Ive got one of the older triple rectifiers that I just starting having trouble with.
The other night when we had it cranked for a few hours the overdrive/distortion just kinda fell out. Like you rolled the gain knob way down. I talked to a friend and he thought it was tubes. They were pretty old so I just went ahead and put 5 new 12ax7s, 3 rectifier tubes, and 6 new ruby el34 power amp tubes. No change.
Further tinkering and found that it only does it with the orange and red channels. You can turn the gain knobs up from 0 to halfway, no issues, but turning it any more than that it starts fading away and the amp makes noise like am radio static. It doesn't do it on the clean channel, just both dirties. Anyone had this problem before?