Help: Fender Pro Junior Undertones?

[uputthead]

I've got a strange undertone (sounds like a sub-octave pedal) when I crank my Pro Junior over about 4. I've switched all the tubes and tested on an auxiliary cabinet ruling out a bad speaker or tubes. I'm not super amp savvy, but I'm not afraid to dig in.

Does anyone have a clue what would be causing this wretched noise? Any input would be helpful.

Cheers

[uputthead]

Have I stumped the masses? Does this sound like a cap issue or possibly a rotery-gurder.... I'm retarded.

[pdf64]

That sounds like a power supply cap isn't doing it's job any more. It should be a quick job for a tech and as you're not amp savvy then that would be the best course of action. Minimum bench charge + $10 of parts hopefully. Peter.

[uputthead]

I'm tech savvy, just not amp savvy. How would I go about replacing that cap? Is it pretty simple? Where do I actually buy the part?

Thanks a million!

[darrellcheng]

read about amp safety, unplug, discharge, remove pot lugs, remove pcb screws, grab a schematic, identify caps, resistors, power supply/filtering caps (big gray caps).

Post some pics of the guts. The schematic will match up with the part numbers. www.ampwares.com will have the schematic