I built this amp a couple of months ago. It was my first attempt at a diy tube based stax amp. I have only 303s, so whatevever I hear is not going to be the last word in stax performance. Initial results were a little dissapointing. Everything worked, but the sound was thin, and the base was pretty weak. Not enough gain or voltage swing. Never the less, a stax amp with only two tubes and a transformer is a very attractive concept. I reworked the design so that the output tube is now a triode connected kt88 running at 580v on the plate ("pro" bias). The 6sl7 was replaced by a high gm 12gn7a (thanks, Pete Millett!) and the coupling is via interstage transformer. Huge improvement! Base, depth, and some real balls! Still brutally simple. I'm curious to see how it would compare to a "real" Stax amp. Definately worth a try if into diy Stax!