CRT decay - test-drb@ccmp.vtda.org

2 Nov 1998

______________________________ Reply Separator _________________________________
Subject: Re: CRT decay
Author:  classiccmp(a)u.washington.edu at internet
Date:    11/2/98 12:00 PM

 At 11:41 AM 11/2/98 -0500, Marty wrote: 
...

 Sounds like you may be talking about a 'getter' which is used in the 
 production of vacuum tubes (valves for you gents across the pond) to
 eliminate vapor and residual air the vacuum pump can't draw out or may 
 be in the metal components of the tube (plate, grid, filiment and
 arbor). The getter is a compound (barium, magnesium, etc.) placed in 
 the tube which is ignited after the envelope is sealed. After the
 getter ignites it sometimes leaves a silver coating inside the tube.  
 Yes, "getter" is the word.  The substance I remember would generate 
 an ozone-smelling gas when wetted.  It physically resembled calcium 
 carbide in color in appearance.

...
 >Offhand, I'm not sure how this coincides with
your description of an 
>ignited compound: you'd think there wouldn't be much oxygen there
>at that point in manufacturing, and what combustive process would 
>*release* free metal?  
 From what I've read there are traces of oxygen actually in the metal 
 parts, plus the vacuum pumps cannot draw all residual gas from the 
 tube. The getter flashes and literally burns the residual gases from 
 within the tube and the metal components. A byproduct is the 
 silvering on the inside of the tube. I can look up the process and 
 give you more details if you wish. I have a 1935 book entitled 
 'Theory of Vacuum Tubes in Radio' which goes into great detail on the 
 matter. It explains the various getters and why they were introduced 
 in manufacture along with the chemical makeup of the getters. 

 Marty

 - John

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 &lt;classiccmp(a)u.washington.edu&gt;
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