I have looked for a definite answer to this and have not found one. I played my amp the other night with no problems, but last night as I turned on the amp it just died on me as soon as I turned the standby off. There was no noise, pops, crackles, fizzes. It just turned off. I checked the main fuse and it was blown. I have not had any issues with tubes and they have not shown any signs of wearing out. I made sure my amp was connected to the cab correctly (remember i have had this rig for 8 years) and that I had a speaker cable rather than a guitar cable. I found online there could be issues with impedence and what not. I took the back off of my cab and noticed that a positive lead on one of my v30's became disconnected. I thought, 'Could it be?" So I reconnected it and replaced the fuse and the amp worked as advertised. I played for an hour or so and no problems yet. Could it be that the discoonnected positive lead on one speaker caused it to blow a main fuse?