Zenith 4-v-31 sort of

9/20/2004 11:01:02 PMThomas Dermody

What article did I write? Can't find one on 8-15 that is all that interesting....just some replies and stuff.

The coil you bought from AES probably is slug tuned, if you bought their universal oscillator coil. What is the original model number of your radio that you are converting to AC? Why, as you convert it to AC, did you need to re-do all of the circuitry? Why not either build a simple 117Z6 power supply with appropriate ballasts for the tube filaments (leaving in the battery tubes), or if tube substitutions must be made, and the radio is converted to AC complete with transformer, why must the circuits be modified extensively?

If you have a new oscillator coil, and you're picking up short wave, then you have to go to Radio Shack and get their plastic alignment tool kit. Then figure out what the radio was originally designed to be tuned to. The IF transformers must be tuned properly first, and then the oscillator coil must be tuned to its proper frequency. This is done with the slug in the middle. Depending on the circuitry, a frequency may be chosen towards the middle of the dial, or the end, and then a padder condenser is used to adjust the other end of the dial. If your radio has only a trimmer on the tuning condenser, then you may want to adjust the slug until broadcast is received and somewhat in alignment, and then use the trimmer to synchronize the top end of the dial, and then go back and synchronize the bottom end of the dial with the slug. This process may have to be repeated several times. Depending on how well the tuning condenser matches up with the oscillator coil, you may have a little trouble. You may even have to change other components in the radio.

What was wrong with the original oscillator coil? If you must use the 3 lug universal coil, connect the long half of the center tap to pin 5 of the 6A7 tube through a .0001 mfd condenser. Connect a 22k resistor from pin 5 to pin 6. Connect the center tap to pin 6. connect the short half of the coil to B-. Connect pin 4 to pin 3, and pin 3 to the RF screen grid supply. If this is the same as the B+ sent to the plates, then this is where it is connected. Usually the screen grids are fed through a resistor in AC radios. You are better off using the 6SA7G tube in place of the 6A7 tube, as it is appropriately designed for 3 lug oscillator coils. The 6A7 tube is designed for oscillator coils that have two definite separate coils. The large coil is used in the grid circuit, and the small coil is used in the plate circuit (grid 2 of the 6A7 tube).
Thomas

:Hi again
:I am still working on the converted Zenith 4-v-31. It is a battery radio converted to 110v. I have everything just about right except for the oscillator circuit. The coil that was with the original radio seems to be actually two coils, one with a center tap. I bought a coil from AES, but it was certainly wasn't right, because, I turned the radio into SW! And it is not a SW radio. I am using a 6A7 tube for the osc/1st detector curcuit, but the schematic that I am using doesn't show me where or how the osc coil is hooked up in the circuit. I read with interst Mr Dermody's article posted 08/15, but would like a little more help. I am thinking about using a 5 tube schematic from Zenith and trying that, but it still doesn't show how to wire up the oscillator coil. Any help would be appreciated. Thanks

9/21/2004 12:48:42 AMJohn D. Weeks

:What article did I write? Can't find one on 8-15 that is all that interesting....just some replies and stuff.
:
:The coil you bought from AES probably is slug tuned, if you bought their universal oscillator coil. What is the original model number of your radio that you are converting to AC? Why, as you convert it to AC, did you need to re-do all of the circuitry? Why not either build a simple 117Z6 power supply with appropriate ballasts for the tube filaments (leaving in the battery tubes), or if tube substitutions must be made, and the radio is converted to AC complete with transformer, why must the circuits be modified extensively?
:
:If you have a new oscillator coil, and you're picking up short wave, then you have to go to Radio Shack and get their plastic alignment tool kit. Then figure out what the radio was originally designed to be tuned to. The IF transformers must be tuned properly first, and then the oscillator coil must be tuned to its proper frequency. This is done with the slug in the middle. Depending on the circuitry, a frequency may be chosen towards the middle of the dial, or the end, and then a padder condenser is used to adjust the other end of the dial. If your radio has only a trimmer on the tuning condenser, then you may want to adjust the slug until broadcast is received and somewhat in alignment, and then use the trimmer to synchronize the top end of the dial, and then go back and synchronize the bottom end of the dial with the slug. This process may have to be repeated several times. Depending on how well the tuning condenser matches up with the oscillator coil, you may have a little trouble. You may even have to change other components in the radio.
:
:What was wrong with the original oscillator coil? If you must use the 3 lug universal coil, connect the long half of the center tap to pin 5 of the 6A7 tube through a .0001 mfd condenser. Connect a 22k resistor from pin 5 to pin 6. Connect the center tap to pin 6. connect the short half of the coil to B-. Connect pin 4 to pin 3, and pin 3 to the RF screen grid supply. If this is the same as the B+ sent to the plates, then this is where it is connected. Usually the screen grids are fed through a resistor in AC radios. You are better off using the 6SA7G tube in place of the 6A7 tube, as it is appropriately designed for 3 lug oscillator coils. The 6A7 tube is designed for oscillator coils that have two definite separate coils. The large coil is used in the grid circuit, and the small coil is used in the plate circuit (grid 2 of the 6A7 tube).
:Thomas
:
::Hi again
::I am still working on the converted Zenith 4-v-31. It is a battery radio converted to 110v. I have everything just about right except for the oscillator circuit. The coil that was with the original radio seems to be actually two coils, one with a center tap. I bought a coil from AES, but it was certainly wasn't right, because, I turned the radio into SW! And it is not a SW radio. I am using a 6A7 tube for the osc/1st detector curcuit, but the schematic that I am using doesn't show me where or how the osc coil is hooked up in the circuit. I read with interst Mr Dermody's article posted 08/15, but would like a little more help. I am thinking about using a 5 tube schematic from Zenith and trying that, but it still doesn't show how to wire up the oscillator coil. Any help would be appreciated. Thanks

The radio was converted to 110 before I got it. (my grandmother's). The tech that did it did not leave a schematic and the work he performed did not match up on the schematic, (changed tubes, resistors,etc). The osc I bought does not have a slug. The original osc coil has four lugs, plus what looks like a center tap loose ( I used an ohm meter). I will see if AES has the 6SA7G that you recommend. Thanks

