Transformer and #80 tube

7/22/2002 10:59:12 AMJ-F

Hi, thank you all for your help. I found always an answer here! I want to troubleshoot my radio. I changed all caps by new ones. I checked all resistors and they are in the "tolerence" or near. But I have the same trouble like before. Big hum at all volume setting. What should I have at pins of 80 tubes? Pin 1-4, I have little more than 5 Vac, 2-3 I have 590 Vac. Should I have 5 V "DC" at pin 1?? There is a 15 MFD 350V on this pin with - to ground and + to pin 1. I have 3 other electrolitics on this radio with all - to ground (I supossed to put - to ground). Radio is Northern Electric 512. I think, hum is create near transformer and 80 tube. Maybe bad filtering, no? I'm not sure of what I do!! Thanks!

7/22/2002 5:46:11 PMNorm Leal

Hi J-F

Did you replace electrolytic filter caps? They dry out in time and cause hum.

Pin #1 should have high voltage DC when measured to chassis. Most radios would read 250-350 volts at this point.

Norm

:Hi, thank you all for your help. I found always an answer here! I want to troubleshoot my radio. I changed all caps by new ones. I checked all resistors and they are in the "tolerence" or near. But I have the same trouble like before. Big hum at all volume setting. What should I have at pins of 80 tubes? Pin 1-4, I have little more than 5 Vac, 2-3 I have 590 Vac. Should I have 5 V "DC" at pin 1?? There is a 15 MFD 350V on this pin with - to ground and + to pin 1. I have 3 other electrolitics on this radio with all - to ground (I supossed to put - to ground). Radio is Northern Electric 512. I think, hum is create near transformer and 80 tube. Maybe bad filtering, no? I'm not sure of what I do!! Thanks!

7/22/2002 7:21:26 PMJ-F

Hi Norm, yes I replace all electrolytics even than the other caps. All electrolytics have the negative to chassis. I did not take chance. But, I don't have a ground connect to chassis. Maybe I can replace the AC cord by new one with 3 wires to have the radio ground to earth.

:Hi J-F
:
: Did you replace electrolytic filter caps? They dry out in time and cause hum.
:
: Pin #1 should have high voltage DC when measured to chassis. Most radios would read 250-350 volts at this point.
:
:Norm
:
::Hi, thank you all for your help. I found always an answer here! I want to troubleshoot my radio. I changed all caps by new ones. I checked all resistors and they are in the "tolerence" or near. But I have the same trouble like before. Big hum at all volume setting. What should I have at pins of 80 tubes? Pin 1-4, I have little more than 5 Vac, 2-3 I have 590 Vac. Should I have 5 V "DC" at pin 1?? There is a 15 MFD 350V on this pin with - to ground and + to pin 1. I have 3 other electrolitics on this radio with all - to ground (I supossed to put - to ground). Radio is Northern Electric 512. I think, hum is create near transformer and 80 tube. Maybe bad filtering, no? I'm not sure of what I do!! Thanks!

7/22/2002 8:56:38 PMJohn McPherson

Hi,
Just a thought, but perhaps the capacitor case negative on one or two of the capacitors might need to be isolated from the chassis ground.

Were there any fiber washers, or bakelite isolators that did not get put back?

If they were omitted, and those caps attached to the chassis, when they are supposed to be insulated from the chassis- You would have a loud hum.

:Hi Norm, yes I replace all electrolytics even than the other caps. All electrolytics have the negative to chassis. I did not take chance. But, I don't have a ground connect to chassis. Maybe I can replace the AC cord by new one with 3 wires to have the radio ground to earth.
:
::Hi J-F
::
:: Did you replace electrolytic filter caps? They dry out in time and cause hum.
::
:: Pin #1 should have high voltage DC when measured to chassis. Most radios would read 250-350 volts at this point.
::
::Norm
::
:::Hi, thank you all for your help. I found always an answer here! I want to troubleshoot my radio. I changed all caps by new ones. I checked all resistors and they are in the "tolerence" or near. But I have the same trouble like before. Big hum at all volume setting. What should I have at pins of 80 tubes? Pin 1-4, I have little more than 5 Vac, 2-3 I have 590 Vac. Should I have 5 V "DC" at pin 1?? There is a 15 MFD 350V on this pin with - to ground and + to pin 1. I have 3 other electrolitics on this radio with all - to ground (I supossed to put - to ground). Radio is Northern Electric 512. I think, hum is create near transformer and 80 tube. Maybe bad filtering, no? I'm not sure of what I do!! Thanks!

7/22/2002 9:01:10 PMNorm Leal

Hi J-F

How loud is the hum? Background or louder than stations?

Your hum is caused by the power supply. Did all electrolytic caps originally connect to the chassis? Sometimes a negative connects to center tap of high voltage winding. Chassis and this point aren't always the same.

For a test, locate center tap of your high voltage winding. If it's not tied to chassis connect a negative side of a 10 mfd @ 450 volt electrolytic cap with positive to B+.

