New Old stock...
>Were vacuum tubes ever used for any other purpose besides music?
Is there indeed a vacuum inside the tubes?
Like all electronics in the past... there used to be 100s of tube manufacturers.. radio, TVs ancient computers (before PC used too) all existed. Basically tube existed before solid state did. There used to be tons of manufacturers of tubes in the U.S and Europe. Now China, and Russia are the only places that make tubes... and really three factories... between them make most of your common tubes like Ecc83/12ax7s.
Best tubes? Amperex Matched Pairs of 12AX7as NOS is about 150$ a piece... Holland made. tightens up bass on a guitar amp niceley
more reasonably price... NOS American tubes from RCA and phillips made by various factories or Mullards (UK made) run 15- 30$ per tube.
My experience with tubes is mostly guitar amps, but I actually have all of these.