9/21/2004 12:50:04 AMJohn Weeks

::What article did I write? Can't find one on 8-15 that is all that interesting....just some replies and stuff.
::
::The coil you bought from AES probably is slug tuned, if you bought their universal oscillator coil. What is the original model number of your radio that you are converting to AC? Why, as you convert it to AC, did you need to re-do all of the circuitry? Why not either build a simple 117Z6 power supply with appropriate ballasts for the tube filaments (leaving in the battery tubes), or if tube substitutions must be made, and the radio is converted to AC complete with transformer, why must the circuits be modified extensively?
::
::If you have a new oscillator coil, and you're picking up short wave, then you have to go to Radio Shack and get their plastic alignment tool kit. Then figure out what the radio was originally designed to be tuned to. The IF transformers must be tuned properly first, and then the oscillator coil must be tuned to its proper frequency. This is done with the slug in the middle. Depending on the circuitry, a frequency may be chosen towards the middle of the dial, or the end, and then a padder condenser is used to adjust the other end of the dial. If your radio has only a trimmer on the tuning condenser, then you may want to adjust the slug until broadcast is received and somewhat in alignment, and then use the trimmer to synchronize the top end of the dial, and then go back and synchronize the bottom end of the dial with the slug. This process may have to be repeated several times. Depending on how well the tuning condenser matches up with the oscillator coil, you may have a little trouble. You may even have to change other components in the radio.
::
::What was wrong with the original oscillator coil? If you must use the 3 lug universal coil, connect the long half of the center tap to pin 5 of the 6A7 tube through a .0001 mfd condenser. Connect a 22k resistor from pin 5 to pin 6. Connect the center tap to pin 6. connect the short half of the coil to B-. Connect pin 4 to pin 3, and pin 3 to the RF screen grid supply. If this is the same as the B+ sent to the plates, then this is where it is connected. Usually the screen grids are fed through a resistor in AC radios. You are better off using the 6SA7G tube in place of the 6A7 tube, as it is appropriately designed for 3 lug oscillator coils. The 6A7 tube is designed for oscillator coils that have two definite separate coils. The large coil is used in the grid circuit, and the small coil is used in the plate circuit (grid 2 of the 6A7 tube).
::Thomas
::
:::Hi again
:::I am still working on the converted Zenith 4-v-31. It is a battery radio converted to 110v. I have everything just about right except for the oscillator circuit. The coil that was with the original radio seems to be actually two coils, one with a center tap. I bought a coil from AES, but it was certainly wasn't right, because, I turned the radio into SW! And it is not a SW radio. I am using a 6A7 tube for the osc/1st detector curcuit, but the schematic that I am using doesn't show me where or how the osc coil is hooked up in the circuit. I read with interst Mr Dermody's article posted 08/15, but would like a little more help. I am thinking about using a 5 tube schematic from Zenith and trying that, but it still doesn't show how to wire up the oscillator coil. Any help would be appreciated. Thanks
:
:The radio was converted to 110 before I got it. (my grandmother's). The tech that did it did not leave a schematic and the work he performed did not match up on the schematic, (changed tubes, resistors,etc). The osc I bought does not have a slug. The original osc coil has four lugs, plus what looks like a center tap loose ( I used an ohm meter). I will see if AES has the 6SA7G that you recommend. Thanks

Zenith 4-V-31 6 volt farm radio 1936

9/21/2004 8:39:16 AMThomas Dermody

ah........it's a 6 volt farm radio. didn't know that. Still, why must the oscillator coil be replaced?

9/21/2004 8:53:33 AMThomas Dermody

That radio originally had #15 tubes for both the oscillator and IF. The filaments were strung in series with a resistor to equal 6 volts. I do not see at all why the entire radio wouldn't work as is on 6 volts AC. If all of the original components remain, convert the radio back to the #15 tubes as wired originally. That way you can make use of the original oscillator coil that was designed to work with all of the other components (tuning condenser, etc.).

If you have it wired for the 6A7, how is that new oscillator coil wired to the tube?

Thomas

:ah........it's a 6 volt farm radio. didn't know that. Still, why must the oscillator coil be replaced?

9/21/2004 8:37:15 AMThomas Dermody

Well, don't go changing tubes yet. What was wrong with the original oscillator coil? If there's nothing wrong with it, it'll work very well with the 6A7 tube. The only reason to change tubes is if you use a 3 lug oscillator coil. 6A7 and 6A8 are designed for the 4 lug 2 coil oscillator coil, and 6SA7 is designed for the 3 lug oscillator coil that is one coil with a center tap. The former coil usually has one section hooked to the plate circuit and one to the grid circuit. The latter coil is hooked to the grid and cathode circuit, and so it does not need to be two separate coils. The tap on your original coil may have been for short wave or something. There should be a small coil (low resistance). This is the plate coil. Then there should be a larger coil (higher resistance and more turns of wire). This is the grid coil. The tap should be on this second coil. By shortening the coil, you raise the frequency at which it operates. Using the whole coil will likely operate at broadcast frequencies. Selecting only part of the coil through this tap will give you short wave frequencies of some sort. I'd like to know what kind of circuit you have going on first, and why you feel it necessary to replace the original coil.

Thomas

9/21/2004 3:17:58 PMJohn D. Weeks

:Well, don't go changing tubes yet. What was wrong with the original oscillator coil? If there's nothing wrong with it, it'll work very well with the 6A7 tube. The only reason to change tubes is if you use a 3 lug oscillator coil. 6A7 and 6A8 are designed for the 4 lug 2 coil oscillator coil, and 6SA7 is designed for the 3 lug oscillator coil that is one coil with a center tap. The former coil usually has one section hooked to the plate circuit and one to the grid circuit. The latter coil is hooked to the grid and cathode circuit, and so it does not need to be two separate coils. The tap on your original coil may have been for short wave or something. There should be a small coil (low resistance). This is the plate coil. Then there should be a larger coil (higher resistance and more turns of wire). This is the grid coil. The tap should be on this second coil. By shortening the coil, you raise the frequency at which it operates. Using the whole coil will likely operate at broadcast frequencies. Selecting only part of the coil through this tap will give you short wave frequencies of some sort. I'd like to know what kind of circuit you have going on first, and why you feel it necessary to replace the original coil.
:
:Thomas
:
:::What article did I write? Can't find one on 8-15 that is all that interesting....just some replies and stuff.
:::
:::The coil you bought from AES probably is slug tuned, if you bought their universal oscillator coil. What is the original model number of your radio that you are converting to AC? Why, as you convert it to AC, did you need to re-do all of the circuitry? Why not either build a simple 117Z6 power supply with appropriate ballasts for the tube filaments (leaving in the battery tubes), or if tube substitutions must be made, and the radio is converted to AC complete with transformer, why must the circuits be modified extensively?
:::
:::If you have a new oscillator coil, and you're picking up short wave, then you have to go to Radio Shack and get their plastic alignment tool kit. Then figure out what the radio was originally designed to be tuned to. The IF transformers must be tuned properly first, and then the oscillator coil must be tuned to its proper frequency. This is done with the slug in the middle. Depending on the circuitry, a frequency may be chosen towards the middle of the dial, or the end, and then a padder condenser is used to adjust the other end of the dial. If your radio has only a trimmer on the tuning condenser, then you may want to adjust the slug until broadcast is received and somewhat in alignment, and then use the trimmer to synchronize the top end of the dial, and then go back and synchronize the bottom end of the dial with the slug. This process may have to be repeated several times. Depending on how well the tuning condenser matches up with the oscillator coil, you may have a little trouble. You may even have to change other components in the radio.
:::
:::What was wrong with the original oscillator coil? If you must use the 3 lug universal coil, connect the long half of the center tap to pin 5 of the 6A7 tube through a .0001 mfd condenser. Connect a 22k resistor from pin 5 to pin 6. Connect the center tap to pin 6. connect the short half of the coil to B-. Connect pin 4 to pin 3, and pin 3 to the RF screen grid supply. If this is the same as the B+ sent to the plates, then this is where it is connected. Usually the screen grids are fed through a resistor in AC radios. You are better off using the 6SA7G tube in place of the 6A7 tube, as it is appropriately designed for 3 lug oscillator coils. The 6A7 tube is designed for oscillator coils that have two definite separate coils. The large coil is used in the grid circuit, and the small coil is used in the plate circuit (grid 2 of the 6A7 tube).
:::Thomas
:::
::::Hi again
::::I am still working on the converted Zenith 4-v-31. It is a battery radio converted to 110v. I have everything just about right except for the oscillator circuit. The coil that was with the original radio seems to be actually two coils, one with a center tap. I bought a coil from AES, but it was certainly wasn't right, because, I turned the radio into SW! And it is not a SW radio. I am using a 6A7 tube for the osc/1st detector curcuit, but the schematic that I am using doesn't show me where or how the osc coil is hooked up in the circuit. I read with interst Mr Dermody's article posted 08/15, but would like a little more help. I am thinking about using a 5 tube schematic from Zenith and trying that, but it still doesn't show how to wire up the oscillator coil. Any help would be appreciated. Thanks
::You want the long version or short version? When I got the radio, it had been in storage for years. I could not read the number on the osc tube, but the socket had 6F7 on it. I run radio stations, and my engineer thought that the 6F7 was the right tube. When I put it in, of course, it didn't work. He suggested that we re-wire the radio, as the rest of it was not close to the original schematic. Since then, I got the old tube and discovered that it was supposed to be a 6A7. I got the schematic from www.gbronline.com\radioguy\index.htm, using the troubleshooting a superhetrodyne reciever. It used a 6A8 for osc. I couldn't get the coil to work, so I bought a new osc. When hooked up, I got SW. (wrong Frequency). But, it worked really well with SW. I then hooked up part of the old osc with half of the new coil, and it worked for just one station, but would not sustain oscillation. If cans are tuned properly (456). Still using original variable condensor and IF cans and antenna can. Using 78 for IF, 75 first det, 42 power, and 80 rectifier. The tech that converted the radio to 110 did not use same resistors, caps, etc. So since I did not have a schematic work with, I went to one that seemed to be close. Thats my story and I'm sticking to it. (ha)
::The radio was converted to 110 before I got it. (my grandmother's). The tech that did it did not leave a schematic and the work he performed did not match up on the schematic, (changed tubes, resistors,etc). The osc I bought does not have a slug. The original osc coil has four lugs, plus what looks like a center tap loose ( I used an ohm meter). I will see if AES has the 6SA7G that you recommend. Thanks

