In a message dated 3/28/2005 7:27:22 P.M. Central Standard Time,
W4EF@dellroy.com writes:
Someone asked me recently if the tubes in their Alpha 78 might
be going soft (they were measuring poor efficiency on 10 meters).
My response was to inquire about their measurement technique
in order to rule out measurement error, but the question got me to
thinking - are "soft" tubes a common problem in amateur service?
It is my understanding that cathode emission will commonly fall
off after a few years of 24/7 broadcast service, but this shouldn't
be an issue in amateur service since most of us use such low duty
cycles (a few hundred hours each year even with heavy contest
use). So the question is are there other common "soft" failure
modes that cause graceful degradation of tube output (as opposed
to hard failures)? I would be especially interested in hearing if such
failure modes are relevant to the Eimac 8874's used in the Alpha 78.
Thanks!
Mike, W4EF.............................
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And this brings up the question: Why would a soft tube show up on 10m
operation and not lower frequencies?
73,
k5gw
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