This post brings me back a bit. One of my friends fathers worked for a
vacuum tube manufacturer (Eimac) and would patently explain any question
presented by one of the boys hanging out in his garage.
I remember him explaining that the silver you saw on the inside of a tube
was the last step in removing all of the oxygen from the tube. When the
tube had been pumped down and sealed off, there was a heating element that
would vaporize a but of silver and the vapor would bond with the remaining
oxygen and condense on the inside of the tube. The term for this was a
getter as it would "get" the last bits of stray oxygen.
This was the same guy that thought us how to drill a hole in glass using a
copper tube and a slurry of abrasive restrained by a clay dam. He also
explained why it was a real pain to drill stainless steel and showed us how
it could be done by holding pressure on the quill of the drill press with
one hand and using the other hand to turn the pulley. No destroyed bit and
no work hardening of the stainless.
--
Roger Shoaf
About the time I had mastered getting the toothpaste back in the tube, then
they come up with this striped stuff.
"Wild_Bill" wrote in message
...
Great video presentation, much better than any episode of the How It's
Made
TV show that I've seen.
Fire, and lots of shop-made metal parts to be observed. Resistance spot
welding and induction heating, too.
It looked as though the equipment he was using was all shop-made, and at
the
end of the video, it shows the guy making parts in a well equipped machine
shop.
FWIW, and contrary to popular belief, contained vacuum doesn't have to be
performed by using a vacuum pump.
When a vessel is heated to a high temperature, it's fairly well evacuated
of
air. Sealing the vessel/envelope while it's hot can be performed fairly
easily when the envelope is glass, whether it's a small vacuum tube or a
CRT.
A simple grade-school demonstration in the early 1960s involved dropping a
small burning piece of paper into a milk bottle, and placing a hardboiled
egg on top of the opening, as the flame went out.
That was a time when milk came in a heavy reuseable bottle with a large
neck.
Of course, this didn't demonstrate the evacuation process by external
heat,
it was just fun to see.
WB
.........
metalworking projects
www.kwagmire.com/metal_proj.html
wrote in message
...
Pretty interesting vid if you have about 17 minutes to kill.
http://blog.makezine.com/archive/200...ccum_tube.html
Dave