I posted here a while ago and received a great amount of help with my pro reverb. Unfortunately I had to take it to a tech anyway. The original problem was , the vibrato channel was weak and distorted. I took it to a tech who has his own line of hand built amps. He had my amp for 3 months , then said I should blackface it , which he was sure would solve my problem. I agreed . He replaced the transformers , added a rectifier tube , installed a bias pot in the chassis , replaced all the electrolytic caps ....ect. he said it sounded good at first but then it got worse. Each time I called he said he was still working on it. Finally at 9 months he said he gave up on it. I picked it up . When I got it home I plugged in my biasrite probe and a new set of 6L6GC's. The bias instantly rose out of control and red plated the tube not in the probe. I quickly shut it down and tried another set of tubes. Same reaction only it was the tube in the probe this time. I tried adjusting the bias as the current kept rising. This had no affect at all. I realize it's impossible to diagnose this one without knowing verything the guy did , but I just need some help finding a starting point. He gave me a printed layout of the scheme he was using. It's an AB763 Super... Any help would be greatly appreciated.