Mike Knudsen wrote:

I doubt there were ever walk-in tubes. The vacuum required for any kindof tube
life is so "hard" and pure that you wouldn't be able to pump out a whole room
to that purity. Though maybe with a really big "getter" ... Mike K.

I have this image of someone walking in through the airlock with a
_big_ container of cesium or strontium, to be used as a getter, and
hooking it up to a pair of terminals on the inside of the tube once
it has been baked and pumped down for a while.

I also have this image of an enormous induction heater, with coils
completely surrounding the tube, forepumps the size of modern fanjet
engines, and diffusion pumps slinging kiloliters of oil per second.

Somehow, I think it's just not viable.

--
I just overheard someone referring to Solaris 2.6 as a "virgin
operating system". With a straight face, no less. In one sense, I can
see it. The one whereby it knows what it wants to do, it's just not
entirely sure how... -- Carl Jacobs

In article ,
Mike Andrews wrote:
Mike Knudsen wrote:

I doubt there were ever walk-in tubes. The vacuum required for any kindof tube
life is so "hard" and pure that you wouldn't be able to pump out a whole room
to that purity. Though maybe with a really big "getter" ... Mike K.

I have this image of someone walking in through the airlock with a
_big_ container of cesium or strontium, to be used as a getter, and
hooking it up to a pair of terminals on the inside of the tube once
it has been baked and pumped down for a while.

I also have this image of an enormous induction heater, with coils
completely surrounding the tube, forepumps the size of modern fanjet
engines, and diffusion pumps slinging kiloliters of oil per second.

Somehow, I think it's just not viable.

I believe that in Rocket Ship Galileo, Heinlein discussed vacuum tubes
on the moon. No external envelope needed, just shielding.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott Dorsey wrote:

I believe that in Rocket Ship Galileo, Heinlein discussed vacuum tubes
on the moon. No external envelope needed, just shielding.

He did. Should make for _great_ transmitting-tube laboratories.

--
There are two product lines in which customers are called "users".
The other one is illegal drugs.
MWMeyer, viva voce personal communication

Mike Knudsen wrote:

I doubt there were ever walk-in tubes. The vacuum required for any kindof tube
life is so "hard" and pure that you wouldn't be able to pump out a whole room
to that purity. Though maybe with a really big "getter" ... Mike K.



I don't know about walk in tubes but I do recall visiting a UK Post
Office radio station many years ago and walking into the final
amplifier where there was at least one tube which I recall as being
around 4 or 5 feet high (maybe more) which had a water cooling system.
If it means anything to anyone the station was at Leafield in
Oxfordshire.

Dave

On Wed, 03 Mar 2004 22:47:32 -0500, Dave Holford
wrote:


Mike Knudsen wrote:

I doubt there were ever walk-in tubes. The vacuum required for any kindof tube
life is so "hard" and pure that you wouldn't be able to pump out a whole room
to that purity. Though maybe with a really big "getter" ... Mike K.

It's not that difficult.
Where I used to work we had vacuum chambers large enough for to get
in. We ran those down to 10^-7 torr.

OTOH we had some mass spectrometers that used ion pumps in addition to
the mechanical roughing pumps and the diffusion pumps.

Once past about 10^-2 torr, most of the molecules cling to the
surfaces and are basically scrapped off with the diffusion pumps.

After that there isn't a lot for the ion pumps as the things lasted
for years.

Course if we managed to burn out one of the induction heating coils
which was water cooled, it took days to clean up the mess.

You know it's gonna be a bad day whey there is water coming out the
roughing pump exhaust.

We once had a failure on the midnight shift that wasn't caught right
away. It filled up the entire exhaust system for a big room full of
float zone refining equipment. Now that was expensive.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com



I don't know about walk in tubes but I do recall visiting a UK Post
Office radio station many years ago and walking into the final
amplifier where there was at least one tube which I recall as being
around 4 or 5 feet high (maybe more) which had a water cooling system.
If it means anything to anyone the station was at Leafield in
Oxfordshire.

Dave