Excellent tubes at a low price, highly rated in 'reference 6SN7 thread':

“More musical than the Sylvania Chrome Domes, rich harmonic structure with excellent imaging and sweet non fatiguing sound performance. Good imaging and low level detail resolution. Becomes a little too sweet in equipment that uses a lot of 6SN7 types. Nice combination with Sylvania Chrome Domes and the better 6SN7 “driver” tubes.” -Chimera The 1950's GT is a completely different animal than the RCA GTA or GTB from that period, in fact, it's pretty much the same tube as the 40's grey glass...