I was noodling around on the amp and all of a sudden, the volume drops DRASTICALLY...not silence, the amp was still amplifying, just not what it should. What equipment do I need to figure out what's wrong with it, is this equipment expensive, and can I use it for other stuff around the house? I have a bit of technical training, so multimeters are not foreign to me, but I don't want to shell out a bunch of money for new tubes if they're not the [likely] cause, and I don't want to shell out the dough for a tech to look at it if all it needs is new tubes. HELP!!!!