[AMPS] gettering

[Tom Rauch]

> >//   Where is the getter in a 3-500Z?
> >Where is the getter in an 8877?
> >Can gettering take place while a tube is cold?

This has been covered a dozen times on this reflector.

The 3-500 gettering agent is zirconium, the gray powder-looking 
coating on the anode. It is sprayed on, and activates at about 1000 
degrees C. In the ideal case it should run at various temperatures, 
because the gas liberated at one temperature is absorbed at 
another. 

The 8877 uses tantalum. It is mounted near the cathode and 
heated to temperature by the heater.  This was one source of 
chronic 8877 failures in the 80's, because the cathode was moving 
when the tantalum was warping.

All getters outgas to some extent, as do other  elements in the 
tube.

Arcs also getter the tubes, by causing a plasma that breaks-down 
the gas into harmless elements that bond to material in the tube. 
As a matter of fact, some tubes are (or used to be) gettered during 
manufacture with intentional internal arcs. 
 
> I recommend contacting the manufacturer for these questions. If you
> prefer to avoid Eimac, then talk to Claude Peterson at Econco in
> Woodland, CA. (800) 532 6626. He was involved with some of the glass
> Eimac tubes at Salt Lake City before they sold that operation. Maybe
> the 3CX1500A7/8877 as well.... Let us all know what you find out.

Why depend on someone else to accurately convey what is told? 

Rather than take second-hand info, you can find books on the 
subject. There are entire chapters on gettering.

Try the Electronic Designers Handbook and other detailed 
engineering books. Eimac mailed me 19 pages of information in 
1982 titled "Getters and Their Function in Vacuum Tube 
Manufacture".

They also mailed info on neutralizing grounded grid tubes. Rich 
may have copies of both that he hasn't read yet. 
73, Tom W8JI
W8JI@contesting.com 

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