I’d be more worried about the caps than the tubes after 20 years in a box.
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i agree with the comments made
tubes rarely fail when stored... old capacitors are another matter
don't know where you are in the sf bay... i have a great tech who knows his way well around tube amps and can test tubes as well, in san rafael
(i personally have a very good tube tester as well, can easily test your 6sn7's)
message me if you would like the contact