My usual rant is about people buying old desirable tubes as "NOS" that are used and pulled from other equipment. Nothing wrong with that, it’s cheaper to be sure, but you can run into issues sooner or later. Who knows how much life is in a tube that "tests" well? And is the buyer aware they are buying a used tube or one which the seller can’t warrant was never used?
Thankfully, I’m down to only a few tubes that are recherche. One is the 12ax7 and I just bit the bullet, bought two new sets that I know are new, not used, from ye old days, from reliable suppliers. I’ve been through the same thing recently with rectifiers, and they are at least double if not more, than what I paid 5 years ago if you can find them. Andy at Vintage Tube is probably one of the best sources in the US, but slow by comparison to other vendors.
I use a 6h30 where I can hear the difference between the more modern Russian production tube and the old stock DR Reflector. I lucked into a fresh quad of those. I use GEC KT 66s in my vintage system, good luck finding fresh examples of those- I may go to a modern tube in those amps when the time comes, simply because that system is not as critical.
Old tubes, particularly ones in demand by audiophiles, are harder to find and more expensive. I think the investment in a truly fresh example is worth the premium, but for some, it is stupid money. And there is equipment that is voiced to sound good using modern production tubes, which takes you out of the morass. It’s just another thing. To this hobby. That makes it more of a PITA. At least know what you are buying. (I never tried the Tesla copy of the "S" grade 12ax7).
