Hey Bob,
A couple of thoughts for you, just from my own experience. I've got a .22+ I bought new in '91. I've been experimenting with it more in the last year or so. I've tried 12AT7's, 5751's and 12au7's in v1 and v2. Some on here talk about great success doing this. I never really liked the results. I always got weird sounds and noises, and less dependability! Mesa Boogie told me changing the phase inverter tube to anything other than a 12ax7 wouldn't work well. I'd have to agree. I got more noise and increased feedback tendency. I haven't seen anyone talk about the fact that this amp can have a more significant tonal change by plugging straight into the "return" on the effects loop. This cuts out the entire preamp section except for the master and presence. You do lose the 2 channel foot switch thing, but I'm running my effects into my .22 this way, so I just switch off and on my overdrive in my effects. I generally use only reverb, delay and overdrive, so it works really well and gives me great EL84 power tube tone by itself. I have an effects unit that takes a tube, so I've got a 12au7 in there to lower gain. It does create limitations, but gets rid of all that heavy Mesa distortion, so I love it. The other advantage is, of course, instant ability to reverse the setup, back to "normal"! Mesa will send you a schematic for the lead drive mod upon request. Ask for Mike Bendinelli. I'd get you pictures, but mine doesn't have the mod. If you get the mod done, let us know how it works. Just my 2 cents!
