800c Sound Fades & Returns in One Channel

[Perkinsman]

After playing for an hour or two, it has an intermittent imbalance issue where the sound will "fade" away in the R channel. Then, after either a Volume or Balance control adjustment, the sound returns and plays fine for awhile & then repeats. It has been recently recapped, the tubes tested good & the power tubes are new JJ’s. Any clue as to what might be causing this unusual problem.

edit: The described problem ONLY occurs in AUX mode. Also, I’m not sure whether it’s related but when the volume is turned all the way down, I still get very low sound bleeding into the L channel on ANY function.

 

[tonyg88]

I wonder if your sound expander jacks are in too tight and are causing a short to chassis ground?

 

[Perkinsman]

Are those what I call the RCA input jacks, in this case the 2 AUX jacks? If so, I’ve cleaned them & compressed so they’re a little tighter around the input jack.
I’ve read many threads here where the Volume Control carbon wears out & causes odd problems. I’m wondering if that could be the issue here...the counter to that is that it only occurs on AUX

 

[tonyg88]

no the jumpers on top of the chassis I am talking about

 

[larryderouin]

What most people think are pre-out and main-in jumpers BUT AREN'T. An intermittent wouldn't be from the jumpers, but it's prudent to check them to make sure they aren't bottomed out in the jacks. It sounds more like a tube pin is intermittent. Pull each tube, re-tension the socket leaves and DeOxit the pins then immediately insert tube and rotate top in horizontal circle. You want the base to wobble in a circle so the pins pull out partially and then back in, scrubbing the pins and the socket leaves.

 

[Perkinsman]

Ok, pulled both of those jumpers & tightened/deox’d (again) each socket & it’s run for about 10 hrs without incident. So far so good! Thanks gentleman.

 

[tonyg88]

Damn now we will never know who was right just kidding but money would be on larry glad it has been working

 

[larryderouin]

I've got the same kind of intermittent in my X-101-B when it starts up. Worn socket. Retighten, and DeOxit usually improves conduction for about 6 months, Rinse - Repeat. One of these days I'll have to replace the socket, but right now too many projects around house (and garden) to make time.

 

[dsndblm]

I had a very similar issue with my TA 600. After a lot of chasing I reflowed all the input jack and speaker solder joints. Haven't had a problem since.