6SN7 tube GTA vrs GTB

GTA: Max Plate Watts=5, GTB: Mpw=7.5
GTA: Rp=7700, GTB: Rp=6,700
Plate Current: GTA=9 mA, GTB=10 mA

The GTB was developed to handle 450 volts on the plates the earlier GTAs and GTs should really be biased down to 350 Volts. As for sound Only your ears will count. That said the GTB tends toward the warmer side and work well in an analytic system otherwise. The Old Stock 6SN7s are reasonably priced unlike everything else for audio and not including obscure Ham tubes. I would try a few different 6SN7s don't omit the GTs.
The GT are favored by many including me, the WGT is a tougher mil spec variant that I like as well. The Gts are popular and the demand is relatively high the good news is the the supply is enormous, thus fair pries. I have read that the 6SN7 was favored by the engineers due to their linear behavior. They were widely applied and many "millions" are out there. There is excessive demand for some of them, they are good no doubt, but the tube dejour are royally expensive.

I am not sure of what you consider "royally expensive", but I think I agree. I just paid $60.00 each for NOS Sylvania 6SN7s that are supposed to be "the" thing. I hope that they are worth it when they arrive.

Mechans

Very good info... many thanks for sharing your knowlege!

(http://home.att.net/~chimeraone/6sn7sound.html) I'm using the TungSol JAN CTL/6SN7GT bottom getter, round plate(not the mouse-ear) from the 40's as a driver and the Sylvania JAN CHS/6SN7W tall bottle(avoid the short bottle like the plague) as a phase splitter in my modded Cary SLM-100's. Couldn't be more pleased with the accuracy/dynamics and pure music that results. The less expensive but still excellent sounding alternatives are the Sylvania and Ken-Rad VT-231's(both 40's, bottom getters). That's if you enjoy clean, uncolored, no extra sweetening/warmed up sound. Otherwise the Raytheon, National Union and RCA VT-231 offerings may better suit you. Happy listening!