Help needed with Sears Silvertone Mod 7054 table radio.
This is a conventional 40's vintage table radio with AM band only which uses Loctal tubes. The schematic is available on Nostalgiaair.org as Riders 16-1. The problem is a loud garbled hum with weak reception in the background. At first it seemed like a classic case of bad filter capacitors but these had recently been replaced, however I replaced them again anyway. The hum still persists. I replaced all the capacitors after the detector stage. The hum still persists. When the coupling capacitor from the audio amp (7C6) is disconected, the output is as quite as can be. Touching the cap gives a loud response suggesting the output stage is working fine. All tubes check good with no indication of shorts. When I checked voltages of the RF, Osc, and IF amps, they are all normal and a distinct click can be heard above the hum when the contacts are touched with the VOM probe (coupling cap reconnected). This suggests the signal is getting through the coils, etc. I had seen this type of problem before with grid cap wires shorting out at chassis access holes but this set has no grid caps on the tubes. I am at a loss about what to do next. Any suggestions would be appreciated. Nick Senker, NJARC

Hi Nick

Replace cap C2, .005 mf, from pin #2 of your 7C6 to pin #6 of 50A5. If this cap has any leakage it causes grid #1 of the 50A5 to be positive. This in turn causes extra current to be drawn, hum and distortion.

http://www.nostalgiaair.org/PagesByModel/634/M0017634.pdf

Norm

:Help needed with Sears Silvertone Mod 7054 table radio.
:This is a conventional 40's vintage table radio with AM band only which uses Loctal tubes. The schematic is available on Nostalgiaair.org as Riders 16-1. The problem is a loud garbled hum with weak reception in the background. At first it seemed like a classic case of bad filter capacitors but these had recently been replaced, however I replaced them again anyway. The hum still persists. I replaced all the capacitors after the detector stage. The hum still persists. When the coupling capacitor from the audio amp (7C6) is disconected, the output is as quite as can be. Touching the cap gives a loud response suggesting the output stage is working fine. All tubes check good with no indication of shorts. When I checked voltages of the RF, Osc, and IF amps, they are all normal and a distinct click can be heard above the hum when the contacts are touched with the VOM probe (coupling cap reconnected). This suggests the signal is getting through the coils, etc. I had seen this type of problem before with grid cap wires shorting out at chassis access holes but this set has no grid caps on the tubes. I am at a loss about what to do next. Any suggestions would be appreciated. Nick Senker, NJARC

Just a quick thought: Loctal sockets are notorius for causing trouble: Try gently jiggling the RF section tubes or try cleaning the tube pins with an eraser or croakas cloth brush away the crumbs. Be careful not to burn your fingers.

MRO

Hi Nick
:
: Replace cap C2, .005 mf, from pin #2 of your 7C6 to pin #6 of 50A5. If this cap has any leakage it causes grid #1 of the 50A5 to be positive. This in turn causes extra current to be drawn, hum and distortion.
:
:http://www.nostalgiaair.org/PagesByModel/634/M0017634.pdf
:
:Norm
:
::Help needed with Sears Silvertone Mod 7054 table radio.
::This is a conventional 40's vintage table radio with AM band only which uses Loctal tubes. The schematic is available on Nostalgiaair.org as Riders 16-1. The problem is a loud garbled hum with weak reception in the background. At first it seemed like a classic case of bad filter capacitors but these had recently been replaced, however I replaced them again anyway. The hum still persists. I replaced all the capacitors after the detector stage. The hum still persists. When the coupling capacitor from the audio amp (7C6) is disconected, the output is as quite as can be. Touching the cap gives a loud response suggesting the output stage is working fine. All tubes check good with no indication of shorts. When I checked voltages of the RF, Osc, and IF amps, they are all normal and a distinct click can be heard above the hum when the contacts are touched with the VOM probe (coupling cap reconnected). This suggests the signal is getting through the coils, etc. I had seen this type of problem before with grid cap wires shorting out at chassis access holes but this set has no grid caps on the tubes. I am at a loss about what to do next. Any suggestions would be appreciated. Nick Senker, NJARC

:Hi Nick
:
: Replace cap C2, .005 mf, from pin #2 of your 7C6 to pin #6 of 50A5. If this cap has any leakage it causes grid #1 of the 50A5 to be positive. This in turn causes extra current to be drawn, hum and distortion.
:
:http://www.nostalgiaair.org/PagesByModel/634/M0017634.pdf
:
:Norm
:
::Help needed with Sears Silvertone Mod 7054 table radio.
::This is a conventional 40's vintage table radio with AM band only which uses Loctal tubes. The schematic is available on Nostalgiaair.org as Riders 16-1. The problem is a loud garbled hum with weak reception in the background. At first it seemed like a classic case of bad filter capacitors but these had recently been replaced, however I replaced them again anyway. The hum still persists. I replaced all the capacitors after the detector stage. The hum still persists. When the coupling capacitor from the audio amp (7C6) is disconected, the output is as quite as can be. Touching the cap gives a loud response suggesting the output stage is working fine. All tubes check good with no indication of shorts. When I checked voltages of the RF, Osc, and IF amps, they are all normal and a distinct click can be heard above the hum when the contacts are touched with the VOM probe (coupling cap reconnected). This suggests the signal is getting through the coils, etc. I had seen this type of problem before with grid cap wires shorting out at chassis access holes but this set has no grid caps on the tubes. I am at a loss about what to do next. Any suggestions would be appreciated. Nick Senker, NJARC
:
I did replace this cap, it had no effect. The plate on the 7C6 has only 4 volts! according to the schematic. Actually I measure a little higher, about 8 V Nick The set was very dirty, I will try the cleaning suggestion

Hi Nick

Cleaning sometimes helps. Loctal tube pins often make poor contact.

