You advice is very good, IF people will spend the money for ’real’ testers. I read very little about member’s tube tester results here. My friends don’t have them, they rely on me.
Can you give a short list of testers, perhaps a few to look for, and pick a current eBay listing or two of better ones.
Some newer tube amps have visible and external bias adjusters, many do not, sadly my early Cayin A88T adjusters are internal. Again, I suspect only those with external adjusters use them.
I got the info to adjust mine internally, including advice here, then chickened out and took it to Steve at VAS. When I was younger, I’d have been in there with metal! Joking, I would have left it unplugged a few days, left it unplugged, deoxit, twist back and forth, and left them physically mid-point (i.e. no meter, just guess): ’good enough, close it up!