9/21/2004 3:24:00 PMJohn Weeks

::Well, don't go changing tubes yet. What was wrong with the original oscillator coil? If there's nothing wrong with it, it'll work very well with the 6A7 tube. The only reason to change tubes is if you use a 3 lug oscillator coil. 6A7 and 6A8 are designed for the 4 lug 2 coil oscillator coil, and 6SA7 is designed for the 3 lug oscillator coil that is one coil with a center tap. The former coil usually has one section hooked to the plate circuit and one to the grid circuit. The latter coil is hooked to the grid and cathode circuit, and so it does not need to be two separate coils. The tap on your original coil may have been for short wave or something. There should be a small coil (low resistance). This is the plate coil. Then there should be a larger coil (higher resistance and more turns of wire). This is the grid coil. The tap should be on this second coil. By shortening the coil, you raise the frequency at which it operates. Using the whole coil will likely operate at broadcast frequencies. Selecting only part of the coil through this tap will give you short wave frequencies of some sort. I'd like to know what kind of circuit you have going on first, and why you feel it necessary to replace the original coil.
::
::Thomas
::
::::What article did I write? Can't find one on 8-15 that is all that interesting....just some replies and stuff.
::::
::::The coil you bought from AES probably is slug tuned, if you bought their universal oscillator coil. What is the original model number of your radio that you are converting to AC? Why, as you convert it to AC, did you need to re-do all of the circuitry? Why not either build a simple 117Z6 power supply with appropriate ballasts for the tube filaments (leaving in the battery tubes), or if tube substitutions must be made, and the radio is converted to AC complete with transformer, why must the circuits be modified extensively?
::::
::::If you have a new oscillator coil, and you're picking up short wave, then you have to go to Radio Shack and get their plastic alignment tool kit. Then figure out what the radio was originally designed to be tuned to. The IF transformers must be tuned properly first, and then the oscillator coil must be tuned to its proper frequency. This is done with the slug in the middle. Depending on the circuitry, a frequency may be chosen towards the middle of the dial, or the end, and then a padder condenser is used to adjust the other end of the dial. If your radio has only a trimmer on the tuning condenser, then you may want to adjust the slug until broadcast is received and somewhat in alignment, and then use the trimmer to synchronize the top end of the dial, and then go back and synchronize the bottom end of the dial with the slug. This process may have to be repeated several times. Depending on how well the tuning condenser matches up with the oscillator coil, you may have a little trouble. You may even have to change other components in the radio.
::::
::::What was wrong with the original oscillator coil? If you must use the 3 lug universal coil, connect the long half of the center tap to pin 5 of the 6A7 tube through a .0001 mfd condenser. Connect a 22k resistor from pin 5 to pin 6. Connect the center tap to pin 6. connect the short half of the coil to B-. Connect pin 4 to pin 3, and pin 3 to the RF screen grid supply. If this is the same as the B+ sent to the plates, then this is where it is connected. Usually the screen grids are fed through a resistor in AC radios. You are better off using the 6SA7G tube in place of the 6A7 tube, as it is appropriately designed for 3 lug oscillator coils. The 6A7 tube is designed for oscillator coils that have two definite separate coils. The large coil is used in the grid circuit, and the small coil is used in the plate circuit (grid 2 of the 6A7 tube).
::::Thomas
::::
:::::Hi again
:::::I am still working on the converted Zenith 4-v-31. It is a battery radio converted to 110v. I have everything just about right except for the oscillator circuit. The coil that was with the original radio seems to be actually two coils, one with a center tap. I bought a coil from AES, but it was certainly wasn't right, because, I turned the radio into SW! And it is not a SW radio. I am using a 6A7 tube for the osc/1st detector curcuit, but the schematic that I am using doesn't show me where or how the osc coil is hooked up in the circuit. I read with interst Mr Dermody's article posted 08/15, but would like a little more help. I am thinking about using a 5 tube schematic from Zenith and trying that, but it still doesn't show how to wire up the oscillator coil. Any help would be appreciated. Thanks
:::You want the long version or short version? When I got the radio, it had been in storage for years. I could not read the number on the osc tube, but the socket had 6F7 on it. I run radio stations, and my engineer thought that the 6F7 was the right tube. When I put it in, of course, it didn't work. He suggested that we re-wire the radio, as the rest of it was not close to the original schematic. Since then, I got the old tube and discovered that it was supposed to be a 6A7. I got the schematic from www.gbronline.com\radioguy\index.htm, using the troubleshooting a superhetrodyne reciever. It used a 6A8 for osc. I couldn't get the coil to work, so I bought a new osc. When hooked up, I got SW. (wrong Frequency). But, it worked really well with SW. I then hooked up part of the old osc with half of the new coil, and it worked for just one station, but would not sustain oscillation. If cans are tuned properly (456). Still using original variable condensor and IF cans and antenna can. Using 78 for IF, 75 first det, 42 power, and 80 rectifier. The tech that converted the radio to 110 did not use same resistors, caps, etc. So since I did not have a schematic work with, I went to one that seemed to be close. Thats my story and I'm sticking to it. (ha)
:::The radio was converted to 110 before I got it. (my grandmother's). The tech that did it did not leave a schematic and the work he performed did not match up on the schematic, (changed tubes, resistors,etc). The osc I bought does not have a slug. The original osc coil has four lugs, plus what looks like a center tap loose ( I used an ohm meter). I will see if AES has the 6SA7G that you recommend. Thanks
By the way, it was a response to RCA AM band gone haywire, on 8\15. And, it was good.

