VAC 70/70 III Owners......6SN7, 300B Recomm.

I have owned 3 VAC 30/30's over the years, and have just upgraded again to the newest VAC Phi 30/30 which I am extremely happy with. I have stuck with the original 300B's for outputs, but have done much rolling with the 6sn7's in different positions. VAC runs all of the 6sn7's pretty hot in these amps, and they are 6sn7GTB's, which are designed to take the extra voltage. The driver 6sn7's are run with the most voltage, and the input tubes are run with a bit less, but still more than most non GTB tubes are designed for. That being said, you are better to run the GTB type as drivers. I have tried NOS Sylvania (1950's era) 6sn7 GTB's in the driver positions as well as the input positions. They will give you a tighter, stronger bass for sure, and a more forward, brighter presentation in the highs, sacrificing some "air" to the soundstage and making the amp less "lush" sounding. The highs were a bit brighter, but less sweet and extended. Then there are the wonderful sounding (non GTB) Sylvania VT231's from the 1940's... I tried them strictly in the input positions, not as drivers. They are more refined than the GTB's, with great bass, wonderful mids and plenty of extension in the upper highs, but not as forward as the GTB Sylvanias. They also have a faster, more lively sound than the stock tubes,
losing just a bit of "air" compared to the stock tubes, but not much. I have also tried Ken-Rads, RCA's, and many others, but preferred the stock tubes over them. If you find your 70/70 sounding a bit laid back or too lush for your tastes, try the 1940 and 50's Sylvanias. Hope this helps... Happy listening!

Thanks so much Bigshutterbug for responding! Anyone else have any experience they would like to share?

I have a pair of VAC Phi 70s and I like the sound so much I wouldn't touch the factory tube configuration. Then again, I'm biamping a pair of B&W Nautilus 801s using the Phi 70s for the uppers/midrange and a Krell integrated for the woofer. I'm using the 8 ohm taps out of the Phis (I tried the 4 ohm given the complex impedance curve of the 801s but the sound was ever so slightly polite and recessed compared to the other, so I switched back). This is a pretty nice setup, with a very open and airy top end (compared to solid state) that I don't find at all "romantic" or "lush". Maybe its not trying to use the tubes for the low end? I don't know.

My favorite 6SN7 combination, in my vac 70/70 mk3:

in this order:
--black glass KenRad, vt231 (6SN7GT): big deep sound, without sacrificing air
--black glass National Union vt231: very similar to above, maybe a bit softer, darker
--TungSol black glass, round getter: great tube, balanced, big sound, but not as big as KenRad; quiet.
--Sylvania VT231: sparkly, extended, but too bright with my speakers (Martin Logans). this might be the best tube with another speaker.
--GE 6SN7 GTA ... this is a great tube, well balanced, no major outstanding fault, and much more reasonably priced than the others (but also, lacking some of the magic of the above)
--electroharmonix... OK, kind of sterile, edgy.

300b
--The Golden Dragon's sound good in this amp! but,
--I liked the JJ 300bs even better... these sound GREAT in my amp. great extension, powerful sound. check out Eurotubes on the internet for good prices.
--don't waster your money on Western Electrics in this amp, I've tried them, and honestly, preferred the JJ 300bs. The JJs had better extension. The Western Electrics just didn't seem all that special, so I sold them, got most of my $$ back.

I recently purchased a VAC 70/70 mk3 s. where can I find more information about the tubes diagram for the amp? I know it uses two 6sn7 per channel. Are there any differences in functionality between the two 6sn7 used for each channel? For example, do I need to use a matching pair of 6sn7 per channel?

I have one matched pair of RCA red base 6sn7 and a matched pair of Raytheon vt231 6sn7. Can I use one RCA + one Rayheon vt231 for each channel? Thanks.

   "Can I use one RCA + one Rayheon vt231 for each channel? Thanks."      Yes and that's preferable, compared to using the exact same tube, in both positions.  

@rodman99999  Thanks. Do you know which sockets are which (splitter, driver) in the 4 sockets from left to right? Can't find that info in the manual. Thanks.