Had a small gig in the weekend where my amp (WT800) was (poweramp) clipping horribly. The master wasn't even cranked and the cabinet (500w 4ohm ampeg) was farting like cabbage. Can low AC voltage cause this? I tried the rig later at home (admittedly with a different lower-spec cabinet) and couldn't get it to fart at all, no matter how hard I pushed it...
Oh, the hell yes. Eddie Van Halen used a Variac (AC voltage adjustment device) to run his Marshall Plexi's power tubes at 90 volts. This way, he got a lot more compression and distortion. Unfortunately, it also meant that he had to install a fresh quartet of EL34s every other week.