The first thing to do! You need to get access or need to purchase a GOOD quality Tube Tester.
You can change caps/diodes, any or all the other parts in those amps, however, until you know the conditions of those tubes
you know nothing.
They may light up, again that tells you squat!
One shorted or severely weak tube in a group and all the other work done previously can go BANG.
You now have 20+ tubes and know nothing about them. Inserting a tube that's like 50-70% in with a group of 85%-95% means that tube does practically zero, except make the other tubes work harder, plus overtime it will drag the other tubes down with it.
There is my first suggestion. You need a decent Sencore / BK or Hickok late version tester.
I say late version because many testers out there will not test those sweep tubes effectively.
I actually have two different testers. When I test tubes, I check them in
both testers.
My 2 cents worth.
Yes, hold on to your wallet, good ones nowadays are not cheap! When you can find them in tested good working order.
http://alltubetesters.com/articles/tester_guide.htm
https://www.radiolaguy.com/Showcase/TestEquipment/Vintage Tube Tester Gallery.htm
My testers came from a Ham friends repair shop, I would never purchase one from eBay.
They need to be correctly calibrated and used frequently to be effective. IMHO
All the Best
Gary
