Mesa Triple Rec Problem...Help!
Ok, I'm going to make this as short as possible. Was on my way to practice and called a member to ask him to hook up my amp/cab and turn it on so it could warm up. I got there, plugged in and jammed for about 4 - 6 hours on it and it started sounding shitty, no tone, real muddy, ect. I check into it and find the head was running 8 ohms into the cab at 4 ohms. I replaced the 6L6s and 5U4GBs and everything sounded great again until about 20 minutes into jamming and the samething happened. I turned it off, cameback a couple hours later and samething, 20 minutes and it goes to hell. I'm thinking of replacing the 12AX7s cause they probably need it anyways but can anyone else think of something that could be causing this? My local music store said it sounds like a tube problem, but I already put 2 new sets (of 6L6s/5U4GBs) in it. Thanks.