I'm having a problem with my WT-400 that I hope someone can help to diagnose. The amp had been working fine until I bought a new speaker cabinet. I did some shifting around of my rig, including the WT-400, in setting up the new cab. Now the WT-400 is giving me a distorted tone (especially on higher notes / strings). It also heats up VERY quickly -- withing 5-10 minutes of turning on the amp, the fan is already kicking in and the two phillips-head screws on the top of the head near the ventilation grill get extremely hot. Finally, it doesn't seem to be putting out the same power / output it used to. The problem is not with the new cab. It is identical to the old one which worked fine -- it's a 4 ohm 1210. I am only using one of the 2 cabs with the head, and I get the same problems here whether I use the old cabinet or the new one. Any ideas? Would a bad or loose tube cause symptoms like this?