JasonDW

Jason, Your amp is cathode biased ... self biasing. As long as the tubes are in the mid range ... 4-7 ... the amp will sound great and have the best tube life. 1-3 will run cold and sound grainy. 8-10 will run very hot, sound harsh, and have very short tube life. At 300 hours of playing if you change output tubes again you will notice a big improvement that you did not even realize was going on from a standpoint of fube and tone degradation. In Brad Paisley's amps we change the output sets every ten or so shows ... every 30 hours ... and notice a change. The again, some folks run EL84 tubes for years and don't seem to mind the loss of performance or tone. Myles, thanks so much for the reply. The amp really does seem to have renewed life with the new tubes. Unfortunately, I am noticing a very subtle "crackling" noise in the clean channel that wasn't there before. Is that something I should be concerned about? Is there a burn-in time with new tubes? By the way, the new tubes have a rating of (7). Thanks again, Jason

Hey Myles, I bought a new set of tubes for my Mesa Boogie Subway Rocket (2xEL84, 4x12AX7). They're groove tubes to replace the stock mesa boogie branded tubes that came with the amp 10 or so years ago. I poped the tubes in this evening and played for a while before it occured to me that perhaps I was supposed to have the amp rebiased since I switched brands, even though I didn't switch tube types. My questions are am I asking for trouble by not having the amp rebiased even though I replaced EL84s with EL84s and how would I know if I had a problem (would it be obvious)? Thanks, Jason

Myles, Thanks so much for your reply. Do any of these numbers mean anything to you? 6GH8A 5AM8 5N8

Hi Myles, I'm fairly new around here and people tell me I should address this question to you. Thanks in advance for your help: My grandfather, who turned 95 this year, is a retired electrician. A few weeks ago, when helping him move some things around in his basement, I opened a few of his old tool boxes and found several hundred old vacuum tubes. Being the owner of a couple tube amps, I'm intrigued by this discovery but digging through piles of tubes, I'm having a hard time figuring out exactly what I'm looking at. Specifically I found a whole bunch of tubes that look vaguely like 12AX7 pre-amp tubes. They're mostly from GE and RCA but I also found a Mullard and a couple Tung Sols. Unfortuntately, only a couple of them say 12AX7 on them. Most of them say 12AU7 and several of them have other designators that are greek to me. My question is, what is likely to happen if I pop a few of these into my Fender Blues Junior in place of the 12AX7s? Is it safe to experiment like that? Are 12AU7s interchangable with 12AX7s? Does anyone know where I can find a list of other tubes that are compatible with 12AX7s? Thanks, Jason