[Boatanchors] Cooking in Old Transmitting tubes

[Geoff]

Since that is an indirectly heated tube running the filament only for few 
days may be the only method of regettering as long as the seals have held. 
Internal outgassing and loss of vacuum are entirely different events.

Since the Pentas were known to lose vacuum you may be wasting time but since 
its an almost free exercise....do it.

OTOH the Eimac should be much better in the vacuum department but should 
still be given a long cooking.

Run some small amount of air on the socket pins, the noisy blower isnt 
necessary.

Carl
KM1H


----- Original Message ----- 
From: "John King" <k5pgw at yahoo.com>
To: <Boatanchors at mailman.qth.net>
Sent: Thursday, January 26, 2012 7:36 PM
Subject: [Boatanchors] Cooking in Old Transmitting tubes


> Some of you knowledgeable transmitting tube folks who might have worked in 
> the Broadcast engineering field might be of service to me.
>
> I have just refurbished a 1958 or so Hallicrafters HT 33A Mark I that had 
> a Penta PL 172A transmitting in the socket when I got the amp. It is 
> beautiful NOW and the quality of possibly 50 to 60 year old tube is 
> unknown. I feel sure the original owner is dead because the amp looked 
> like someone had smoked a train load of cigarettes and blew all the smoke 
> into the fan on the amp. After two to three weeks of cleaning, it looks 
> almost new.
>
> My question is: It is presently getting the smoke test with filaments 
> turned on and I plan to leave it on for a long time or until it blows a 
> fuse. So far no smoke!!! What is the proper formula for bringing a LARGE 
> OLD transmitting tubes up after years of non use? I have no plate voltage 
> on it, only filament voltage and plan to leave it that way at least 12 
> hours or more.
>
> I have a Eimac 8295A that I am not POSITIVE is real good but it came from 
> a top notch Radio Tech's estate.
>
> I have a First Phone license but was not a transmitter Engineer when I 
> worked in Broadcast. That is why I would like to hear from someone with 
> the background.
>
> Thanks for your expert input and I will be listening. 73, John, K5PGW, 
> (Old Radio Geezer"
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