[Amps] Testing 8874s

[Joe Staples]

We have an Alpha 78 (3 holer) which has a bad (shorted) tube and need a replacement.  We have found several 8874 tubes of questionable origin and unknown conditon.  What is the best way to if one or more of them is usable as a  replacement ?

We have access to another Alpha 78 which appears to have three good tubes (usually 1400+ watts into a Bird on 40 M).  Would swappng one of its tubes with an unknown and checking the effect on the power output be OK ?  (We're concerned that if an "unknown" tube is shorted it will crater the Alpha.)  Another alternative would be to remove all but one of the "good" tubes, check the power out (with low drive) and then replace it with an "unknown" ?

Any suggestions would be appreciated.  Unfortunately the "sick" Alpha lives in another country ... we need to known good replacement before leaving.

Thanks.

Joe, W5ASP