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