Actually yes... No Joke... I understand the difference between a hard vacuum,
like a 3-500Z has and a "soft" vacuum.
I am just thinking that what may be useful, is to reduce the differential
pressure in/out of a tube. It appears that 3-500Z at 14 psi differential
pressure inside to outside, will last a couple of years or more before slow
seal leakage sufficiently violates the hard vacuum inside (If not
reconditioned regularly). If simple equipment could reduce the outside pressure
say, 3 orders of magnitude, (still far, far from a hard vacuum) then a
differential pressure change of 3 o 4 orders of magnitude might significantly
slow the ingress of gas through the seals, giving a much increased shelf life.
It appears that is what the Military vacuum packaged cans were doing for the
4CX250Bs, years ago.
[I just found a good site with explanations and numbers, which I am studying:
see: http://en.wikipedia.org/wiki/Vacuum#Examples ]
I dont know if it is easy to pull a vacuum 3 orders of magnitude from
atmospheric, which is very far from a "hard" vacuum. say, if atmos is 29.92"
Hg, then 0.29" Hg is 2 orders of magnitude less, I dont know if it is easy to
get to .29" Hg with ordinary pumps.
Best Regards,
73, de Pat Barthelow AA6EG
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Date: Fri, 30 Apr 2010 07:48:25 -0700
Subject: Re: [Amps] Tube Storage, vacuum containers
From: jimw7ry@gmail.com
To: sam@owenscommunication.com
CC: apolloeme@live.com; amps@contesting.com
Is this some sort of April fools joke?
Do you know what the vacuum is (how little air is actually) inside of a 3-500?
73
Jim W7RY
On Fri, Apr 30, 2010 at 7:30 AM, Sam Carpenter <sam@owenscommunication.com>
wrote:
I am surprised that the Russians are not doing that. In the past when I
purchased bulk eastern block machinegun ammo, it had always been packaged in
"sardine cans" that were pumped down and then painted and sealed. The stuff
from 60 years ago still had vacuum. I suppose you could silver solder a
refrigeration sealed system nozzle onto something and get an old pump used
for that and draw down a near perfect vacuum. That last inch or so takes a
long time but if you let it pump long enough, you can get there. I love that
idea for 3-500 or 4-1000. There will come a day we would surely appreciate
having done it.
Sam,N9FUT
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Patrick Barthelow
Sent: Friday, April 30, 2010 9:32 AM
To: amps@contesting.com
Subject: [Amps] Tube Storage, vacuum containers
Years ago I saw some vacuum packaged 4CX 250B tubes, at a military base MARS
station.
The 250Bs, were in OD green cans about half the size of a can of chili and
had molded plastic suspension inserts that kept the 4CX 250B softly floating
in the can. The can was evacuated, and when you needed the tube, you pulled
the pop top ring and pealed the top cover off the can, with the very
recognizable tseeeeeeeeee sucking sound of the broken vacuum the instant you
cracked the can open. I imagine that it would be useful for ham-consumer
use, if one designed a similar container to store a tube in, that you could
evacuate, and seal off, with ordinary (compressor in reverse) equipment.
Maybe one of those food vacuums that suck air out of plastic food (or for
that matter, clothing) containers. I dont think you would have to have
anything close to a perfect, or hard vacuum to be useful. If you lowered
the air pressure inside by several orders of magnitude, (I don't know how
much of a vacuum is easy to produce) with simple equipment and were able to
seal off the por
t, with the tube inside, the differential pressure inside the tube and
outside the hard vacuum tube would be reduced substantially, perhaps
substantially reducing the ingress of gas inside the tube over time. If a
ham had his set of spare 3-500Zs in the closet inside such a vacuum jar,
(periodically re cycled with the reverse compressor to keep the vacuum,)
the tubes, might have substantially longer shelf life, and he (and tube
makers) might buy such a kit accessory for their tube storage.... what say?
Best Regards,
73, de Pat Barthelow AA6EG
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