My girlfriend has a Mesa/Boogie 400+ (which i am incredibly jelous of), and today, she went to band practice, and i was hanging out there a bit. She goes to play, and the output is really quiet, and there's lot's of hum. We change cables, same thing. Replace her 9V in her bass, nothing changed. I check out the amp, and she had her amp outputing 4ohms into her 8ohm cab. Now, I told her that she needs to make sure she puts it in the right plug, because she's done this before. I said that it could destroy the amp, but it's less of a problem with tubes, but not much less. And for some reason, she took the "less of a problem" thing too far, and I suspect that for a while she's been doing this. At least once before, maybe more. The power tubes were bright purple, brighter than i've seen them, but with the fan on high they weren't hot enough to blow the fuse. Anyway, I'm starting to think that she's ****ed her power tubes. Any advice?