Norm

7/23/2002 6:12:00 PMJ-F

Hi! No, I don't have to isolate anything... There is no fiber washers or bakelite isolators. All is connect to chassis. It's the only ground. And the "hum" is louder than stations. I only ear that big sound and the speaker don't like that!! Is it important the place where I put the negative side of capacitor on chassis? Maybe the radio need only a big point of ground were all connect there? Or I can connect anywhere on chassis (ex: on any screws)?

Thanks, J-F

:Hi J-F
:
: How loud is the hum? Background or louder than stations?
:
: Your hum is caused by the power supply. Did all electrolytic caps originally connect to the chassis? Sometimes a negative connects to center tap of high voltage winding. Chassis and this point aren't always the same.
:
: For a test, locate center tap of your high voltage winding. If it's not tied to chassis connect a negative side of a 10 mfd @ 450 volt electrolytic cap with positive to B+.
:
:Norm
:
:
:
::Hi Norm, yes I replace all electrolytics even than the other caps. All electrolytics have the negative to chassis. I did not take chance. But, I don't have a ground connect to chassis. Maybe I can replace the AC cord by new one with 3 wires to have the radio ground to earth.
::
:::Hi J-F
:::
::: Did you replace electrolytic filter caps? They dry out in time and cause hum.
:::
::: Pin #1 should have high voltage DC when measured to chassis. Most radios would read 250-350 volts at this point.
:::
:::Norm
:::
::::Hi, thank you all for your help. I found always an answer here! I want to troubleshoot my radio. I changed all caps by new ones. I checked all resistors and they are in the "tolerence" or near. But I have the same trouble like before. Big hum at all volume setting. What should I have at pins of 80 tubes? Pin 1-4, I have little more than 5 Vac, 2-3 I have 590 Vac. Should I have 5 V "DC" at pin 1?? There is a 15 MFD 350V on this pin with - to ground and + to pin 1. I have 3 other electrolitics on this radio with all - to ground (I supossed to put - to ground). Radio is Northern Electric 512. I think, hum is create near transformer and 80 tube. Maybe bad filtering, no? I'm not sure of what I do!! Thanks!

7/23/2002 6:32:13 PMRuss Kincaid

You should be able to connect to any point on the chassis. Hum could be caused by a defective tube, filiment to cathode short. Also, a corroded connection at a rivited ground could be the problem.

:Hi! No, I don't have to isolate anything... There is no fiber washers or bakelite isolators. All is connect to chassis. It's the only ground. And the "hum" is louder than stations. I only ear that big sound and the speaker don't like that!! Is it important the place where I put the negative side of capacitor on chassis? Maybe the radio need only a big point of ground were all connect there? Or I can connect anywhere on chassis (ex: on any screws)?
:
:Thanks, J-F
:
::Hi J-F
::
:: How loud is the hum? Background or louder than stations?
::
:: Your hum is caused by the power supply. Did all electrolytic caps originally connect to the chassis? Sometimes a negative connects to center tap of high voltage winding. Chassis and this point aren't always the same.
::
:: For a test, locate center tap of your high voltage winding. If it's not tied to chassis connect a negative side of a 10 mfd @ 450 volt electrolytic cap with positive to B+.
::
::Norm
::
::
::
:::Hi Norm, yes I replace all electrolytics even than the other caps. All electrolytics have the negative to chassis. I did not take chance. But, I don't have a ground connect to chassis. Maybe I can replace the AC cord by new one with 3 wires to have the radio ground to earth.
:::
::::Hi J-F
::::
:::: Did you replace electrolytic filter caps? They dry out in time and cause hum.
::::
:::: Pin #1 should have high voltage DC when measured to chassis. Most radios would read 250-350 volts at this point.
::::
::::Norm
::::
:::::Hi, thank you all for your help. I found always an answer here! I want to troubleshoot my radio. I changed all caps by new ones. I checked all resistors and they are in the "tolerence" or near. But I have the same trouble like before. Big hum at all volume setting. What should I have at pins of 80 tubes? Pin 1-4, I have little more than 5 Vac, 2-3 I have 590 Vac. Should I have 5 V "DC" at pin 1?? There is a 15 MFD 350V on this pin with - to ground and + to pin 1. I have 3 other electrolitics on this radio with all - to ground (I supossed to put - to ground). Radio is Northern Electric 512. I think, hum is create near transformer and 80 tube. Maybe bad filtering, no? I'm not sure of what I do!! Thanks!

7/24/2002 1:17:21 AMNorm Leal

Checked the schematic. Important filters caps are the ones on each side of the speaker field to ground.

Try grounding top cap on your 75 tube. This will stop signal and may eliminate hum.. You can also try grounding Grid #1 on your 41 tube, pin #4. See if this eliminates hum?

