maxpudding
100+ Head-Fier
I had a “NOS” tube that went white on arrival. The seller quickly send a replacement tube.The best tester is the circuit it's being used in. Bottlehead has specific values of voltages when doing testing, as long as those are within limits the tube and amp are according to spec, nothing more nothing less.
Tubes in the crack will last a long, long time. Come to think of it, has anyone had a new tube fizzle out from use and needed replacement?