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@outlook.com>
To: Amps group <amps@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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