Norm

:You should be able to connect to any point on the chassis. Hum could be caused by a defective tube, filiment to cathode short. Also, a corroded connection at a rivited ground could be the problem.
:
:
:
::Hi! No, I don't have to isolate anything... There is no fiber washers or bakelite isolators. All is connect to chassis. It's the only ground. And the "hum" is louder than stations. I only ear that big sound and the speaker don't like that!! Is it important the place where I put the negative side of capacitor on chassis? Maybe the radio need only a big point of ground were all connect there? Or I can connect anywhere on chassis (ex: on any screws)?
::
::Thanks, J-F
::
:::Hi J-F
:::
::: How loud is the hum? Background or louder than stations?
:::
::: Your hum is caused by the power supply. Did all electrolytic caps originally connect to the chassis? Sometimes a negative connects to center tap of high voltage winding. Chassis and this point aren't always the same.
:::
::: For a test, locate center tap of your high voltage winding. If it's not tied to chassis connect a negative side of a 10 mfd @ 450 volt electrolytic cap with positive to B+.
:::
:::Norm
:::
:::
:::
::::Hi Norm, yes I replace all electrolytics even than the other caps. All electrolytics have the negative to chassis. I did not take chance. But, I don't have a ground connect to chassis. Maybe I can replace the AC cord by new one with 3 wires to have the radio ground to earth.
::::
:::::Hi J-F
:::::
::::: Did you replace electrolytic filter caps? They dry out in time and cause hum.
:::::
::::: Pin #1 should have high voltage DC when measured to chassis. Most radios would read 250-350 volts at this point.
:::::
:::::Norm
:::::
::::::Hi, thank you all for your help. I found always an answer here! I want to troubleshoot my radio. I changed all caps by new ones. I checked all resistors and they are in the "tolerence" or near. But I have the same trouble like before. Big hum at all volume setting. What should I have at pins of 80 tubes? Pin 1-4, I have little more than 5 Vac, 2-3 I have 590 Vac. Should I have 5 V "DC" at pin 1?? There is a 15 MFD 350V on this pin with - to ground and + to pin 1. I have 3 other electrolitics on this radio with all - to ground (I supossed to put - to ground). Radio is Northern Electric 512. I think, hum is create near transformer and 80 tube. Maybe bad filtering, no? I'm not sure of what I do!! Thanks!

7/24/2002 5:42:56 PMJ-F

Hi, thank you all. You gave me some good hints. I will check that and will return if I need to. If you have other ideas, give them to me!!!

Thanks! J-F

:Checked the schematic. Important filters caps are the ones on each side of the speaker field to ground.
:
:Try grounding top cap on your 75 tube. This will stop signal and may eliminate hum.. You can also try grounding Grid #1 on your 41 tube, pin #4. See if this eliminates hum?
:
:Norm
:
::You should be able to connect to any point on the chassis. Hum could be caused by a defective tube, filiment to cathode short. Also, a corroded connection at a rivited ground could be the problem.
::
::
::
:::Hi! No, I don't have to isolate anything... There is no fiber washers or bakelite isolators. All is connect to chassis. It's the only ground. And the "hum" is louder than stations. I only ear that big sound and the speaker don't like that!! Is it important the place where I put the negative side of capacitor on chassis? Maybe the radio need only a big point of ground were all connect there? Or I can connect anywhere on chassis (ex: on any screws)?
:::
:::Thanks, J-F
:::
::::Hi J-F
::::
:::: How loud is the hum? Background or louder than stations?
::::
:::: Your hum is caused by the power supply. Did all electrolytic caps originally connect to the chassis? Sometimes a negative connects to center tap of high voltage winding. Chassis and this point aren't always the same.
::::
:::: For a test, locate center tap of your high voltage winding. If it's not tied to chassis connect a negative side of a 10 mfd @ 450 volt electrolytic cap with positive to B+.
::::
::::Norm
::::
::::
::::
:::::Hi Norm, yes I replace all electrolytics even than the other caps. All electrolytics have the negative to chassis. I did not take chance. But, I don't have a ground connect to chassis. Maybe I can replace the AC cord by new one with 3 wires to have the radio ground to earth.
:::::
::::::Hi J-F
::::::
:::::: Did you replace electrolytic filter caps? They dry out in time and cause hum.
::::::
:::::: Pin #1 should have high voltage DC when measured to chassis. Most radios would read 250-350 volts at this point.
::::::
::::::Norm
::::::
:::::::Hi, thank you all for your help. I found always an answer here! I want to troubleshoot my radio. I changed all caps by new ones. I checked all resistors and they are in the "tolerence" or near. But I have the same trouble like before. Big hum at all volume setting. What should I have at pins of 80 tubes? Pin 1-4, I have little more than 5 Vac, 2-3 I have 590 Vac. Should I have 5 V "DC" at pin 1?? There is a 15 MFD 350V on this pin with - to ground and + to pin 1. I have 3 other electrolitics on this radio with all - to ground (I supossed to put - to ground). Radio is Northern Electric 512. I think, hum is create near transformer and 80 tube. Maybe bad filtering, no? I'm not sure of what I do!! Thanks!