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.
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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.
Give 'em a pop quiz on Monday morning when they least expect it! Sorry, couldn't resist that. Bob is right...unless you're planning to buy bulk or try to find N.O.S. at an out of the way old T.V. repair shop, buy from a reputable and knowledgeable dealer. As the price goes up, so does the counterfitters' motivation! You might also check out to be very well versed with an increadible selection. Good luck!