Ok, I did a search but my problem is a little different. My 3500 head hisses when you turn the tube preamp up (at all) and pops. The closest sound to it would be cooking bacon on a frying pan! I saw threads about turning the faders and high contour knob down, but i have to cut ALL highs to get rid of the hiss. The pop however remains, just sounds like dull thuds though. I've had the amp for 4 years and it may have been turned up too loud by friends at some stage 2 years ago when I wasn't with them when they used it. Also a couple of months ago my girlfriend turned my head on without any speakers plugged into it and turned everything on the head up. When I saw it after she had turned it off, I plugged my bass in to scope the damage. The amp hissed a lot, but after a few days it went back to "normal" (the hissing and popping described above). So I guess my questions are: 1. Could it just be the tube? 2. Could my amp be broken beyond repair ( ) 3. Can I fix this myself?