9/21/2004 6:08:36 PMJohn D. Weeks

:::Well, don't go changing tubes yet. What was wrong with the original oscillator coil? If there's nothing wrong with it, it'll work very well with the 6A7 tube. The only reason to change tubes is if you use a 3 lug oscillator coil. 6A7 and 6A8 are designed for the 4 lug 2 coil oscillator coil, and 6SA7 is designed for the 3 lug oscillator coil that is one coil with a center tap. The former coil usually has one section hooked to the plate circuit and one to the grid circuit. The latter coil is hooked to the grid and cathode circuit, and so it does not need to be two separate coils. The tap on your original coil may have been for short wave or something. There should be a small coil (low resistance). This is the plate coil. Then there should be a larger coil (higher resistance and more turns of wire). This is the grid coil. The tap should be on this second coil. By shortening the coil, you raise the frequency at which it operates. Using the whole coil will likely operate at broadcast frequencies. Selecting only part of the coil through this tap will give you short wave frequencies of some sort. I'd like to know what kind of circuit you have going on first, and why you feel it necessary to replace the original coil.
:::
:::Thomas
:::
:::::What article did I write? Can't find one on 8-15 that is all that interesting....just some replies and stuff.
:::::
:::::The coil you bought from AES probably is slug tuned, if you bought their universal oscillator coil. What is the original model number of your radio that you are converting to AC? Why, as you convert it to AC, did you need to re-do all of the circuitry? Why not either build a simple 117Z6 power supply with appropriate ballasts for the tube filaments (leaving in the battery tubes), or if tube substitutions must be made, and the radio is converted to AC complete with transformer, why must the circuits be modified extensively?
:::::
:::::If you have a new oscillator coil, and you're picking up short wave, then you have to go to Radio Shack and get their plastic alignment tool kit. Then figure out what the radio was originally designed to be tuned to. The IF transformers must be tuned properly first, and then the oscillator coil must be tuned to its proper frequency. This is done with the slug in the middle. Depending on the circuitry, a frequency may be chosen towards the middle of the dial, or the end, and then a padder condenser is used to adjust the other end of the dial. If your radio has only a trimmer on the tuning condenser, then you may want to adjust the slug until broadcast is received and somewhat in alignment, and then use the trimmer to synchronize the top end of the dial, and then go back and synchronize the bottom end of the dial with the slug. This process may have to be repeated several times. Depending on how well the tuning condenser matches up with the oscillator coil, you may have a little trouble. You may even have to change other components in the radio.
:::::
:::::What was wrong with the original oscillator coil? If you must use the 3 lug universal coil, connect the long half of the center tap to pin 5 of the 6A7 tube through a .0001 mfd condenser. Connect a 22k resistor from pin 5 to pin 6. Connect the center tap to pin 6. connect the short half of the coil to B-. Connect pin 4 to pin 3, and pin 3 to the RF screen grid supply. If this is the same as the B+ sent to the plates, then this is where it is connected. Usually the screen grids are fed through a resistor in AC radios. You are better off using the 6SA7G tube in place of the 6A7 tube, as it is appropriately designed for 3 lug oscillator coils. The 6A7 tube is designed for oscillator coils that have two definite separate coils. The large coil is used in the grid circuit, and the small coil is used in the plate circuit (grid 2 of the 6A7 tube).
:::::Thomas
:::::
::::::Hi again
::::::I am still working on the converted Zenith 4-v-31. It is a battery radio converted to 110v. I have everything just about right except for the oscillator circuit. The coil that was with the original radio seems to be actually two coils, one with a center tap. I bought a coil from AES, but it was certainly wasn't right, because, I turned the radio into SW! And it is not a SW radio. I am using a 6A7 tube for the osc/1st detector curcuit, but the schematic that I am using doesn't show me where or how the osc coil is hooked up in the circuit. I read with interst Mr Dermody's article posted 08/15, but would like a little more help. I am thinking about using a 5 tube schematic from Zenith and trying that, but it still doesn't show how to wire up the oscillator coil. Any help would be appreciated. Thanks
::::You want the long version or short version? When I got the radio, it had been in storage for years. I could not read the number on the osc tube, but the socket had 6F7 on it. I run radio stations, and my engineer thought that the 6F7 was the right tube. When I put it in, of course, it didn't work. He suggested that we re-wire the radio, as the rest of it was not close to the original schematic. Since then, I got the old tube and discovered that it was supposed to be a 6A7. I got the schematic from www.gbronline.com\radioguy\index.htm, using the troubleshooting a superhetrodyne reciever. It used a 6A8 for osc. I couldn't get the coil to work, so I bought a new osc. When hooked up, I got SW. (wrong Frequency). But, it worked really well with SW. I then hooked up part of the old osc with half of the new coil, and it worked for just one station, but would not sustain oscillation. If cans are tuned properly (456). Still using original variable condensor and IF cans and antenna can. Using 78 for IF, 75 first det, 42 power, and 80 rectifier. The tech that converted the radio to 110 did not use same resistors, caps, etc. So since I did not have a schematic work with, I went to one that seemed to be close. Thats my story and I'm sticking to it. (ha)
::::The radio was converted to 110 before I got it. (my grandmother's). The tech that did it did not leave a schematic and the work he performed did not match up on the schematic, (changed tubes, resistors,etc). The osc I bought does not have a slug. The original osc coil has four lugs, plus what looks like a center tap loose ( I used an ohm meter). I will see if AES has the 6SA7G that you recommend. Thanks
:By the way, it was a response to RCA AM band gone haywire, on 8\15. And, it was good.

