"Harry Conover" wrote in message
...
The ultimate level of vacuum in the tube is produced by "gettering"
once the tube has been sealed. Gettering involves the vacuum
deposition of a special metal film ...

Typically barium, AFAIK.

I hope this sheds some light on what is now an increasingly extinct
technology except for .. extreme audio enthusiasts,

Hello
http://webpages.charter.net/dawill/Images/6W6_PP.jpg

and survivalist radio operators. :-)

- Soon to be, with any luck...

Tim

--
In the immortal words of Ned Flanders: "No foot longs!"
Website @ http://webpages.charter.net/dawill/tmoranwms