This has been a long arduous amplifier repair. The previous owner had managed to botch a power transformer swap, dc filament modification, 6an8 to 12ax7 pi conversion, and filter cap job. Past that I'm not sure what else was or was wrong. I may be forgetting a few things at this point. Here's what I know. -This is the distortion model v4. http://www.ampegv4.com/images/VT22_Schem2.jpg -My new filament circuit is good. The power tubes receive AC and the preamp tubes are receiving just shy of 6 volts with a .1 volt ripple. -I've returned things to the 6an8 stock style phase inverter - When muted (grounded), I get a stable signal with functional controls all the way to the triode grid of the 6an8. -If I feed signal into the power amp in, things will wind up for a while and then there will be large clicking spikes (0:35 in) like LFO. -If I feed the signal into the normal input things are wildly unstable with the power amp included. They will stay in good shape to a point of volume. Any increase in volume past the point and you get this nightmare waveform. It tries to stay oscillating when I roll things back down. It's difficult to isolate anything since it's as though the entire amplifier freaks out when all parties are involved.