It's been a while... FOUND - Printable Version

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It's been a while... FOUND - Eric Adams - 09-12-2015

Since I've run across a problem like this. I have a 49-905 that I just finished replacing all the electrolytic and paper capacitors. All tubes and resistors check ok. My problem is a hum. It gets louder with the volume control but never over powers a station. I checked all the wires and they appear to be dressed as original. Even though the tubes tested good I swapped them out 1 by 1 with no difference.
Any help will be appreciated.

Schematic

Thanks,

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RE: It's been a while... - morzh - 09-13-2015

Eric

Hum can be anything.
Does it change with tuning or stays constant?

Now, often it is a result of bad ground. Look at rivets holding ground leaves where wire solder to. These are often the culprits.

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RE: It's been a while... - Eric Adams - 09-13-2015

It stays constant, but it doesn't drown out a station when I tune it in. It kind of stays in the background.
One more thing I forgot to mention. When I first got it completed, there was no hum. I aligned both AM and FM without a sound. I put it in the cabinet and played it for about 15 or 20 minutes and then it started. Does that help?

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RE: It's been a while... - Radioroslyn - 09-13-2015

Hey Eric,
I'd try swapping the tubes you may have gotten a cathode to control grid short internally in the tube. Higher voltage heater tubes are a little more suspect than others. As Mike said check grounds is good too.

Terry

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RE: It's been a while... - Eric Adams - 09-13-2015

Thanks, Terry. Tube swap has been tried. I'm just going to check all the grounds and recheck all of my solder joints.
I'll let you guys know how it turns out.

Thanks,

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RE: It's been a while... FOUND - Eric Adams - 10-03-2015

Well, I took it off of the punishment shelf for another look. I tried tube swaps again. It was the 19C8! I replaced it and the hum was completely gone.

Thanks for your help everyone.

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RE: It's been a while... FOUND - jerryhawthorne - 10-04-2015

Congrats Eric, one more off the punishment shelf.
Jerry

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RE: It's been a while... FOUND - klondike98 - 10-04-2015

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