6SN7 tubes

Thanks, everyone. Much appreciated. Goldeneraguy, a pair of 845B tubes is in the works already.

AFC, the 845 output tubes require a very high drive voltage (more than 200V peak-to-peak), in order to reach full power, therefore I assume that your amp must use 6sn7GTA or GTB, which can be operated at higher plate voltages.
Older 6SN7 tubes will work maybe for a month or two, then fail.

The 12au7 A suffix means controlled warm-up time, essential in series-connected TV heater circuits, not important in audio amps.
You will notice that the Telefunken Ecc82 tubes and most european 9 pin tubes flash when turned on. That is a sign of non-controlled warm-up...let's call it normal warm-up. No harm done, just enjoy the music.
If the Tele tubes sound a little bright in your system, Ecc82 tubes made by Philllips Holland, Amperex or Valvo do sound more "musical".

My preferences in terms of NOS 6SN7s are Sylvania brown base JAN-6SN7WA and the various Tung-Sol black plate versions. RCA GTA tubes are fine tubes too. I find the red base 5692 military tubes over-rated.
Because you are shooting for the best, I suggest that you bypass ECG Sylvania / Phillips ECG or GE 6SN7s, those tubes are well made and reliable, though not top audio performers.

Also avoid any late-production button-base 6SN7s. By the time those tubes were manufactured, the metal stampers were worn out and those tubes had become generic replacement/repair parts for old TVs.
good luck

Thanks, Casouza! Went with RCA JAN VT-231 tubes, the ones with grey glass. They're a little darker sounding, and are a good match.

You should try the Sylvania VT231's.

6sn7 should be properly matched with balanced triode-triode and tube-tube,not more than 10% with their transconductance and plate current.