Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!mcgill-vision!snorkelwacker!usc!wuarchive!zaphod.mps.ohio-state.edu!ub!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: Ridiculous Impedance
Summary: Glass to metal seals on vacuum tubes...
Message-ID: <4022@kitty.UUCP>
Date: 12 Sep 90 14:47:02 GMT
References: <1770009@otter.hpl.hp.com> <1770013@otter.hpl.hp.com> <1990Sep12.035908.6083@mlb.semi.harris.com>
Organization: Recognition Research Corp., Clarence, NY
Lines: 24

In article <1990Sep12.035908.6083@mlb.semi.harris.com>, del@thrush.mlb.semi.harris.com (Don Lewis) writes:
> >	Despite the existance and use of transistors during the 1950's,
> >the TAT-1 undersea repeaters all used vacuum tubes.  If memory serves me
> >correctly, these vacuum tubes had flexible stranded wire leads which were
> >soldered directly into the circuit - with no connectors being used.
> 
> How did they produce a vacuum tight seal with stranded leads, or were the
> leads connected to some sort of solid wire feedthrough?

	I believe the stranded leads were welded to solid metal posts
which actually penetrated the glass envelope.  It is my understanding that
stranded leads were used to isolate the vacuum tube, and in particular
its glass-to-metal seal area, from external stress and vibration.

	Incidentally, the glass-to-metal seal area of a vacuum tube
usually uses a glass of different composition than that of the envelope
itself.  Such glass, which is usually borosilicate in nature, is specially
formulated to match the thermal expansion characteristics of the metal
alloys used in the feedthrough.  Such metal alloys are also of special
composition, with two common tradenames being Dumet and Kovar.

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
VOICE: 716/688-1231   {boulder, rutgers, watmath}!ub!kitty!larry
FAX:   716/741-9635                  {utzoo, uunet}!/      \aerion!larry