Sam Carpenter wrote:
> 3-500z should be in the range of (pressure: Torr) 1×10−3 to 1×10−9
>
10^-3 torr is just a hard enough vacuum that the blue glow (ionization)
goes out.
Mechanical pumps are good for about 10^-1 torr which is about the point
where the tube "ignites", or the higher vacuum gages start working. By
the time you get to 10^-3 *most* of the ions are on the surface of the
tube and tube elements. 10^-6 is considered a good vacuum and can be
reached with the combination of normal mechanical pumps pulling on the
output of diffusion pumps using either 704 or 705 fluid. It's rare to
see vacuum beyond 10^-7 torr as that is headed into the realm of ion
pumps, gaskets made of pure gold, and cold traps using liquid Nitrogen.
It seems strange to pour the liquid Nitrogen into the trap and watch the
system almost immediately gain another minus 2 torr. The cold traps
only serve to keep the diffusion pumps from "back gassing". Older pumps
used liquid mercury that was boiled. Newer pumps use a silicone fluid.
Ion pumps actually absorb the molecules that are charged and accelerated
to the bottom of the pump. These pumps have no exhaust.
For those that are not familiar with diffusion pumps, they boil a fluid
with the vapor going up a chimney and then out deflectors so they come
down the inside wall of the pump which is water cooled. The vapor is
moving at supersonic speeds and *scrapes* the pump walls of molecules
and carries/pushes them to the bottom of the pump where they are
concentrated and then carried off by the mechanical pump. Supersonic
sounds really fast until you realize what the speed of sound is at 10^-6
torr.
The vacuum packed tubes are done that way to keep them dry and clean. It
may have some small effect on keeping them from getting gassy, but I
doubt they are even near 10^-1 torr.
I think you will find a tube that gets gassy only picks up the
occasional *molecule* of air and they slowly accumulate over time. But
there are poor seals and then there are really poor seals.
73
Roger (K8RI)
> Pressure Pa around 100 mPa to 100 nPa
>
>
>
>
>
> From: James Colville [mailto:jimw7ry@gmail.com]
> Sent: Friday, April 30, 2010 10:48 AM
> To: Sam Carpenter
> Cc: Patrick Barthelow; amps@contesting.com
> Subject: Re: [Amps] Tube Storage, vacuum containers
>
>
>
> 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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