I am not an NOS tube aficianado. But I will say that in the output driver section of my c-j MV-55 power amp, I have tried various old American 6SN7's taken from my guitar amps,plus some originally store-branded NOS ones (probably of RCA manufacture) that I ordered from ATSI. Compared to the new Sovteks at $6 a pop (ATSI price), the differences were too small to worry over in my system (playing through Thiel CS2 2's). Much less to choose from here than in output or input tube selection (where I actually tend to disfavor Sovteks). I can only conclude that either the new tube is competent, or that in the driver position of this amp, at least, the choice is not critical. Whatever the case, they've been reliable, and are certainly cheap enough that it's painless to keep 'em in "to-spec" condition through regular replacement. But as you can tell, I'm one to avoid NOS anxiety wherever I can away with it - I find that doing so helps me to relax and just enjoy my music
