An obvious anwer for testing tubes is s tube tester. Not just a basic emissions checker, but one that measures mutual conductance, leaks / gas, etc. I've read of specific recommended models in previous forum posts: use the search engine to find those rec's. I have an old Allied tester built from a kit but of course those are unavailable now. However a tube tester instrument is an investment only justifiable if you use it regularly, so save your money & check with Kevin at Upscale Audio or Underwood Wally for pretested 6922's that they feel would be a good fit for your application.
How can I test tubes?
I am auditioning hybrid phonostage AR PH3 and it seems that sound becomes too worm and dim during approximately 2 vinyl playback time. I need to know before I buy any new tubes if there is any way to test them first. There are SovTek660922 tubes in that phonostage.