Guitar Amp question

[Tubetec]

That appears to be a gut shot of the G40V ,
I dont know if it comes from the factory like this or not ,
it looks very scrappy to me , theres a good chance overtime the wiring like that develop interference issues if things move around .
Other than thats its a more or less a hardwired tube amp , with only a few corners cut ,
I saw another version of the G40V with conventional EI XFormers .

The new input socket with good grounding arrangements is probably the best first step , before trying to track down anything else , that alone could even solve the problems ,
Cable ties might be used to better support the wires ,away from each other in some cases , to reduce unwanted interactions ,
Using a wooden or plastic chopstick to poke around the wiring in an amp , while the input gain is up is the simplest method to track down signs of instabillity , often a wire and its proximity to another cause an interaction , if the effect is bad you can end up with a horrendous screechy sound , often it will vary with positions of the controls so the amp tends break into osccilation at higher volumes

 

[thecr4ne]

Ok, I finally got a chance to dig into this yesterday as I weathered the weather here in southern CA. And I have a new issue. It sounds like there's a very faint high gain version of the signal mixed in with the actual signal. It's not a hum or a buzz, it doesn't happen when the guitar's not playing, and it's very quiet compared to the actual signal, but it's definitely there. Any thoughts?

Here's what I did:

I replaced all the PSU filter caps, swapped out the input jack and added the 68K resistor there, Removed C9 and C21, swapped out R2 for a 100K pot for adjustable bias added 1 ohm resistors to pin8 on power tubes for bias measurement, and swapped out the olde chinese 6l6GC's for some NOS Jan 5881's I had around. Re-biased to about 34mA on each output tube.

Put it all back in the cab, fired it up and plugged in a guitar. Sounds great! Then...POP. (shit)
Switched it off immediately. Oh crap did I blow a filter Cap?

Opened it back up, turned it on again to inspect, and saw some fireworks under the PSU board. Pulled the board off the standoffs and suspended it to have a look at the underside and tried again. Turns out the power supply was arcing between traces on the PCB. Nice little burn mark (sorry didn't take a pic).

Called my olde man to discuss solutions, and after that consultation scraped off all the carbon from the scorch mark, and applied a coat of readily available brush on lacquer called "nail polish" (thanks wifey). It was even green, though not quite PCB green. Anyway I touched up the scorched spot with about 4 coats in total, and a few other spots that looked like the trace might've been slightly exposed just in case.

Fired it back up and no more fireworks. Cool. Still have the faint sympathetic signal though. Not sure where to start troubleshooting that.

 

[Voyager10]

Are you able to eliminate the loudspeaker (and everything mechanical) from your enquiries?

Also, do you have a signal generator (or phone with a signal generator app)? If the fault is audible with a continuous tone input it might be easier to locate.