Hum and distortion from one channel in an 800-C

[angelaudio]

I have an 800-C that I got in non-working condition. It was not powering on so I immediately suspected the power knob as it wasn’t making the unmistakable “click” that it should. It is unrestored and it doesn’t look like anyone has ever done any work on it.

I proceeded to pull the power/volume assembly pot and could see a burn mark on one of the tabs


So I took a working volume/power switch from a donor 400 and soldered it into the 800-C. I powered it up on a variac and noticed that one of the AM 455KC transformers was arcing so I shut it off and clipped the leads that were going from the 455kc IF to pin 4 & 5 of 6HR6 which stopped the arcing. I then got all pots and switches cleaned up and after another listen I noticed heavy distortion, hum and less volume on the left channel.

I swapped the GE output tubes as well as the 12ax7’s and the problem persists. I toggled the tape monitor switch back and forth to no avail, same issue. Listening through the headphones made the distortion go away but the hum was still present. Sounds like 60hz hum. I have only listened through the aux using an iPod thus far and I’ve not tested the other inputs.


What could be the issue here?

 

[dcgillespie]

Anyone of a bazillion things, but let me ask one question: Does the hum, distortion, and reduced output go away when the input selector switch is set to (very specifically) the FM Stereo Filter setting? I realize that the FM section is no longer working to provide an audio signal in this position since you disabled the 1st IF stage, but you could still possibly at least notice if the hum is gone. Let us know.

Dave

 

[angelaudio]

Anyone of a bazillion things, but let me ask one question: Does the hum, distortion, and reduced output go away when the input selector switch is set to (very specifically) the FM Stereo Filter setting? I realize that the FM section is no longer working to provide an audio signal in this position since you disabled the 1st IF stage, but you could still possibly at least notice if the hum is gone. Let us know.

Dave

Dave, the hum is still present when in the FM Stereo Filter setting and gets louder with increased volume.

 

[dcgillespie]

Does the hum go to zero when the volume is full down?

Dave

 

[angelaudio]

Does the hum go to zero when the volume is full down?

Dave

The hum is still audible when volume is at zero although it is not as loud.

 

[angelaudio]

Dave, I cleaned the volume, balance and tone pots some more and the hum is gone now but the left channel is still weak and distorted. Could it have something to do with the volume pots?

 

[rg65]

My 800C just toasted the power switch and the power tubes are in poor condition along with several caps. Tech looking at it found to high of voltage to the power tubes which damaged the tubes and the power switch. The caps were all out of spec. I am not a tech but this may point you in the right direction.