What type of meter are you using to read voltage? An older meter 1000 ohms/volt may read 4 volts on plate of the 7C6. These meters load down the circuit. If you are using a digital meter would expect closer to 50 volts as they have very little loading.

Voltage is supplied through a 2.2 meg to plate of your 7C6. There is also a .0001 cap, C19 to ground. Cut this cap lose and see if the problem goes away? If this cap becomes leaky you will hear a frying sound in the speaker. Resistor could have also gone up in value?

Norm

::Hi Nick
::
:: Replace cap C2, .005 mf, from pin #2 of your 7C6 to pin #6 of 50A5. If this cap has any leakage it causes grid #1 of the 50A5 to be positive. This in turn causes extra current to be drawn, hum and distortion.
::
::http://www.nostalgiaair.org/PagesByModel/634/M0017634.pdf
::
::Norm
::
:::Help needed with Sears Silvertone Mod 7054 table radio.
:::This is a conventional 40's vintage table radio with AM band only which uses Loctal tubes. The schematic is available on Nostalgiaair.org as Riders 16-1. The problem is a loud garbled hum with weak reception in the background. At first it seemed like a classic case of bad filter capacitors but these had recently been replaced, however I replaced them again anyway. The hum still persists. I replaced all the capacitors after the detector stage. The hum still persists. When the coupling capacitor from the audio amp (7C6) is disconected, the output is as quite as can be. Touching the cap gives a loud response suggesting the output stage is working fine. All tubes check good with no indication of shorts. When I checked voltages of the RF, Osc, and IF amps, they are all normal and a distinct click can be heard above the hum when the contacts are touched with the VOM probe (coupling cap reconnected). This suggests the signal is getting through the coils, etc. I had seen this type of problem before with grid cap wires shorting out at chassis access holes but this set has no grid caps on the tubes. I am at a loss about what to do next. Any suggestions would be appreciated. Nick Senker, NJARC
::
:I did replace this cap, it had no effect. The plate on the 7C6 has only 4 volts! according to the schematic. Actually I measure a little higher, about 8 V Nick The set was very dirty, I will try the cleaning suggestion

:Hi Nick
:
: Cleaning sometimes helps. Loctal tube pins often make poor contact.
:
: What type of meter are you using to read voltage? An older meter 1000 ohms/volt may read 4 volts on plate of the 7C6. These meters load down the circuit. If you are using a digital meter would expect closer to 50 volts as they have very little loading.
:
: Voltage is supplied through a 2.2 meg to plate of your 7C6. There is also a .0001 cap, C19 to ground. Cut this cap lose and see if the problem goes away? If this cap becomes leaky you will hear a frying sound in the speaker. Resistor could have also gone up in value?
:
:Norm
:
:::Hi Nick
:::
::: Replace cap C2, .005 mf, from pin #2 of your 7C6 to pin #6 of 50A5. If this cap has any leakage it causes grid #1 of the 50A5 to be positive. This in turn causes extra current to be drawn, hum and distortion.
:::
:::http://www.nostalgiaair.org/PagesByModel/634/M0017634.pdf
:::
:::Norm
:::
::::Help needed with Sears Silvertone Mod 7054 table radio.
::::This is a conventional 40's vintage table radio with AM band only which uses Loctal tubes. The schematic is available on Nostalgiaair.org as Riders 16-1. The problem is a loud garbled hum with weak reception in the background. At first it seemed like a classic case of bad filter capacitors but these had recently been replaced, however I replaced them again anyway. The hum still persists. I replaced all the capacitors after the detector stage. The hum still persists. When the coupling capacitor from the audio amp (7C6) is disconected, the output is as quite as can be. Touching the cap gives a loud response suggesting the output stage is working fine. All tubes check good with no indication of shorts. When I checked voltages of the RF, Osc, and IF amps, they are all normal and a distinct click can be heard above the hum when the contacts are touched with the VOM probe (coupling cap reconnected). This suggests the signal is getting through the coils, etc. I had seen this type of problem before with grid cap wires shorting out at chassis access holes but this set has no grid caps on the tubes. I am at a loss about what to do next. Any suggestions would be appreciated. Nick Senker, NJARC
:::
::I did replace this cap, it had no effect. The plate on the 7C6 has only 4 volts! according to the schematic. Actually I measure a little higher, about 8 V Nick The set was very dirty, I will try the cleaning suggestion.
:
Thanks Norm and others who responded. I continued to replace capacitors (paper type) and rechecking for hum after each replacement. While I didn't find any one capacitor that made a big difference, by the time I replaced all of them (except the mica ones) the hum was very much diminished. It appears the sum total of the caps were contributing to the hum. I am not usually a fan of indiscriminate recapping, but it proved useful in this case. Nick

Loop antenna missing? Connection to loop antenna broken? This will cause hum and garbled reception. Also look for inappropriate connections to the chassis. The chassis is isolated from the line cord by a condenser. Any connection from the non-switched AC line to the chassis will cause garbled hum. Shorts in any chassis and/or line cord associated condensers will also cause garbled hum.

