found this neat wee tip on www.talkbass.com and have been meaning to do it for a while and finally got around to it today.
Basically, what you do, is swap your drive tube in the pre amp (tube closest to the mid control) from a 12ax7 to a 12au7.
Wow, the results are unbelievable, instantly, the EQ becomes more apparent and much more responsive.
Seriously, those who know about this, try it, and those who don't, get on it and make your amp instantly better.
Before, I would find myself using the switch pulls to get good, round bottom end with defined highs, usually, my amp would be set at mid-7 bass-4/5 (sp) treble-4/5 (sp) with the input gain cranked to between 4 and 7.
Today after changing the tube, mids were at 8, bass was at 3 and treble was at 0 and it sounded better than it ever has before.
thanks for reading.