[Amps] Holding a vacuum

[Roger (K8RI)]

On 11/26/2014 11:46 AM, Glen Zook via Amps wrote:

One example is the PL-172/8295A.  Basically the same tube and the PL-172 
has the 8295 designation as well, BUT the PL-172 is a metal, external 
anode, Pentode with the anode seal made of glass..  The 8295 is the 
ceramic/metal Pentode. Same tube but with ceramic seals.   The 
ceramic/metal 8295A brings a premium price. The PL-172s are notorious 
for getting gassy, while the 8295a are not.  The only ham amp that used 
them "that I know of" was the Hallicrafters HT-33A and KT-33B.  The 
straight HT-33 used a pair of 4CX-300 IIRC.

The PL172/8295A was a nice tube with a thousand watt dissipation 
rating.  It had a rather large anode, with a coarse fin structure that 
could run a KW, with just an open frame fan, or muffin fan.

73

Roger (K8RI)

> It depends!  There are certain tubes, like the 3-500Z, that are notorious for losing vacuum.  But, I have quite a number of glass tubes that were manufactured in the 1920s that are still fine.
> The ceramic tubes haven't been around as long as glass tubes.  But, those that I have, are still fine. Glen, K9STH
>
> Website: http://k9sth.net
>        From: Bill Turner <dezrat at outlook.com>
>   To: Amps group <amps at contesting.com>
>   Sent: Wednesday, November 26, 2014 10:08 AM
>   Subject: [Amps] Holding a vacuum
>     
> I'm curious as to your experiences with tubes in long term storage.
> The question is, which type holds a vacuum better - glass or ceramic,
> or is there no difference?
>
> My own limited experience says ceramic is better, but that is only
> with a few tubes.
>
> All comments welcome.
>
> 73, Bill W6WRT
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