[AMRadio] Testing big tubes

[wwd at netheaven.com]

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