So I decided to have some fun rolling tubes in my little wonder. I have 2 stock Mesas, a JJ, a Sovtek and 2 vintage 1963 Raytheons. I will soon have a couple of Amperex tubes as well, but not until next week.
I was much more concerned with maxing my headroom than tone. I used a single passive bass with its' volume dimed, adjusted my eq as I always do these days (slight bumps at 200 and 1200 Hz, slight cut at 50), and found the point at which the overdrive was creamy, without delving into the buzz-saw, compressed range that I have no use for. I quickly found that the tube that drives the Mosfets is not the one limiting headroom, and it also has less influence on tone (but still some). I concentrated mainly on the preamp tube (the one closer to the jack). I realized I had oversimplified things in my head, thinking that each tube would shift from clean to OD at a certain gain level, but what I learned (as a real newb) was that the most significant difference between tubes wasn't where they transitioned from clean to furry, but rather how long each stayed in the creamy, useable (for me) zone before getting wildly hirsuit.
The Mesa tubes were the worst. They OD'ed early and shifted into wild buzz saw the quickest. The JJ was a little better but not much. The Sovtek and the Raytheons were the best. They both allowed me to push the gain to the 2 o'clock position easily and provided a lush, beautiful harmonic distortion that I dig. The Sovtek sounded bigger throughout the midrange and seems to have higher volume output (maybe 'cause it's new, although the Raytheons test near new). I'm not sure if I prefer the Sovtek or the Raytheons (BTW I have 2 of those and they sound and behave the same). However, they are both a significant upgrade over the stock tubes IME/IMO.
I'll wait for the Amperex pair and do another round of this next weekend.