Pretty much any vintage 6SN7 (USA made) will blow away the russian/chinese ones. They range in price from the same as the current production junk to $60/ea. and everywhere in between. I'd suggest grey glass RCA 6SN7GT or KenRad, Sylvania, or National Union are all other good choices. Do a search - much info out there. (email me if you want some of the above types...)
-Ed
-Ed