How expensive are best NOS tubes ? And how difficult to find ?

I too compared 6922’s 20 years ago, and I found that the best tubes were also the best bargains for what they were: HP branded. Back in the day, stories circulated that engineering students got part time work at HP testing tubes - and rejecting 95%. Let that sink in - rejecting 95% of NIB premium military tubes.

Guess that’s why the moon shots came off.

The best 6922’s were pinched waist Amperex until I discovered HP selected tubes, and the best available to me were the 1962 Telefunkens. These are so rare that most people have never heard of them, or even doubt their existence. Made the Plain Jane 1961 TF 6922 sound like garbage. I bought the last NOS sleeve of early HP/TF that I saw, back in ’98. Good luck finding more.

Speaking of 6922 tubes, try some  National Matsushita 7DJ8/PCC88 made in Japan new manufacture. The have replaced my Valvo Cca's sound great and are very affordable.

Very new to this game, just purchased my first tube pre amp. Been ss forever. My question is, what is the difference in plates on a tube? My pre calls for a 12au7 long plate. Are there any other "plates"?

The plates are the black or gray (usually gray) rectangular or square objects that take up most of the space in the tube. Long plates are usually found in older tubes, early (1950s) versions of tubes like the 12AU7. They may sound different from the later short plate or box plate or square plate (three different names for the same type of plate) versions of the tube but any 12AU7 socket that can use a long plate should also be able to use a short plate.

Tell us what brand of preamp you have and we may be able to help you get the right tubes in it.

Just purchased a Rogue Pharaoh integrated and am not familiar with tube jargon but read that "rolling" tube can be fun experiment if you know what you're doing.