[AMRadio] Testing big tubes

[Bill Coleman]

Not sure how reliable this approach would be.... I have a few 4-400s that
work just fine at low power (1/2 normal HV, ~1600V on the anodes), but they
don't like full HV at all.

There was an article in one of the ham mags - or maybe a GE hamnote -
probably in the '50s, that described a test jig for TX tubes.  Basically an
oscillator arrangement. But I'm pretty sure it used close to nominal
voltages.  I filed my copy of it in a safe place - yes, gone forever.
~~~~~~~~~~~~~~~~
Bill Coleman    N2BC
http://home.stny.rr.com/n2bc
----- Original Message -----
From: <wwd at netheaven.com>
To: <amradio at mailman.qth.net>
Sent: Wednesday, May 22, 2002 10:07 AM
Subject: [AMRadio] Testing big tubes


> I've been collecting more 'spares' and 'collectible' transmitting tubes
> off eBay. Often the seller offers a money-back guarantee of xx days if the
> tube doesn't have ~full output. This is a kind gesture but raises a
> problem of how to easily test these to see if they are at least in the
> right ballpark. Opening up the big rig and removing shields to get at
> perfectly good tubes seems pointless just to run tests on newcomers.
>
> Has anyone seen a simple test setup to check cathode emission and element
> shorts while tube is hot? I'm thinking of a variac controlled B+ of no
> more than 800v for safety and simplicity. Would this give a good profile
> of a particular tube? Would it be enough to expose gassiness? Perhaps
> someone has seen an actual tube tester for power tubes or the schematic?
>
> It would be fun to run off curves at this low voltage to compare to those
> published by mfr.
>
> Bill    K2AME
>
>
>
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