Homemade amplifier with homemade valves

[Syrinx1]

Found this quite interesting....

https://youtu.be/-UEfqAWb3fE

[Syrinx1]

Would it be possible to "repair" valves that had lost vacuum using this technique?

[Bazz4CQJ]

That's a long video and so I've just looked briefly at parts of it. Couldn't find a spot where she mentions what vacuum she's pulling or what kind of pump she has.

I think most basic rotary "Backing" pumps will get you down to 10E-2 Torr (is Torr out of date now?). If you need better, you probably need something more expensive. For glassblowing, I have one of these https://www.ebay.co.uk/itm/172114021...Bk9SR7CC9vKBYQ which will handle borosilicate glass well.

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.

B

[Buzby123]

Well, I'm seriously impressed !.

The amount of hand-crafting that went into just a simple triode.

This must have been how the first valves were produced. But to produce multi-element valves, reliably, and in commercial quantities must have needed huge advances in manufacturing technology.

As to re-vaccing and gettering an old valve, the video gives a clue how it might be done, but it would be a lot of work, and the result would probably not fit where the original did.

[GrimJosef]

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

[greg_simons]

Originally Posted by GrimJosef

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

Looking at glasslinger's videos on tube production he uses getters from old valves that are no good, working on the principle that there's still some unfired material to use, you have to work pretty fast with them once they're exposed to air and become unusable.
Greg.

[JonSnell]

Originally Posted by Syrinx1

Found this quite interesting....

https://youtu.be/-UEfqAWb3fE

You may find this guy interesting.
Shows the theory behind the making of the valve (tube).
https://www.youtube.com/watch?v=GAMRHcbE3g0&t=26s

One could repair a valve that was down to air if the heaters could be replaced and fresh oxide placed on the getter.

[G6Tanuki]

I don't know just how much of a vacuum is needed in a practical valve, but the big silica envelope transmitter valves used in times past were sometimes continually pumped rather than being sealed and gettered.

A modern turbomolecular pump can go down to 1*10^^-8 Pascal, but it isn't cheap to buy or easy to operate.

[Syrinx1]

Originally Posted by JonSnell

You may find this guy interesting.
Shows the theory behind the making of the valve (tube).
https://www.youtube.com/watch?v=GAMRHcbE3g0&t=26s

One could repair a valve that was down to air if the heaters could be replaced and fresh oxide placed on the getter.

Fascinating stuff... I'd love to take a closer look at that lathe!

[Bazz4CQJ]

No doubt, the guy at Brimar will know all about this... but may be coy about disclosing details.

B

[Vintage_RC]

Very interesting video, thanks for posting the link. There are skills and equipment there that I certainly don't have.

[Dekatron]

It’s not a valve but a Nixie but it might anyeay interest you since they are in production with getters: https://www.daliborfarny.com/

[RichardGM]

YouTube happened to offer me this, and I think it deserves a link on here. I'm not sure whether this is the right section, because the project is not mine, but it's as home brew as can be. Mods please move if there's a more appropriate section.
https://www.youtube.com/watch?v=-UEfqAWb3fE

[RichardGM]

I did wonder whether someone had already posted this but couldn't think what to search for.

[FrankB]

I believe the vacuum is most likely a 2 stage mercury pump. We used them in a class for making neon tubes.

(One can't safely repair neon tubes, as they generally inject a tiny ball of mercury into the tube to brighten or change the colors).

John- They do cut open transmitting tubes and replace the filament and cathode, add a new getter and then pump the tube down, reseal them, and flash the getter.
Eimac and Delta do/did this, IIRC. I repaired RF welding machines back in the 70's and we would send the tubes in to either be tested if the owner wanted to know his backup was good, or they could rebuild them.
Note: Never cut or grind the ceramic materialon a ceramic tube as it contains Beryllium in the ceramic which according to mfgr's. inhaling the dust of the ceramic material is deadly.
The process is almost identical to that of rebuilding a CRT, which has been done here for decades.

[peter_scott]

Originally Posted by RichardGM

YouTube happened to offer me this, and I think it deserves a link on here. I'm not sure whether this is the right section, because the project is not mine, but it's as home brew as can be. Mods please move if there's a more appropriate section.
https://www.youtube.com/watch?v=-UEfqAWb3fE

I was interested to see that he just uses a propane torch for his glasswork.

Peter.

[raditechman]

A home made amplifier with home made valves in this video, which shows how the valves were made.

https://www.youtube.com/watch?v=-UEfqAWb3fE

John

[Aitor Eneko]

He makes even the tubes


https://youtu.be/-UEfqAWb3fE