenuation , up to the threshold where the wiper passes onto that tap point. Or when you flip that tone adjustment to the mid position, and alter the tonal response in that manner.
::::The third position of the tone control is where item # 61 / .02 ufd cap bypasses high audio frequencies on the plate circuit to ground. The third being the position of the most treble attenuation…..ergo….. most perceived bass enhancement..
::::
::::Considering yourself to find that unit to be shorted , its replacement with a disc ceramic unit of .02 ufd @ 1KV + voltage rating should probably give a reliability half life of a millennium.
::::
::::Tech Referencing Markup Schema:
::::
::::
::::
::::
::::
::::73's de Edd
::::
::::
::::
::::
::::
::::::Lewis:
::::::
::::::Disconnect what, where do I start, But could it not be the tone control in that it all relates to the circuit? Should I not disconnect or repair the tone control first and see what happens? Norm, what's your thoughts? Can I replace the 103K cap with a high value or not?
:::::
:::::Dave:
:::::The cap in the tone control circuit must be replaced by the same value, but doesn't have to be in the circuit for the radio to work. It simply bypasses some of the high audio frequencies to ground for more bass in the output. Clip one lead of it for now and replace it when you don't have more important things to worry about.
:::::Lewis
:
:Again thank you, two qyestions perhaps
:
:1. A good overall book teach me about old radio and that will give me some insight on how to trouble shoot and repair these radios? I have other radios and want to restore them as well.
:2. Obtained a working SG 85C/URM 25D signal generator, I think I can set it up but really don't know how to tune a radio with it. I know it generates a signal into the radio but how does one know when the best range has been obtained other than be lisitng for the strongest signal?
:
:It seems from your knowledge of these radios that you have been around this business for quite awhile and know a great deal.
Dave:
Go to this site:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
http://funwithtubes.com/
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
and study the AA5 part, it will tell you just about all there is to know about the AC/DC radio, as they were known then. Then you will have to gain experience by trial and error (and asking us). Things will start falling in place, and one day you will think you have it knocked, then something will come along to embarass you. Don't be ashamed, it has happened to all of us.
Lewis
Great advise, will do, your right, I have to put the time in and pay the price. I will try the sight. Thanks
Dave
::Edd:
::
::Again thank you, two qyestions perhaps
::
::1. A good overall book teach me about old radio and that will give me some insight on how to trouble shoot and repair these radios? I have other radios and want to restore them as well.
::2. Obtained a working SG 85C/URM 25D signal generator, I think I can set it up but really don't know how to tune a radio with it. I know it generates a signal into the radio but how does one know when the best range has been obtained other than be lisitng for the strongest signal?
::
::It seems from your knowledge of these radios that you have been around this business for quite awhile and know a great deal.
:
:Dave:
:Go to this site:
:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:http://funwithtubes.com/
:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:
:and study the AA5 part, it will tell you just about all there is to know about the AC/DC radio, as they were known then. Then you will have to gain experience by trial and error (and asking us). Things will start falling in place, and one day you will think you have it knocked, then something will come along to embarass you. Don't be ashamed, it has happened to all of us.
:
:Lewis
: