[Amps] Testing 8874s

[Bill Fuqua]

    I had a bucket  full of the Motorola conduction cooled tetrodes ( 
similar to 4cs250) tubes pulled from repeater and pager amplifiers. Got a 
deal on them, I thought, at a hamfest. Just about all of them were bad. It 
seems that commercial operators usually did not do anything until there is 
a failure.

73
Bill wa4lav


At 03:28 PM 11/1/2007 -0400, Joe Staples wrote:
>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
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