Take it to a tech before you electrocute yourself. You don't have to calculate anything, just know how to use a multimeter. If you don't have that skill yet it's best not to be poking around in a tube amp.
Still a thing as in still being produced? No, not for quite a few years now. Your best bet at getting Fryette tones these days is with Synergy modules.
Gotta record at a slower tempo and speed up the tape like they did. :)
James can certainly play that fast. Lars seemed to find ways to cheat on every album.
JJ, russia, and china are making tubes as fast as they can, but not screening for quality as much. The shuagang plant has reopened. Tubes are out there, just be prepared to buy extras since they may not last long.