Disclaimer: This is my opinion only based on years of my own experience with both new tubes and so-called NOS and used vintage tubes from a variety of sources.
My personal opinion, for what it is worth, and that may not be anything at all, but, based from much personal experience owning tube audio components from a number of well regarded tube manufacturers, is that NOS and used vintage tubes offer absolutely no=zero=nothing=zilch=null=nada=nyet sonic or other advantage or value to the listening experience in pre/phono/power/guitar amps that I have owned, listened to or built. They are a waste of time and money while chasing a "holy grail" that simply doesn’t exist. For that reason, I am happy buying inexpensive new tubes from the Tubestore or the Tube Depot. I have NOS Mullards, Telefunkens, RCA, Sylvanias, etc., that I paid good money for along with new JJ’s, EH, Tung-Sol and Sovtek’s that, after much careful listening and comparing, hair-tearing and swearing, are as sonically fulfilling as any NOS or vintage tubes, despite what the "snake oil" sales guys or dealers will lead you to believe.
Again, this my personal opinion only from my own (possibly defective) ears and long term listening experience. Your mileage may (will) vary, of course. ;-)
My personal opinion, for what it is worth, and that may not be anything at all, but, based from much personal experience owning tube audio components from a number of well regarded tube manufacturers, is that NOS and used vintage tubes offer absolutely no=zero=nothing=zilch=null=nada=nyet sonic or other advantage or value to the listening experience in pre/phono/power/guitar amps that I have owned, listened to or built. They are a waste of time and money while chasing a "holy grail" that simply doesn’t exist. For that reason, I am happy buying inexpensive new tubes from the Tubestore or the Tube Depot. I have NOS Mullards, Telefunkens, RCA, Sylvanias, etc., that I paid good money for along with new JJ’s, EH, Tung-Sol and Sovtek’s that, after much careful listening and comparing, hair-tearing and swearing, are as sonically fulfilling as any NOS or vintage tubes, despite what the "snake oil" sales guys or dealers will lead you to believe.
Again, this my personal opinion only from my own (possibly defective) ears and long term listening experience. Your mileage may (will) vary, of course. ;-)