Well, I just picked up an old Ampeg SVT400T which is not producing any sound at all. HOWEVER, for some reason, it is ONLY producing sound when all of the knobs are MAXED out (turned all the way to the right) The amplifier IS turning on and the lights are working too. Even after the knobs are "maxed" it cuts out and the sound is gone after about two minutes or so. I can get my money back (I had one of these as a kid and wanted it for sentimental reasons) but I just wanted to know why it would be doing this in the first place. Thanks everyone!