9/21/2004 6:12:25 PMJohn D. Weeks

::::Well, don't go changing tubes yet. What was wrong with the original oscillator coil? If there's nothing wrong with it, it'll work very well with the 6A7 tube. The only reason to change tubes is if you use a 3 lug oscillator coil. 6A7 and 6A8 are designed for the 4 lug 2 coil oscillator coil, and 6SA7 is designed for the 3 lug oscillator coil that is one coil with a center tap. The former coil usually has one section hooked to the plate circuit and one to the grid circuit. The latter coil is hooked to the grid and cathode circuit, and so it does not need to be two separate coils. The tap on your original coil may have been for short wave or something. There should be a small coil (low resistance). This is the plate coil. Then there should be a larger coil (higher resistance and more turns of wire). This is the grid coil. The tap should be on this second coil. By shortening the coil, you raise the frequency at which it operates. Using the whole coil will likely operate at broadcast frequencies. Selecting only part of the coil through this tap will give you short wave frequencies of some sort. I'd like to know what kind of circuit you have going on first, and why you feel it necessary to replace the original coil.
::::
::::Thomas
::::
::::::What article did I write? Can't find one on 8-15 that is all that interesting....just some replies and stuff.
::::::
::::::The coil you bought from AES probably is slug tuned, if you bought their universal oscillator coil. What is the original model number of your radio that you are converting to AC? Why, as you convert it to AC, did you need to re-do all of the circuitry? Why not either build a simple 117Z6 power supply with appropriate ballasts for the tube filaments (leaving in the battery tubes), or if tube substitutions must be made, and the radio is converted to AC complete with transformer, why must the circuits be modified extensively?
::::::
::::::If you have a new oscillator coil, and you're picking up short wave, then you have to go to Radio Shack and get their plastic alignment tool kit. Then figure out what the radio was originally designed to be tuned to. The IF transformers must be tuned properly first, and then the oscillator coil must be tuned to its proper frequency. This is done with the slug in the middle. Depending on the circuitry, a frequency may be chosen towards the middle of the dial, or the end, and then a padder condenser is used to adjust the other end of the dial. If your radio has only a trimmer on the tuning condenser, then you may want to adjust the slug until broadcast is received and somewhat in alignment, and then use the trimmer to synchronize the top end of the dial, and then go back and synchronize the bottom end of the dial with the slug. This process may have to be repeated several times. Depending on how well the tuning condenser matches up with the oscillator coil, you may have a little trouble. You may even have to change other components in the radio.
::::::
::::::What was wrong with the original oscillator coil? If you must use the 3 lug universal coil, connect the long half of the center tap to pin 5 of the 6A7 tube through a .0001 mfd condenser. Connect a 22k resistor from pin 5 to pin 6. Connect the center tap to pin 6. connect the short half of the coil to B-. Connect pin 4 to pin 3, and pin 3 to the RF screen grid supply. If this is the same as the B+ sent to the plates, then this is where it is connected. Usually the screen grids are fed through a resistor in AC radios. You are better off using the 6SA7G tube in place of the 6A7 tube, as it is appropriately designed for 3 lug oscillator coils. The 6A7 tube is designed for oscillator coils that have two definite separate coils. The large coil is used in the grid circuit, and the small coil is used in the plate circuit (grid 2 of the 6A7 tube).
::::::Thomas
::::::
:::::::Hi again
:::::::I am still working on the converted Zenith 4-v-31. It is a battery radio converted to 110v. I have everything just about right except for the oscillator circuit. The coil that was with the original radio seems to be actually two coils, one with a center tap. I bought a coil from AES, but it was certainly wasn't right, because, I turned the radio into SW! And it is not a SW radio. I am using a 6A7 tube for the osc/1st detector curcuit, but the schematic that I am using doesn't show me where or how the osc coil is hooked up in the circuit. I read with interst Mr Dermody's article posted 08/15, but would like a little more help. I am thinking about using a 5 tube schematic from Zenith and trying that, but it still doesn't show how to wire up the oscillator coil. Any help would be appreciated. Thanks
:::::You want the long version or short version? When I got the radio, it had been in storage for years. I could not read the number on the osc tube, but the socket had 6F7 on it. I run radio stations, and my engineer thought that the 6F7 was the right tube. When I put it in, of course, it didn't work. He suggested that we re-wire the radio, as the rest of it was not close to the original schematic. Since then, I got the old tube and discovered that it was supposed to be a 6A7. I got the schematic from www.gbronline.com\radioguy\index.htm, using the troubleshooting a superhetrodyne reciever. It used a 6A8 for osc. I couldn't get the coil to work, so I bought a new osc. When hooked up, I got SW. (wrong Frequency). But, it worked really well with SW. I then hooked up part of the old osc with half of the new coil, and it worked for just one station, but would not sustain oscillation. If cans are tuned properly (456). Still using original variable condensor and IF cans and antenna can. Using 78 for IF, 75 first det, 42 power, and 80 rectifier. The tech that converted the radio to 110 did not use same resistors, caps, etc. So since I did not have a schematic work with, I went to one that seemed to be close. Thats my story and I'm sticking to it. (ha)
:::::The radio was converted to 110 before I got it. (my grandmother's). The tech that did it did not leave a schematic and the work he performed did not match up on the schematic, (changed tubes, resistors,etc). The osc I bought does not have a slug. The original osc coil has four lugs, plus what looks like a center tap loose ( I used an ohm meter). I will see if AES has the 6SA7G that you recommend. Thanks
::By the way, it was a response to RCA AM band gone haywire, on 8\15. And, it was good.
OK, I have hooked up the original osc coil and I believe I have life. The "center tap" was not actually the center tap, but the end. Thanks so much for your help. You are truely an asset to all of us wantabe techs. I am sure I will have more for you as I have several other radios to restore.

9/21/2004 6:39:25 PMThomas Dermody

So the radio works fine now??????? Hmmmm. Cool.

:OK, I have hooked up the original osc coil and I believe I have life. The "center tap" was not actually the center tap, but the end. Thanks so much for your help. You are truely an asset to all of us wantabe techs. I am sure I will have more for you as I have several other radios to restore.

9/21/2004 6:40:47 PMThomas Dermody

How many terminals does that original coil have?

:So the radio works fine now??????? Hmmmm. Cool.
:
::OK, I have hooked up the original osc coil and I believe I have life. The "center tap" was not actually the center tap, but the end. Thanks so much for your help. You are truely an asset to all of us wantabe techs. I am sure I will have more for you as I have several other radios to restore.

9/21/2004 6:45:27 PMThomas Dermody

.......hmmmmmmm......that article.......Just wanted to let you know that I am no expert. Not even close. I am an amateur all the way.

9/21/2004 8:26:08 PMJohn Weeks

:.......hmmmmmmm......that article.......Just wanted to let you know that I am no expert. Not even close. I am an amateur all the way.
:
::How many terminals does that original coil have?
::
:::So the radio works fine now??????? Hmmmm. Cool.
:::
::::OK, I have hooked up the original osc coil and I believe I have life. The "center tap" was not actually the center tap, but the end. Thanks so much for your help. You are truely an asset to all of us wantabe techs. I am sure I will have more for you as I have several other radios to restore.
You might can fool some people, but not me. I am in the radio business, and I have visited alot of engineers, and believe me, I know you know your stuff. I would like to re-wire the radio back to as close to original as possible, and have an extra 78 tube, and may have a source for the tube socket. It would be cool to put it back to original, but I don't know where I can find the transformer Zenith used in the original 4-V-31. And the vibrator connection might be tough too. As you know, the schematic in Riders does not give a whole lot of info for the complete wiring diagram. The problem that seems to keep coming up is twofold, (1)voltage problem: the voltage varies almost every time I turn the radio on. The voltage to the field coil right now is 390 volts. The voltage after the field coil (B+) is 280. That's too hot for the filaments isn't it? the Heater votage is right (6.3)but of course the 100 volts and 200 volts are wrong as well. Now, tomorrow, it may be closer to 250.
(2) I don't seem to get enough negative voltage in the osc circuit to track the bottom part of the dial. I am willing to try your experiment if you would like me too, but it may take a little time. I restored a Silvertone 90volt radio\phono. Even "made" a 90 volt battery with 1.5 volt heater battery. I just finished with a 33 Crosley 148. That one was fun, because someone had added 3 40mfd caps and the radio did't call for any that big. Anyway, the point is that this Zenith is giving me fits compared to the others. Of course this one is mine, so that fits.

9/21/2004 8:37:14 PMJohn D. Weeks

:How many terminals does that original coil have?
:
::So the radio works fine now??????? Hmmmm. Cool.
::
:::OK, I have hooked up the original osc coil and I believe I have life. The "center tap" was not actually the center tap, but the end. Thanks so much for your help. You are truely an asset to all of us wantabe techs. I am sure I will have more for you as I have several other radios to restore.
:To answer your question, it has 4 terminals, and a loose wire. This is not to say it is the way it was from the factory, but the way it was when I started working on the thing.

9/21/2004 9:36:13 PMThomas Dermody

Well, if it has four terminals and a loose wire, then this is likely the original oscillator coil. The loose wire should be part of a coil. The larger coil should be divided into two parts--one smaller and one larger with a center tap joining the two. Read the original diagram for that radio carefully--it will give you an idea of what you're looking at. If it is in fact the original coil, you can wire the radio as it was originally wired (oscillator section) using a 78 tube in place of the 15 tube. If the oscillator coil does not in fact have a two part large coil, however, then it is not the original oscillator coil, which is probable since the radio was converted for the 6A7 tube. An oscillator coil with only 4 terminals--two to a large coil, and two to a smaller coil, is the right oscillator coil to use with the 6A7 tube, and since this tube is in here, someone could have pulled other parts out of another radio along with this tube to make the conversion.