Thomas

:Loop antenna missing? Connection to loop antenna broken? This will cause hum and garbled reception. Also look for inappropriate connections to the chassis. The chassis is isolated from the line cord by a condenser. Any connection from the non-switched AC line to the chassis will cause garbled hum. Shorts in any chassis and/or line cord associated condensers will also cause garbled hum.
:
:Thomas
:
An interesting comment Thomas; actually I have been working on the set without the loop antenna connected. When I touch the antenna lead going to the tuning cap with my finger I get pretty good reception but when I connect the loop antenna the reception is poor. I am aware of the isolation of the B- from the chassis but I will recheck for shorts. This agrees with my previous observations of shorted grid cap leads, etc. At this point all caps have been replaced except the micas. Thanks for your input. Nick

::Loop antenna missing? Connection to loop antenna broken? This will cause hum and garbled reception. Also look for inappropriate connections to the chassis. The chassis is isolated from the line cord by a condenser. Any connection from the non-switched AC line to the chassis will cause garbled hum. Shorts in any chassis and/or line cord associated condensers will also cause garbled hum.
::
::Thomas

Nick,

Have you tried adjusting the loop trimmer C3, I believe it is, for maximum on a station around 1500 KHz?

Radiodoc

::
:An interesting comment Thomas; actually I have been working on the set without the loop antenna connected. When I touch the antenna lead going to the tuning cap with my finger I get pretty good reception but when I connect the loop antenna the reception is poor. I am aware of the isolation of the B- from the chassis but I will recheck for shorts. This agrees with my previous observations of shorted grid cap leads, etc. At this point all caps have been replaced except the micas. Thanks for your input. Nick

:::Loop antenna missing? Connection to loop antenna broken? This will cause hum and garbled reception. Also look for inappropriate connections to the chassis. The chassis is isolated from the line cord by a condenser. Any connection from the non-switched AC line to the chassis will cause garbled hum. Shorts in any chassis and/or line cord associated condensers will also cause garbled hum.
:::
:::Thomas
:
:Nick,
:
:Have you tried adjusting the loop trimmer C3, I believe it is, for maximum on a station around 1500 KHz?
:
:Radiodoc
:
:I was looking at the alignment procedure which calls for adjusting trimmer C3 and I find the adjustment screw missing. I will try to find one to fit and adjust it for max at 1500 Hz. Nick
::
::An interesting comment Thomas; actually I have been working on the set without the loop antenna connected. When I touch the antenna lead going to the tuning cap with my finger I get pretty good reception but when I connect the loop antenna the reception is poor. I am aware of the isolation of the B- from the chassis but I will recheck for shorts. This agrees with my previous observations of shorted grid cap leads, etc. At this point all caps have been replaced except the micas. Thanks for your input. Nick

The loop will not work efficiently if its associated circuitry does not resonate properly with it. As Radiodoc said, tune up the antenna circuit--replace that screw. When you touch your finger to the grid side of the loop connection (loop absent), there's no resonance. You're just dumping in all of the stations (this is not true with loopless sets--ones that require a long wire antenna. In these sets there is still resonance, because they have antenna coils, small coils that work like the loop. The loop is a large antenna coil that also serves as the antenna). The oscillator is the only thing that is allowing the set to separate stations when the loop is absent. The stations are separated out because depending upon what frequency the oscillator is set to, only one incoming frequency matches properly with the oscillator frequency to create the IF (intermediate frequency). Having a tunable resonant antenna circuit, however, really helps things along, and makes the set more selective.

Thomas

:The loop will not work efficiently if its associated circuitry does not resonate properly with it. As Radiodoc said, tune up the antenna circuit--replace that screw. When you touch your finger to the grid side of the loop connection (loop absent), there's no resonance. You're just dumping in all of the stations (this is not true with loopless sets--ones that require a long wire antenna. In these sets there is still resonance, because they have antenna coils, small coils that work like the loop. The loop is a large antenna coil that also serves as the antenna). The oscillator is the only thing that is allowing the set to separate stations when the loop is absent. The stations are separated out because depending upon what frequency the oscillator is set to, only one incoming frequency matches properly with the oscillator frequency to create the IF (intermediate frequency). Having a tunable resonant antenna circuit, however, really helps things along, and makes the set more selective.
:
:Thomas
:The antenna (loop) wire is attached to the top of the tuning cap which appeared to have a screw missing; however under the chassis are where the trimmers are located on the bottom of the tuning cap. Adjusting the antenna trimmer with the loop attached made a big difference although there is still some anoying backgroung hum. Yhanks to all that have responded I have made sme real progress with this set. Nick