[AMRadio] 813 question


Jim Wilhite w5jo at brightok.net
Tue Jan 31 14:16:11 EST 2006


Don't know about the Russian tubes, but tubes shipped from Eimac had an 
instruction insert that said to burn in the tubes before applying power.

Since there is no such thing as a perfect vacuum a small amount of gas is 
left in a tube.  That is the purpose of the getter, to absorb those gasses. 
If I were installing a very old tube, say a 304 TL or 250TH or high power 
tube in a circuit, I would burn it in for at least an hour.  As I recall the 
instructions for the 4-X series of tubes called for about 30 minutes.

73  Jim
W5JO

----- Original Message ----- 
From: "Todd, KA1KAQ" <ka1kaq at gmail.com>
To: "Discussion of AM Radio" <amradio at mailman.qth.net>
Sent: Tuesday, January 31, 2006 12:37 PM
Subject: Re: [AMRadio] 813 question


>I haven't heard of this either. How would using them now suddenly
> prevent the adhesive from continuing to go bad, if it was really an
> issue?
>
> I suspect perhaps the reference is more in line with the big transmit
> tubes that sit around and either get gassy from sitting or have
> brittle filaments due to the metal composition. There are many
> references to these events happening, even with more recent tubes with
> respect to becoming gassy, and the recommendation to 'burn in' tubes
> that have been sitting inactive for any long period of time.
>
> Although I should add, the reason I heard for becoming gassy over time
> was due to molecules being released from the materials used within the
> tube itself moreso than leaking past pin seals.
>
> 813s seem to be the one large transmitting tube I have in excess as
> well, and none of them appear to have loose bases, whether used or
> NIB.
>
> de Todd/'Boomer'  KA1KAQ
>





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