What does your power supply consist of? You don't necessarily have to go back to the old vibrator system. Finding original parts will be extremely difficult. An AC system is more convenient. What kind of transformer is there? Is there an 80 rectifier tube in use? I don't know why the voltages would fluctuate unless the electrolytics were shorting or there was a poor connection somewhere. The 300 some volts you see in the power section is for the plate supply. The filaments have their own separate AC supply right off the transformer--6.3 volts. Do not confuse the two.

Also, if someone used higher value electrolytics in a radio than originally specified, this is okay--in the power section. It will reduce hum significantly. The only thing you don't want to do is put really high value electrolytics right at the cathode of the rectifier. The charge-up surge when you turn on the radio will blow the rectifier. With a 5Y3 or 80 rectifier, I wouldn't go over 40 mfd. If the radio originally called for an 8 mfd condenser, and there's a 40 mfd condenser, as long as the radio functions well, and the rectifier tube doesn't arc, all is well. I'd stick to around 20 mfd for a replacement of an 8 mfd condenser, though. 40 is a bit high, but will usually do.

What would really really really help a lot is if you carefully drew a diagram of exactly how your radio is wired NOW. This would hint out any mistakes made or anything else to consider.

Thomas

9/21/2004 6:37:42 PMThomas Dermody

Bare with me now.....I have some experiments for you to try. If these do not work, I strongly recommend that you change the radio back to its original state using 2 #15 tubes. The circuits I am about to discribe work best with a 6SA7G tube, but putting in this tube requires a socket change. The #15 tubes also require a socket change. The original circuit worked fine from Zenith, so it would be better, if socket changes are to be made, that you simply change back to the #15 tubes. They are 2.0 volt tubes with indirectly heated cathodes. If wired in series with eachother, and then a resistor, they can take the 6 volt supply from an AC transformer.

ACTUALLY!!!!!!!! What you could do is just obtain another #78 tube and a 6 pin socket. This tube is similar to the #15 tube, but its filament operates at 6.3 volts. You will have to tie the cathode and third grid together on this tube externally, as they are not connected internally. Using this tube and the existing 78 tube in the IF circuit, you could wire the radio exactly as it was originally wired. If you can get nowhere using the 6A7 tube, do this instead of converting it back to #15 tubes. It will allow you to use your original circuit diagram and oscillator coil. All will be balanced and matched.

6A7 EXPERIMENT

In trying these experiments, I want you to use your original oscillator coil. Establish top and bottom as shown in the original circuit diagram. To do this, look at the larger of the two coils--the one with the center tap. If the coils are wound as a single layer, this will be easy. If they are wound so that the turns overlap, then you must use the inside of the coil as one side, and the outside circumfrence as the other side. Wherever the smaller half of the large center tapped coil ends, we will call this bottom. We will use this reference for hooking up the smaller coil so that it is in phase with the larger center tapped coil. With your ohm meter, find the smaller half of the large center tapped coil. If it ends on the outside of the coil, this will be bottom. In reference to this, the side of the smaller coil (the one without a center tap) which ends on the outside of the coil will also be called bottom. If the former ends on the inside, then both the former and latter will have their bottoms on the inside. If, for any reason, you cannot get the oscillator circuit to oscillate, reverse the connections to the smaller coil. It is possible that you hooked it up backwards. In the last part of this experiment, where the small coil is omitted, of course you do not have to worry about this problem.

Take the bottom of the large center tapped coil (end of the smaller half) and connect this to B- (if the chassis is B-, then connect here). Connect the frame of the tuning condenser to this point as well. Connect the center tap through a .001 mfd condenser in parallel with an 8k resistor to the cathode of the 6A7 tube. This will be pin 6. Connect the top of the large center tapped coil (end of the larger half) to one side of the padder condenser as shown in the original circuit diagram for this radio. Connect the other half of the padder condenser to the stator of the oscillator tuning condenser (part of the gang tuning condenser).

Now, with the smaller coil (the one without a center tap), connect the bottom end to the B+ supply that supplies all of the IF transformer primaries. Connect the top half to pin 4 of the 6A7 tube. This is the second grid, also used as the first plate in an oscillator/converter tube. Pin 3 of the 6A7 tube should be connected to the same B+ supply that supplies all IF transformer primaries and the screen grid of the other RF tube. Pin 3 is the screen grid connection of the 6A7 tube. The grid cap on the 6A7 tube should be connected as originally shown in the original circuit diagram. Originally this would have been grid 1 of the #15 tube. Now it will be grid 4 of the 6A7 tube. This is part of the antenna circuit.

Connect, as originally shown in the original circuit diagram, the plate lead of the first IF transformer to pin 2 of the 6A7 tube. The plate lead is often colored blue, though it may not be. Connect the other lead of this primary coil to the B+ supply that supplies all of the RF tubes. This lead should be red.

Now here is where I find trouble. I do not know what to do with pin 5 of the 6A7 tube. This is grid one that is usually used in the oscillator circuit. Hook a 22k resistor from this pin to B-. Turn on your radio and align it. Align the oscillator trimmer (on tuning condenser) so that the dial synchronizes at 1400 kc, as originally specified. Then align the radio at 600 kc by using the padder condenser. If you are not able to do this, try connecting a .0001 mfd condenser from the top half of the large center tapped coil to pin 5 (grid 1) of the 6A7 tube. See if this does any thing in your favor.

If nothing above helps you, leave all connections done above alone (including the .0001 mfd condenser to grid 1). Short across the .001 mfd condenser and 8k resistor that lead to the cathode (pin 6) with a piece of wire. Disconnect the smaller coil from pin 4 and B+. Do not connect anything to this coil. Connect pin 4 to the B+ supply for the RF tubes through a 20 or 15k resistor. Proceed with the alignment proceedure.

Let me know what you come up with. Otherwise, if this fails, save your original oscillator coil and other parts. Obtain a 6 pin socket and 78 tube, and wire exactly as originally done when the radio was new.

Thomas

9/22/2004 12:31:02 AMNorm Leal

I didn't study the post but noticed #15 tubes were mentioned. You can use a #36 or #39 in place of a 15 without changing the socket. Only the filament needs to be wired for 6 volts.

