The best one is the one that sounds the best in your amp (your circuit) and your system, to you. There is no best tube, in general, considering these criterium, as each tube will perform differently under these different conditions and also according to your own personal taste. Some people dislike Sylvanias, some 5692's in general and some RCA's (including the red line and base models). The only "Hall of Famer" that I am aware of is the Ken-Rad Vt-231/6SN7GT, but as to whether you would like the sound of it in your system, I don't know. Try running a search on 6SN7, 5692 and VT-231 at the Audioasylum.com tube forum and you will see what I mean. It will be fun reading nonetheless.
Edie, where is this 6SN7 going, and what function does it perform in your system? Also would help if you explain your reason for wanting to replace the current tube in that circuit ( microphonics, distortion, short life, etc.)
I am not an NOS tube aficianado. But I will say that in the output driver section of my c-j MV-55 power amp, I have tried various old American 6SN7's taken from my guitar amps,plus some originally store-branded NOS ones (probably of RCA manufacture) that I ordered from ATSI. Compared to the new Sovteks at $6 a pop (ATSI price), the differences were too small to worry over in my system (playing through Thiel CS2 2's). Much less to choose from here than in output or input tube selection (where I actually tend to disfavor Sovteks). I can only conclude that either the new tube is competent, or that in the driver position of this amp, at least, the choice is not critical. Whatever the case, they've been reliable, and are certainly cheap enough that it's painless to keep 'em in "to-spec" condition through regular replacement. But as you can tell, I'm one to avoid NOS anxiety wherever I can away with it - I find that doing so helps me to relax and just enjoy my music
Edle: Sorry, I just went to Audioasylum.com and the search feature will be down until Monday or so (they are re-vamping the site). When it comes up again, try searching under your specific amp and the type of tube and you should find many other user/owner comments on various combos (granted that you do not own an oddball one such as I do). Many of the posters will also have their systems posted in a separate area of the site, which will help you to understand where they are coming from. This is second best to trying the tubes yourself, but is a usefull aid.
The following are worth tracking down:
33S30(The absolute best,but almost impossible to find).
Syl. VT-231 metal base
TungSol VT-231 dark glass round plates
KenRad VT-231 dark glass
P.S. Try searching the old dejanews groups on the Google Beta feature.
Reylon- Great tube choices! However, I don't believe that Sylvania ever made the metal base VT-231. These were 6SN7A or 6SN7W metal base of the JAN-CHS- variety. Both the Tung-Sol and the KenRad VT-231 dark glass are excellent tubes as well; and though a little hard to find, are certainly less expensive than the metal base Sylv.
The last pair of Ken-Rad's that I tracked on Ebay went to Mr Blume of Coincident fame. He must like them in his setup, unless they were a gift for someone else. Yes, I am a busy body, so don't start.
I've tried Brimars, Sylvania green letter & VT 231, etc. The Ken-Rad JAN matched black glass VT231's that I have gone with in my pre line section are, together with the WE300B, the best tube I've heard overall. About $125/pr...enormously musical, spacious, dark and mysterious with the best bass, bar none. That is,if you can find them... The last Sylvania 6SN7W metal base CHS that I saw went for $300. Ouch.
I just recently upgrade my Supratek Chenin to Supratek Cortese mkII which is much more transparent hence differences between tubes can be easily heard. I tried Ken Rad black glass , big bass, nice presentation but not involving. Long time ago I have bought some NS grey glass 7sn7 - unbelievable what a change, tangibility, aliveness, transparency, huge dynamics, drive, drive. Different league.
After I have tried Sylvania metal base 6sn7W similar in scene, transparency but I have lost tangibility and drive.
Somebody told me that CV2821 is special, I was lucky to be able to find a pair. It do not have drive of NU grey glass I was not tapping my feet, but it have speed, transparency, resolution I never thought is possible with my gear.
If only I could have dynamics, slam of NU grey glass with speed , transparency of CV 2821.
A wealth of info here: (http://www.dehavillandhifi.com/6sn7_vt.htm). I found their results very accurate, having tried the top 10 favorites of the survey in my Cary monoblocks. The 1940's, bottom gettered Sylvania VT-231/6SN7GT, is a VERY nice(transparent) tube. The tall bottle, 6SN7W has more bass slam and a deeper sound stage.
I recently picked up some Sylvania three hole 6SN7T's from Dave Hollander. I'm using them in a pair of Octave Audio Amps. The tubes supplied by the manufacturer had no markings. So, I'm not sure what I replaced but the difference surprised me.
The Sylvania's three hole tubes produced a much better layered soundstage. I also was heard sounds at the rear of the stage more clearly. Previously these were masked. Finally, the transparency had increased from the front to the rear of the stage. Overall, the differences were not subtle and surpassed those of the supplied tubes and some Tung-Sols that I tried. I highly recommend that you give the Sylvannas a try.