OK - So, I was out at a gig recently, and about 40 minutes into the gig, sound stopped coming out of my amp ... I'll spare the details, but I tried to think through all the possible issues, and deduced the problem was the head, and not some other part of my setup. I took it to a repair guy, he thoroughly checked it out, and told me there was nothing wrong, other than my state of being 50 bucks poorer. I had it out at a couple of other gigs ... all was well. Next gig, after about 40 minutes of playing, my sound just kind of faded away ... I could still hear myself, though faintly. My full volume returned after a minute or so. Happened one or two other times. The input light was registering an adequate signal entering the head. I took it back to the repair guy. He can't get it to fail, but for that matter, I can't get it to fail unless I'm at a gig, playing at a moderately loud volume for 40 minutes straight. The repair guy thinks it might have something to do with my cabs - that I'm not using the correct impedance, or that they are wired improperly. I've got two Avatar cabs - both four ohms. My head is rated down to 2. In both instances in which I've had problems, I've only used one of my cabs. I have never had a problem with this setup prior to these recent events, and I've had the same gear for a couple of years. So, could it really be my cab? It hasn't endured any drop or anything like that, and no one has messed with the wiring ... I'm at wits end here.