[Hallicrafters] Tube Tester Use

[Mark Shaum]

----- Original Message -----
From: "Bill Gerhold" <k2wh at optonline.net>
Subject: [Hallicrafters] Tube Tester Use


> I am now debating with myself if I should ignore the colors and
actually
> start to pay attention to the micromhos scale on the tester.

Well.. sorta.  Keep in mind that in most all oscillators and nearly all
amplifier functions where feedback is involved, a tube that shows, say,
80% of its "new" gain isn't going to perform any worse when in its
actual circuit when compared to one that is 100%.

I always found it interesting that when testing "new" tubes in my TV-7D,
which is also a mutual conductance/transconductance (same thing in
practice) tester, the new tubes nearly always read considerably higher
than the spec given in the military manual for the tube tester.  Yet the
"good" point, perhaps considered as a go-no go point by depot repair
staff, was entirely functional by the military requirements.

I'd really only worry about gain measurements if you are matching tubes
to be used in parallel, or if you read something less than 50% of the
tube manual published figures.  Even then it's likely to work fine.

And there are some tubes where testers don't give valid results, and
it's necessary to troubleshoot by directly substituting a "known good"
sample.  7360's in balanced modulators and mixers come to mind.

73! - Mark
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Mark Shaum K9TR
email: k9tr at dtnspeed.net
http://www.qsl.net/k9tr
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