Well, I finally got my SVT, and messed with it a little yesterday and today. First impressions.....for all of the legend of the massive volumes, I was a little disappointed. It's loud enough for a band, but not much more. The sound also breaks up quite a bit into the svt "distortion" very quickly. If I dial the mids out, you can dime the amp and be at a pretty low volume level, but it cuts out the overdrive. I took the amp up to my bud cheezewiz to check out today, and I decided to take the back cover off to check things out. Well, there was the problem, I'm guessing. In the middle are 4 peavey branded 6550a tubes, and on both ends are sovtek 6550s. I suppose someone pulled their good tubes, and shoved whatever else they had in it before the sold it. The preamp tubes appear to be the original RCA's, and I see no reason to replace them. So needless to say, I am in the market for a new set of power tubes. The svetlana "winged c" 6550's are a likely candidate. I want something that will be close to an original SVT sound, but would also like to be able to drive it pretty hard without getting the buzzsaw distortion. I've read these winged c tubes are about as close as you can get to the originals, without paying and arm and a leg for OEM. Do the tubes need to be matched? Any references as to how to bias the tubes? I am somewhat handy, and would like to learn to do so myself.