|[AMRadio] 813 question|
doxemf at aol.com
doxemf at aol.com
Tue Jan 31 20:13:57 EST 2006
Ed, et al
Recently to gain some shelf space and also determine what tubes were good or bad I set up a test jig using a 1Kv vaiable, regulated plate supply and an Eico 1030 H.V. supply for screen and bias with the heaters supplied from an HP 20V @ 20A variable CV/CC supply.
The 813s zero bias about 1kv and tests on 814s and 805s were also done.
These were of mixed NOS and Hamfest finds with the latter two types have visable getter marks which proved out as ythe faded getter tubes checked as gassy by lighting up like neon lamps at way below 1KV plate..
The 813s getter is rarely seen especially in the non metal plate versions so the only good way to check for a gassy condition is the test set or a working final but that method can lead to more serious issues if the tube just arcs out.
A real simple way to test these is an autotran controlled plate supply and a couple panel meters.
Simple to homebrew up using the same parts needed for building the final up. Or just in the actual unit without RF using the Variac for safety.
There were several gassy tubes found that I clearly remember having good getters when received 10 years ago or so. I figure that if there is still a reasonably good getter left then maybe a good burn in could degass the tube but if the getter is completely gone the is's too late.
From: Ed Swynar <gswynar at durham.net>
To: Discussion of AM Radio <amradio at mailman.qth.net>
Sent: Tue, 31 Jan 2006 17:28:57 -0500
Subject: Re: [AMRadio] 813 question
Those 813's are practically indestructable --- and I should know, too,
having used them in my amplifier for some 16 years now (only had to replace
the tubes ONCE!...and we're talking surplus/Hamfest jugs here, too)...
I have examples here of BOTH the graphite AND metal plates --- NO IDEA how
the metal plate versions retained the same "813" number --- it CAN'T
possibly be the same tube! --- but it has.
I have yet to use the metal ones, though...
Never could understand why guys spend the big $$$ for tubes --- albeit
modern, low drive, efficient ones --- when rugged, bargain basement bottles
like the 813 still abound...
~73~ Eddy VE3CUI - VE3XZ
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