I switched around the tubes in the mesa yesterday and found the sound to improve when running at 50 watts (the outer 2 tubes). This fact, also the fact that the amp seemed to sound much better, the fact that it sounds flabby, also that it sounds like a blanket is over the cab, and also that it was a floor model leads me to believe that the tubes are going. One tube even seems to look like it was burnt as the writing on it was brownish...and seem to be melting downward somewhat. Anyways ive had the amp for less then 6 months and wonder how do i go about getting the tubes exchanged under the mesa warranty? Hope its not a royal pain in the ***.