The 7591 tubes are available. Here's one place "Torres Engineering"

http://www.torresengineering.com/75newnewnewj.html

Actually, it slips my mind right now, but I think it is a variac. When a tube amp hasn't been used in a long while, you bring it up slowly to full power over a period of time to allow the capacitors to build back up.


"Those Who Do Not Learn From History Are Doomed To Repeat It" George Santayana