valve experts - 6sn7 suggestions?

VT231 is simply the military designation for 6SN7s. one and the same tube, ultimately. GTA, GTB, WGTA are all rated at 450v, I believe. Personally, I find the GTBs the worst of the lot, much preferred IMHO are the earliest ones: 6SN7w, 6SN7 GT, -WGT, and lastly GTA. About the only good GTBs are Tung Sol and perhaps a few select RCAs. There's many better sylvanias certainly than the later GTB stuff. (See above). GE isn't generally regarded as one of the choice NOS tubes to have, though certainly it's probably the equal of the chinese or Russian modern ones. Ones to seek out, IMHO: Ken Rad, Sylvania, Tung Sol, National Union, the earlier the better. Some of the 1945-52 Sylvania Tall-boys (bottom getter, tall envelope) and CBS/Hytron tubes are basically the same tube as the vaunted Sylv. vt-231, just w/o the military marking. Fortunately, there are a lot of good NOS tube choices in the 6SN7 family, and a fair amount of stock out there trading hands. have fun,
-Ed

Thanks for all the input. I can't wait to start experimenting with all the possible combinations. The PA160 mkII's have so many variables. Tweaker city, baby. Erik

Erik;
A real learning experience about the 6sn7's will start by paying a visit to Andy at V.T.S. (Vintage Tube Services)
He has a nice web page and is the authority when it comes to tubes of all sorts. He will soon be writing a book on tubes, and it should be one of the best around. He will straighten out any confusion about the voltage ratings and what you might need. I tried numerous Ken-Rads, Tung-Sols and Sylvanias from him, and it was an enlightening experience.
He has a great return policy, and will give you plenty of time to try out various ones. The Sylvanias have much lower
microphonics than the Ken-Rads and Tung-Sols, and are less "colored sounding" with the VAC amps. Happy tweaking!

Bigshutterbug (great handle),
Thanks for the lead. A valve return policy? Amazing. I have a buddy who has the same VAC's that I do. We are both benefiting from this thread. Again, thanks everyone.
Erik