I have two older 100W Marshall heads that I bring to rehearsal. Both of them experience the same issue. They cut out big time and/or don't work at rehearsal and then when I come home, they work fine. The only thing that is different is that I change from 8ohm at home (2x12) to 16ohm at reheasal becuase I use my friends 4x12 cab there. I've plugged straight in, tried different speaker cables, different speaker inputs, different cabs, different outlets, different guitar cables, different guitar, you name it! I've used my JMP 2203 most times and we eventually get it to work. Edit - (The 2203 had a seperate similar issue, but it has been resolved) Sorry about that. Yesterday I brought my 1975 Super Lead for the first time and it just kept cutting out or no sound at all. I even tried swapping 12AX7's. Yesterday it almost sounded like a blown transformer, but when I bring it home, it's fine! I was really bummin' yesterday thinking that the amp was cooked. WTF is going on? We even tried using my friends other 4 x12 cab, in a different outlet, etc and still the same results! This is the stangest thing I've ever encountered and it's really starting to piss me off now. I've wasted alot of time messing around with this too. Any ideas/help would be greatly appreciated. This is puzzling!!!!