I called Mesa's customer service and described what was going on with my amp and he said he was almost positive it was a bad pre-amp tube and told me how to test them. I opened the chassis, replaced the V1 12ax7 and noticed that one of the power tubes was totally dark and the other one was pulsating with these weird flame-like flashes of light inside. So I pulled both of the EL84s and replaced them with some old Dutch ones that I got out of an old organ. This completely fixed it and the amp is working great. So now I have a few questions. Is it unusual for a power tube to go bad in a Mesa amp that is less than two years old? Could this be indicative of some other problem with the amp? Is it ok to leave these old EL84s in here for a while or do I need to get a set of Mesa EL84s in there? I don't know if these tubes are "matched", but if they are they were matched for an organ that took like 10 or so el84s. I previously had them in a Marshall using Yellowjackets for a couple of years and they worked great in that. I've read that Mesa amps are permanently biased so does that mean you have to use Mesa's tubes for optimal performance? And finally, who currently is making Mesa's tubes? Thanks!