Quote:
Originally Posted by Bazz4CQJ
... I think to try re-vac a valve you'd need an experienced glass blower. The problem will be that the getter has already been fired; that may well be a show stopper 
Bottom line, I don't think it looks viable. |
The lack of a getter would be one issue, although I suppose it might be possible to put more getter material in and re-fire it once the valve is under vacuum again.
More of a problem might be if the valve has an oxide-coated cathode. This is prepared initially by coating the cathode support with a slurry of inorganic metal compounds and then allowing the slurry to dry. The cathode support is then placed in position and the electrode structure assembled. Once the vacuum has been applied the cathode is heated to a very high temperature and the metal compounds undergo a chemical reaction which generates the highly electron-emissive cathode coating. This coating is easily 'poisoned' by even quite a small amount of air. So as well as needing a new getter you'd also need a new cathode and you'd have to go through the hot-chemistry-under-vacuum stage again to create it. It wouldn't be much more trouble to create a whole new valve.
Cheers,
GJ