6SN7 tube GTA vrs GTB


I would like to know the difference between the designation GTA and GTB.

Thanks
fordmod
(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!
Keep in mind if looking at the Sylvania JAN CHS/6SN7W(tall bottle, metal or black base): Some will try to pass off 6SN7WGT, GTB, or GTA's as the same tube. They're not even close in sonics. IE: (http://cgi.ebay.com/Two-1943-Sylvania-6SN7W-VT-231-6SN7-tube_W0QQitemZ320270099754QQihZ011QQcategoryZ73380QQssPageNameZWDVWQQrdZ1QQcmdZViewItem) CAVEAT EMPTOR!
It has been a journey for me to search for the "perfect" 6SN7s. I have 3 amps that use 6SN7s, and I tend to use GTAs and GTBs for driver tubes only. I have the following tubes for the gain stage and my summary is as follows:

Sylvania VT231s, bottom getters: clean, fast, accurate, and airy. My choice for classical music, but a bit thin for vocal music.

RCA VT231s, smoke glass: rich harmonics and sweet sounding, but a bit slow. It is great for vocal music, but not for complex classical.

Raytheon 6SN7GTs: nice sounding, but a bit too sweet for me

RCA 5692 Redbase: fast, rich, dynamic. It is excellent for Jazz and vocal, but not as good as Sylvania VT231s for classical music.

CBS 5692 Brown base: a tuned down version of RCA Redbase.

Ken-Rad clear glass: a bit too euphonic for me

Ken-Rad black glass: strong bass, but does not have the airy magic

Sylvania 6SN7GTs chrome top (not to be confused with GTA chrome top): my current overall choice, they are as fast and airy as Sylvania VT231 bottom getters, but have more sweetness.
I use Sylvania GT's and the ones known as (Bad Boys)in my pre. I can not find better.
(http://home.att.net/~chimeraone/6sn7sound.html) I've personally verified the findings of this site. That's why the TungSol JAN CTL round plates, and Sylvania JAN CHS/6SN7W(tall bottle) tubes have found a home in my system. None can deliver the music with less harm than they.