Norm

:Bare with me now.....I have some experiments for you to try. If these do not work, I strongly recommend that you change the radio back to its original state using 2 #15 tubes. The circuits I am about to discribe work best with a 6SA7G tube, but putting in this tube requires a socket change. The #15 tubes also require a socket change. The original circuit worked fine from Zenith, so it would be better, if socket changes are to be made, that you simply change back to the #15 tubes. They are 2.0 volt tubes with indirectly heated cathodes. If wired in series with eachother, and then a resistor, they can take the 6 volt supply from an AC transformer.
:
:ACTUALLY!!!!!!!! What you could do is just obtain another #78 tube and a 6 pin socket. This tube is similar to the #15 tube, but its filament operates at 6.3 volts. You will have to tie the cathode and third grid together on this tube externally, as they are not connected internally. Using this tube and the existing 78 tube in the IF circuit, you could wire the radio exactly as it was originally wired. If you can get nowhere using the 6A7 tube, do this instead of converting it back to #15 tubes. It will allow you to use your original circuit diagram and oscillator coil. All will be balanced and matched.
:
:6A7 EXPERIMENT
:
:In trying these experiments, I want you to use your original oscillator coil. Establish top and bottom as shown in the original circuit diagram. To do this, look at the larger of the two coils--the one with the center tap. If the coils are wound as a single layer, this will be easy. If they are wound so that the turns overlap, then you must use the inside of the coil as one side, and the outside circumfrence as the other side. Wherever the smaller half of the large center tapped coil ends, we will call this bottom. We will use this reference for hooking up the smaller coil so that it is in phase with the larger center tapped coil. With your ohm meter, find the smaller half of the large center tapped coil. If it ends on the outside of the coil, this will be bottom. In reference to this, the side of the smaller coil (the one without a center tap) which ends on the outside of the coil will also be called bottom. If the former ends on the inside, then both the former and latter will have their bottoms on the inside. If, for any reason, you cannot get the oscillator circuit to oscillate, reverse the connections to the smaller coil. It is possible that you hooked it up backwards. In the last part of this experiment, where the small coil is omitted, of course you do not have to worry about this problem.
:
:Take the bottom of the large center tapped coil (end of the smaller half) and connect this to B- (if the chassis is B-, then connect here). Connect the frame of the tuning condenser to this point as well. Connect the center tap through a .001 mfd condenser in parallel with an 8k resistor to the cathode of the 6A7 tube. This will be pin 6. Connect the top of the large center tapped coil (end of the larger half) to one side of the padder condenser as shown in the original circuit diagram for this radio. Connect the other half of the padder condenser to the stator of the oscillator tuning condenser (part of the gang tuning condenser).
:
:Now, with the smaller coil (the one without a center tap), connect the bottom end to the B+ supply that supplies all of the IF transformer primaries. Connect the top half to pin 4 of the 6A7 tube. This is the second grid, also used as the first plate in an oscillator/converter tube. Pin 3 of the 6A7 tube should be connected to the same B+ supply that supplies all IF transformer primaries and the screen grid of the other RF tube. Pin 3 is the screen grid connection of the 6A7 tube. The grid cap on the 6A7 tube should be connected as originally shown in the original circuit diagram. Originally this would have been grid 1 of the #15 tube. Now it will be grid 4 of the 6A7 tube. This is part of the antenna circuit.
:
:Connect, as originally shown in the original circuit diagram, the plate lead of the first IF transformer to pin 2 of the 6A7 tube. The plate lead is often colored blue, though it may not be. Connect the other lead of this primary coil to the B+ supply that supplies all of the RF tubes. This lead should be red.
:
:Now here is where I find trouble. I do not know what to do with pin 5 of the 6A7 tube. This is grid one that is usually used in the oscillator circuit. Hook a 22k resistor from this pin to B-. Turn on your radio and align it. Align the oscillator trimmer (on tuning condenser) so that the dial synchronizes at 1400 kc, as originally specified. Then align the radio at 600 kc by using the padder condenser. If you are not able to do this, try connecting a .0001 mfd condenser from the top half of the large center tapped coil to pin 5 (grid 1) of the 6A7 tube. See if this does any thing in your favor.
:
:If nothing above helps you, leave all connections done above alone (including the .0001 mfd condenser to grid 1). Short across the .001 mfd condenser and 8k resistor that lead to the cathode (pin 6) with a piece of wire. Disconnect the smaller coil from pin 4 and B+. Do not connect anything to this coil. Connect pin 4 to the B+ supply for the RF tubes through a 20 or 15k resistor. Proceed with the alignment proceedure.
:
:Let me know what you come up with. Otherwise, if this fails, save your original oscillator coil and other parts. Obtain a 6 pin socket and 78 tube, and wire exactly as originally done when the radio was new.
:
:Thomas

9/22/2004 8:37:51 AMThomas Dermody

Well, Norm....what we have is a radio that has been converted to AC using parts from most likely another radio. Where there was a 15 tube in the oscillator circuit, there is now a 6A7 tube with 7 pin socket. I was suggesting that if he cannot get the original oscillator coil to work somehow with the 6A7 that he put in a 6 pin socket and put in a 78. He can wire the 78 like the 15 was originally wired, only it will have a 6.3 volt filament. The IF tube already is converted to a 78. Actually, though, I mentioned some ways to hook up the original coil to the 6A7, and if they don't work, another thing to try is to hook the top end of the small coil to the plate (grid 2) and the other end to B+ through a 20k resistor, as originally suggested. Then hook the bottom end of the large coil to B- (chassis), and the other end of the large coil to grid 1 through a .0001 mfd condenser. Place a 22k resistor from the grid to B-. Then attach the stator of the oscillator tuning condenser through the padder to this end of the coil prior to the condenser. With this arrangement, you'd use the entire large coil without connecting anything to the center tap.

The trick is to get the original coil, which is synchronized to the original tuning condenser, to oscillate properly with the 6A7 tube.

Thomas

9/22/2004 8:14:27 PMJohn D. Weeks

:Well, Norm....what we have is a radio that has been converted to AC using parts from most likely another radio. Where there was a 15 tube in the oscillator circuit, there is now a 6A7 tube with 7 pin socket. I was suggesting that if he cannot get the original oscillator coil to work somehow with the 6A7 that he put in a 6 pin socket and put in a 78. He can wire the 78 like the 15 was originally wired, only it will have a 6.3 volt filament. The IF tube already is converted to a 78. Actually, though, I mentioned some ways to hook up the original coil to the 6A7, and if they don't work, another thing to try is to hook the top end of the small coil to the plate (grid 2) and the other end to B+ through a 20k resistor, as originally suggested. Then hook the bottom end of the large coil to B- (chassis), and the other end of the large coil to grid 1 through a .0001 mfd condenser. Place a 22k resistor from the grid to B-. Then attach the stator of the oscillator tuning condenser through the padder to this end of the coil prior to the condenser. With this arrangement, you'd use the entire large coil without connecting anything to the center tap.
:
:The trick is to get the original coil, which is synchronized to the original tuning condenser, to oscillate properly with the 6A7 tube.
:
:Thomas

Hi guys
The original osc coil is working! The wire that I thought was the center tap turned out to be the end of the large coil. So, I attached the padder to the loose wire, and attached everything else to the coil, (wire with cap to grid 6A7, B+ to short coil to grid of 6A7), and it worked! Now I just have to get the voltage right. I need 250 B+, 200 for the plate on the 6A7, and 100 on the grid of the 6A7. I think I am about 25 volts off on the 100 and about 35 volts off on the 200 volts. Also, I am getting stations on the top end (1400, 1490) but nothing on the bottom end past 900. I know the padder needs to be adjusted, but where is a good starting point?

