Friday while rehearsing I left my amp (a Sound City B120) on standby during rehearsal. After about half an hour we were ready to go and started to play, but first I got this horrible distorted sound (even on very low volume) and then the sound died... (the light which says that the amp is on does work though). Waited a day, took it home, tried to play it again, but still no sound. I checked the following things: Cab and the cord/cable with another amp (Little Bastard); everything works fine. the output tubes (all six of them) still glow nicely when turned on Can anybody help me diagnose the problem? A faulty pre-amp tube or is it worse? (When I bought the amp about two months ago it had undergone a compete checkup). Thanks in advance.