I've noticed a noteable difference in the tone between some of the different tubes that Mesa has put in them stock (I had two identical WAs at the same time, one with Mesa Russian tubes and one with Mesa Chinese tubes), but the amps themselves sounded identical to each other to me when I tried switching the tubes between them. One difference that was recently noticed is that they changed the EQ sweep of the knobs for the parametric EQ for a short time for some reason (both of mine were from the period in the middle with the different sweep). But when set flat they should probably sound pretty much the same...
Thanks-that what I was hoping.I don't need another amp but....I took a test drive a few weeks ago and thought it sounded awesome!
From past experiences at the Mesa Boogie store I recall this thing being the opposite of my taste in tone, and sure 'nuff... 
