What goes wrong in tubes falls into a few categories, all of which a very modest emission tester can help you sort your spares so no bad ones linger. I mean, I do use weak 6BQ5s to sniff out issues in malfunctioning amps. Even the tube testers at stores like radio shack would not lie too much, very odd since the store often made money selling replacements.
My first tester was a Weston 798, a more complex mutual conductance tester that had bias setting/plate voltage/etc to make sure you accounted for the type of tube. i.e. rectifier, battery type, diode or triode-pentode. But that was old-school since I needed to add a 9-pin socket adapter to test 6CG7/12AU7 like a 6SN7 and 6V6/6K6/6L6 to 6BQ5 adapter among others. Basically the unit stopped at what ever tube was available in 1948.
Mercury, B-K, Sencore, EICO, Heathkit's simple emission testers are absolutely useful to triage tubes quickly. An open heater, inter-element leakage and gas is quickly detected using neon lamps and a modest meter for emission or grid-emission, a symptom of gas or loss of vacuum not severe enough to burn out a filament.
The Hickock and some expensive Sencore and B-K testers are used by serious audiophiles to nail down even tiny issues and are much more accurate on emission readings, as they actually bias the tubes' grid and vary the plate resistance for a "dynamic" test. They will even fire up an eye/bar indicator like a 6FG6-6E5-6AL7, which an emission tester will NOT do.
My Weston is go-to for old stuff, also my Supreme model 89 for pre-1940s tubes, but EICO 635 I built 45 years ago for the remainder, including compactrons.
A 625 is more comprehensive on old tubes as my 635 has no 4-5-6 pin socket for pre-40s tubes.
https://www.amateurradio.com/eico-model ... be-tester/ http://capeoldradio.com/cor_eico635.php
This EICO is cheap and it works to find BAD tubes and moderately weak ones, rarely is a tube not listed in its book. Forget the charts and adapters, just get a few testers spanning 1930s to 1970s and you can test anything.
