A buddy of mine was complaining his amp was blowing fuses. He used it at a jam on Sat night and the next day at home when he turned it on he heard a loud pop and the fuse blew. He said he tried another fuse and the same thing. I told him to bring it over and we would take a look at it for any obvious problems. I checked the tubes at the start and they didn't show any signs of excessive heat so I pulled the chassis and examines all the caps,resistors, diodes and wiring also looking for any traces of arcing or overheating. Now I am by no means an amp tech so everything was unplugged and grounded. No apparent problems with any of the components or wiring. So I turned it over and checked the power filter caps and again all looked good. He had the amp overhauled about two months ago and it was sounding good, by the way this is a real 65 twin reverb he's got here. Putting it all back together I asked him a few questions and he pointed to a tube saying it was really glowing the last time he blew a fuse. This was the first tube in the lineup of 4 6L6 GT's. I took that tube and swapped it with the third one. Then plugged it in and turned on the standby. Everthing seemed good the tubes started to heat up but I noticed the tube moved to the third position was not as bright as the others. This held for about five minutes then I turned on the standby switch and there was a loud pop as he described but also a wicked arc on the third tube. Of course the fuse was blown again and it was the last one. Before we put another one in I'm looking for some help. Could it be a bad tube??