I gigged a 100w Peavey Deuce combo troughout the 90's, it had 6L6GC tubes like the Valveking head. Allthough i cant speak for the preamp which was different on mine, the poweramp was pretty similar. It has huge headroom and Mesa-esque cleans, like peter said it has a very nice depth to it, filling up a hall very nicely, and the best part to me (then) wat that it took effects unusually well for a tube amp. I had it till it fell apart........
EDIT: the JSX seems to take 6L6GS tubes instead of the EL34's, could be interesting