Hi Carl:
I have found that tubes used in uhf and vhf applications normally will
still have plenty of good life in hf applications. This has been my personal
observation over the close to 50 years that I've been involved on commercial
land mobile work.
Cheers from Fern
Many used 8874's come from VHF/UHF commercial service and are pretty close
to dead by the time they are replaced. Shorted tubes usually come from hams
who have problems with overdriving and mistuning.
Carl
KM1H
----- Original Message -----
From: "Joe Staples" <w5asp@earthlink.net>
To: <amps@contesting.com>
Sent: Thursday, November 01, 2007 3:28 PM
Subject: [Amps] Testing 8874s
> 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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>
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