I was noticing that I wasnt getting as much clean power as about a week ago, after our last gig. I checked the back of my Bass 400 while it was on and saw that one of the tubes (left center) looked like it was overheating. Most of the interior of this particular tube was orange-hot, while the rest of the tubes just had orange glowing filaments, like they are supposed to. I recently retubed my 6L6's to JJ's KT-88's and they have definately been running a lot hotter than my last set. I have my amp in a rack case and suspect that the built in fan, which is pretty strong, may not have been dissipating heat too well on the opposite end of the case. Any ideas? Does this sound like something wrong with the tube, or something wrong with the amp?