Re: 15GP22 Rebuild Attempt in France - Soon!

[John Marinello]

Forget about pressurizing ANY crt for ANY reason. Glass is excellent under compression, but should NEVER be subjected to tension. A few pounds into a 15GP22 would cause the ultor flange to act as a bellows, thus ruining that. Add few more pounds, and the tube will explode & cut you to ribbons.

[jeyurkon]

The corrugated crush washer appears to be a different metal than the other parts in the photograph. Is it aluminum by any chance?

John

[TubeType]

Thanks Bob and John.

It was nice to read your detailed explanations of the 15G's construction. I counted five glass-metal or metal-metal junctions. That's ten bound surfaces. This is a mechanical engineer's nightmare.

Have you considered using a large molten glass band to completely encompasses the Ultor ring? This glass band would be fused to front and rear glass surfaces of the 15G. It would include a feed-through connection to the Ultor. If this technique is mechanically sound, wouldn't it eliminate most if not all of the sources for vacuum leaks?

Kind regards,

Terry Cheek

[jr_tech]

Thanks Bob and John for posting the construction details of the 15gp22. Wow! No wonder many of these crts leak. I suspect that percentage wise, more prototype metal cone 15" crts have survived!

I suspect that patching over the outside of the seal areas with frit (or glass) would not be a permanent solution. as flexing of the seal area is likely to fracture these brittle materials. Also, I suspect that pockets of air that could be trapped between the frit and the metal flange could be a source of a "virtual leak" that could over time cause the tube to become gassy even though there may be no detectable path to the outside...

Tough problem !

jr

[ohohyodafarted]

jeyurkon:

The crush washer is of a different metal. I dont have it hear, but it is either aluminum or Stainless steel.



jr_tech:

Your asumptions are right on. We too are concerned about redidual gas entrapment after sealing the metal joints. Hopefully the amount of entraped air would be so minimal as to be absorbed by getter material.

I have a 16gp4 that has milky getters. Presumably from a leak. But it still produces a very good picture. So, it is possible that if the getter flashes are very large, we may be able to counteract the infiltration of any small amounts of gas that might get entraped in the ultor ring after it has been sealed.

Bob

[eberts]

Originally Posted by ohohyodafarted

jeyurkon:
it is possible that if the getter flashes are very large, we may be able to counteract the infiltration of any small amounts of gas that might get entraped in the ultor ring after it has been sealed.

Bob

Nope, the getter only works on a singular molecular level on the surface it is deposited on. Surface area of getter flash is more important than amount of material in getter. You need a good hard vacuum for the tube to work.
Maybe you could rebuild a tube connected to a molecular ion pump continously, then you won't have to worry about a slow leaker.

[jeyurkon]

Originally Posted by eberts

Nope, the getter only works on a singular molecular level on the surface it is deposited on. Surface area of getter flash is more important than amount of material in getter. You need a good hard vacuum for the tube to work.
Maybe you could rebuild a tube connected to a molecular ion pump continously, then you won't have to worry about a slow leaker.

I think Bob did mean "large" in terms of area and not thickness. I believe the getter flash does do better than a single mono-layer, but its pumping speed decreases.

John

[Eric H]

So the problem seems to be sealing the thin metal ring to the thick metal parts.

It has a nice V shaped crevasse that something could be flowed into, seems like Vacuseal should work on something like that unless it can't survive the baking process.
Perhaps if it was a slow enough leak it could be applied after evacuation and cooling were done?

Whatever is used it has to be impenetrable, flexible to some degree, capable of withstanding heat & so on.

I don't imagine there's any way to weld the thin metal to the thick metal without cracking the glass or destroying the seal there.

I knew a guy who could weld aluminum cans together using a Plasma Welder, there's still a lot of heat involved though.