NOS tubes are highly sought after by guitar players for our vacuum tube amps. We use a lot of tubes. There are web sites that specialize in NOS tubes. Mullards,Telefunkens, Brimars, RCA's and GE's sound dramaticaly superior to new Soviet and Chinese tubes. The Russian tubes have been improving and are "good enough" for most uses. The Chinese are mixed; many are microphonic and fail after several months. It has to do with the mechanical assembly and the rare earths used in the tubes. The factory skill set that was lost when the West shut down the production lines has not been recreated. Perhaps it never will be. For now there are good stocks of JAN (military)and old TV/Radio shop stocks to be worked out.
Why are NOS tubes considered superior?
The idea of "tube rolling" in my ARC preamp is something that I am considering. What I'm not sure I understand is the quality of tubes manufactured today vs. older tubes. It would seem that with modern manufacturing technology new tubes would be of higher quality than tubes made in the 60's and 70's. How are the older tubes better?