9/22/2004 8:18:42 PMJohn D. Weeks

::Well, Norm....what we have is a radio that has been converted to AC using parts from most likely another radio. Where there was a 15 tube in the oscillator circuit, there is now a 6A7 tube with 7 pin socket. I was suggesting that if he cannot get the original oscillator coil to work somehow with the 6A7 that he put in a 6 pin socket and put in a 78. He can wire the 78 like the 15 was originally wired, only it will have a 6.3 volt filament. The IF tube already is converted to a 78. Actually, though, I mentioned some ways to hook up the original coil to the 6A7, and if they don't work, another thing to try is to hook the top end of the small coil to the plate (grid 2) and the other end to B+ through a 20k resistor, as originally suggested. Then hook the bottom end of the large coil to B- (chassis), and the other end of the large coil to grid 1 through a .0001 mfd condenser. Place a 22k resistor from the grid to B-. Then attach the stator of the oscillator tuning condenser through the padder to this end of the coil prior to the condenser. With this arrangement, you'd use the entire large coil without connecting anything to the center tap.
::
::The trick is to get the original coil, which is synchronized to the original tuning condenser, to oscillate properly with the 6A7 tube.
::
::Thomas
:
:Hi guys
:The original osc coil is working! The wire that I thought was the center tap turned out to be the end of the large coil. So, I attached the padder to the loose wire, and attached everything else to the coil, (wire with cap to grid 6A7, B+ to short coil to grid of 6A7), and it worked! Now I just have to get the voltage right. I need 250 B+, 200 for the plate on the 6A7, and 100 on the grid of the 6A7. I think I am about 25 volts off on the 100 and about 35 volts off on the 200 volts. Also, I am getting stations on the top end (1400, 1490) but nothing on the bottom end past 900. I know the padder needs to be adjusted, but where is a good starting point?
Thomas, just read your reply. Will follow up with schematic for you. It may take a couple of days but will e-mail you. Thanks

9/23/2004 9:26:05 AMThomas Dermody

Well, first, you have the small coil hooked to grid 2, right? The grid that goes to the grid cap should be connected to the antenna circuit, not the oscillator coil. Grid 1 should be connected to the oscillator coil as I originally said, if you find this works. When you receive stations, are they synchronized with the dial markings? There generally is nothing below 540 kc, so if your circuits are way out of alignment, and your dial reads about 900 when you're in fact tuning around 540, then all you have to do is align everything. The trimmer on the oscillator tuning condenser should be set to 1400 kc by feeding a 1400 kc signal into the antenna circuit using a signal generator. When you tune your radio to 1400 on the dial (also 140 or 14 depending on how the radio is abreviated), you should receive this signal. Then turn the dial so that it reads 600. Set your signal generator to 600 and adjust the padder condenser until this signal is heard.

I have a question that really needs answering, though. How many parts is the large coil divided into? Is it just one coil or does it have a center tap? I need to know this information so I know if it is the original coil to the radio, or if it is a coil that was put in by someone when the radio was converted to AC.

The voltages you get on the oscillator tube may not be the voltages listed in some tube manual. Tube manuals state optimum voltages, and/or maximum voltages to operate a tube at. If you discribe how your power supply is laid out--AC voltage at transformer (high voltage winding which will likely be center tapped), how this winding is wired to the rectifier tube, what type of rectifier tube is in use, DC voltage at the cathode of the rectifier, filter condensers used after this, dropping resistors and field coil resistance including resistors that lead all the way to the different sections of the oscillator circuits, I can get an idea as to what causes your receiver to have the voltages it does, and what to do to correct any trouble.

Thomas
:
:Hi guys
:The original osc coil is working! The wire that I thought was the center tap turned out to be the end of the large coil. So, I attached the padder to the loose wire, and attached everything else to the coil, (wire with cap to grid 6A7, B+ to short coil to grid of 6A7), and it worked! Now I just have to get the voltage right. I need 250 B+, 200 for the plate on the 6A7, and 100 on the grid of the 6A7. I think I am about 25 volts off on the 100 and about 35 volts off on the 200 volts. Also, I am getting stations on the top end (1400, 1490) but nothing on the bottom end past 900. I know the padder needs to be adjusted, but where is a good starting point?

9/23/2004 7:10:36 PMJohn D. Weeks

:Well, first, you have the small coil hooked to grid 2, right? The grid that goes to the grid cap should be connected to the antenna circuit, not the oscillator coil. Grid 1 should be connected to the oscillator coil as I originally said, if you find this works. When you receive stations, are they synchronized with the dial markings? There generally is nothing below 540 kc, so if your circuits are way out of alignment, and your dial reads about 900 when you're in fact tuning around 540, then all you have to do is align everything. The trimmer on the oscillator tuning condenser should be set to 1400 kc by feeding a 1400 kc signal into the antenna circuit using a signal generator. When you tune your radio to 1400 on the dial (also 140 or 14 depending on how the radio is abreviated), you should receive this signal. Then turn the dial so that it reads 600. Set your signal generator to 600 and adjust the padder condenser until this signal is heard.
:
:I have a question that really needs answering, though. How many parts is the large coil divided into? Is it just one coil or does it have a center tap? I need to know this information so I know if it is the original coil to the radio, or if it is a coil that was put in by someone when the radio was converted to AC.
:
:The voltages you get on the oscillator tube may not be the voltages listed in some tube manual. Tube manuals state optimum voltages, and/or maximum voltages to operate a tube at. If you discribe how your power supply is laid out--AC voltage at transformer (high voltage winding which will likely be center tapped), how this winding is wired to the rectifier tube, what type of rectifier tube is in use, DC voltage at the cathode of the rectifier, filter condensers used after this, dropping resistors and field coil resistance including resistors that lead all the way to the different sections of the oscillator circuits, I can get an idea as to what causes your receiver to have the voltages it does, and what to do to correct any trouble.
:
:Thomas
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::Hi guys
::The original osc coil is working! The wire that I thought was the center tap turned out to be the end of the large coil. So, I attached the padder to the loose wire, and attached everything else to the coil, (wire with cap to grid 6A7, B+ to short coil to grid of 6A7), and it worked! Now I just have to get the voltage right. I need 250 B+, 200 for the plate on the 6A7, and 100 on the grid of the 6A7. I think I am about 25 volts off on the 100 and about 35 volts off on the 200 volts. Also, I am getting stations on the top end (1400, 1490) but nothing on the bottom end past 900. I know the padder needs to be adjusted, but where is a good starting point?
Sorry, I need to be more specific. The cap meant capacitor (.0001) from grid to oscillator coil. Everything is fine there. And, I meant that I was not getting stations below 900KC on the dial. But, now I understand what I have to do to track it. The oscillator is a four lug coil- two seperate coils with one coil having a center tap. The problem was that the radio was in storage for sometime and somehow one of the wires going to one of the lugs was broke. Only by close inspection did I find the broken wire. I put it back on the lug and, thinking that was the longest part, hooked it up for the ocillator circuit. Of course, it did't work. After ohmming it out, I found that the loose wire was actually the end(or beginning) of the longest coil. After talking with you, I changed to the original coil with the longest coil for oscillator and the shorter coil for B+ and it worked. I will now track with signal generator and get the bottom end of the dial to track. The wiring diagram you want can best be viewed by going to www.gbronline.com/radioguy/index.htm. This is the website for Bills Antique Radio. There is a section called restoration tips, hints, and kinks. In this section there is a section entitled troubleshooting a superheterodyne radio. I used the schematics for each circuit,(minus the power supply and RF amplifier). I used it exactly! Of course, the tubes I used were different, using the ones I have stated earlier. It called for a 6A8 for oscillator/detector. And so it called for two coils in the osc circuit. Now that I figured out the original coil, it sounds outstanding! My AM station KBST 1490, plays nostalgia music (big bands etc) so it was made for this radio. Now, the power supply schematic in the hints and kinks show a voltage divider that I will try tonite to get the voltage right. I have about 264 B+, 193 on grid 2 (coming off B+ supply with a 20k resistor), and 124 on grid 3-5,(Off B+ with a 20K resistor).Rectifier is an 80 tube, 369 volts off cathode, and 264 volts after field coil. Using 2-20 mf capictors on each side of the field coil, just like schematic calls for.