Rich Measures wrote:
> RF Parts sells graphite-anode 3-500s at a reasonable price. Heating
>causes a graphite anode to release stored gas.
That's like saying "heating causes your house to burn down".
Heating causes *all* tube materials to release stored gas, if the
temperature is high enough. That's why they are heated during
manufacture to very high temperatures - far higher than the anode or
grids will ever reach again - while still being pumped.
After the tube is sealed, outgassing continues very slowly throughout
the life of the tube, at a rate depending on the purity and cleanness of
the original materials.
At normal operating temperatures, graphite is a very efficient absorber
of gas. It can also be coated with other getter materials such as
zirconium. These getters operate more effectively at higher temperatures
(within the normal range).
For more information about this topic, follow John Lyles' advice and get
hold of W H Kohl's "Handbook of Materials and Techniques for Vacuum
Devices", American Institute of Physics reprint, 1995, ISBN
1-56396-387-6. It's already out of print, but I obtained a copy here in
the UK on inter-library loan.
It contains more than you ever want to know on the subject, but it
really is about vacuum technology/physics viewpoint and not specifically
about transmitting tubes. However, it does contain whole chapters on
'Graphite' and on 'Getters'.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|