[Eric Adams]

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,

[morzh]

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.

[Eric Adams]

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?

[Radioroslyn]

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

[Eric Adams]

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,

[Eric Adams]

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.

[jerryhawthorne]

Congrats Eric, one more off the punishment shelf.
Jerry

[klondike98]