A small fan is fine.
Carl
KM1H
----- Original Message -----
From: "Pete N4KW" <n4kwpete@centurylink.net>
To: <amps@contesting.com>
Sent: Friday, November 28, 2014 10:43 AM
Subject: Re: [Amps] Holding a vacuum
Earlier this week I emailed Eimac with the question about shelf life of
the new 4CX1500B tubes that I have. I also asked about the serial
number on the tubes and how to read it.
I am awaiting the code for the serial number, regarding shelf life they
recommended that I at least apply filament voltage every six months. If
one was to apply filament voltage would a blower be required or not for
this tube.
73 Pete N4KW
On 11/27/2014 3:24 PM, Carl wrote:
----- Original Message ----- From: "Bill Turner" <dezrat@outlook.com>
To: "Amps group" <amps@contesting.com>
Sent: Wednesday, November 26, 2014 11:08 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
"It all depends" as they say.
Some ceramic/metal and glass/metal are notorious leakers such as the
4CX300A and PL-172 and PL-172A. Popular ones such as the 4CX150A
family, 8874 family, 8877, 3CX3000A, 4CX1000A/1500B hold vacuum well
but the indirect heated types such as the ones above (not the 3X3)
should be run up to 24 hours with just filaments to regetter from
outgassing. This includes the 8072/8121/8122 and long stored Russian.
Eimac had a couple of bad years in the late 80's with the 3-500Z when
they moved the plant to SLC; other than that they just had outgassing
as did most glass tube and need regular running with color to regetter.
The 3-1000Z and 4-1000A often went to air as well as did many of the
larger WW2 tubes such as 450/750 TH/TL, 6C21, and larger.
OTOH I have a pair of 1934-35 HK-354's that still run at a KW on AM
but other 20's to 30's TX tubes are almost impossible to find (mostly
RCA) with seals intact; 203A, 204A, 211, 849, 851, 852, and others.
Ive little to no experience with Russian and non US clone Chinese
tubes but have heard a lot of good things about Chinese
military/broadcasting ones in particular.
Carl
KM1H
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