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What are the most interesting vacuum tubes in your collection?

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radhoo

Tue Mar 01 2011, 09:19PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Here's a rare one, an electrometer tube, used in pH-meters, the 932 Lewis & Kaufman Electrometer:

Primarily invented and designed for the California Citrus industry to determine when the fruit was ready to pick. Juicy!

Proud Mary

Wed Mar 02 2011, 03:42PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

High Power Demountable Micro-Focus Soft X-Ray Source

500eV - 5keV.

Anode end from which beam emerges. Water cooling hoses at right.

Coaxial HV input socket.
Note optical inspection port for gas plasma observation and spectroscopy.

A titanium target is currently held to the ceramic mount, but any desired metal foil can be installed to produce the X-ray spectrum of choice.

Copper water cooling jacket.

Rear View: Micrometer x-y beam alignment controls with view into Grimm discharge hollow cathode.

Rear View: Note high temperature discolouration of metal around alignment hole in hollow cathode assembly.
At bottom right is a plug-in ionization-type vacuum gauge - basically a thermionic diode whose conductance depends on the depth of the vacuum.

plazmatron

Wed Mar 02 2011, 03:51PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Amazing x-ray porn Stella and Anders M!

So heres some more.

A Flash x-ray tube, rated for 150kV pulse, at 60ns duration! Capable of imaging Pylon cables, and through several inches of concrete.

The tube is cold cathode, and is beautifully simple!

Les

Proud Mary

Wed Mar 02 2011, 06:25PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

plazmatron wrote ...

Amazing x-ray porn Stella and Anders M!

So heres some more.

A Flash x-ray tube, rated for 150kV pulse, at 60ns duration! Capable of imaging Pylon cables, and through several inches of concrete.

The tube is cold cathode, and is beautifully simple!

Les

A very elegant device. Is there visible attrition of cathode and anode with frequent use? What are the failure modes of such a tube?

radhoo

Thu Mar 03 2011, 11:51PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

935 from RCA, a Photocell tube:

This old device probably goes back to 1935.

It was used in old movie sound systems, as the reader.

Proud Mary

Fri Mar 04 2011, 12:43AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

radhoo wrote ...

935 from RCA, a Photocell tube:

This old device probably goes back to 1935.

It was used in old movie sound systems, as the reader.

It would be interesting to see how it performs as an X-ray dosimeter. I've just looked at the datasheet here:

You'll see that the peak sensitivity is said to be 3400Ã… i.e. 340nm UV - which is probably the shortest wavelength that can be transmitted through the glass. It may become more sensitive still as wavelengths are shortened into the X-ray region - who can say?

If you wrap the photocell in black artist's paper or black plastic etc and then put 100 - 250V DC (whatever you have available) on the anode, and a 50Î¼A meter in the cathode line, you might see a current flow when you place it close to the 2X2A or your new dental tube. Definitely worth a try!

plazmatron

Fri Mar 04 2011, 01:45PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

Proud Mary wrote ...

A very elegant device. Is there visible attrition of cathode and anode with frequent use? What are the failure modes of such a tube?

The anode tip cannot be seen, it is well hidden in there.

The cathode is made of carbon fibers i believe, and will eventually be damaged by impact from Tungsten atoms from the anode, but it is a slow process.

The anode will end up eroded like any other, however likewise it too is a fairly slow process. The tube warranty is 20,000 shots but MTBF is something like 1x10e6 shots

Les

radhoo

Fri Mar 11 2011, 10:21AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Proud Mary wrote ...

If you wrap the photocell in black artist's paper or black plastic etc and then put 100 - 250V DC (whatever you have available) on the anode, and a 50Î¼A meter in the cathode line, you might see a current flow when you place it close to the 2X2A or your new dental tube. Definitely worth a try!

A good idea, actually this is what I purchased this tube for, I also have some other photosensitive tubes that I will try.

Another thyrathron tube, the 309CE FG-17:

It contains mercury, as can easily be seen in the pictures, thin metallic layers deposits on all internals.

Proud Mary

Fri Mar 11 2011, 10:48AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

radhoo wrote ...

A good idea, actually this is what I purchased this tube for, I also have some other photosensitive tubes that I will try.

Another thyrathron tube, the 309CE FG-17:

It contains mercury, as can easily be seen in the pictures, thin metallic layers deposits on all internals.

I was trying to find a paper for you on the conditioning of Hg thyratrons that have been out of service and moved about for some time. I couldn't find anything with a quick search, but think I remember that the thyratron must be set up vertical, and started on very low power, to give the mercury a chance to vapourize and redistribute where it has been splashed all over the inside. If it was mine, I think I'd first heat the glass envelope with a hot air gun.

Mercury vapour thyratrons will only function correctly over a narrow ambient temperature range, so that a steady equilibrium of Hg evaporation and condensation occurs. Outside this temperature range, thermal insulation may be required if it is too cold, or forced air cooling if it is too hot. I see from the General Electric datasheet that your FG17 has an operating temperature range of +40Â°C to +80Â°C, with +40Â°C being recommended.

I've been too busy to do much with the 2X2A project, but hope to get back into it this weekend.

Did you see PoliÅ£ist, Adjectiv yet? I saw it last night, and thought it really very good.

radhoo

Sat Mar 19 2011, 10:05AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Nope didn't see that one, but thanks for the thyratron advise. I've been looking for an oscillator design using a thyratron tube , and found a few topologies using PFNs, but all of them were said to require a Hydrogen thyratron. I had no success in using my Hg or Xe types of thyratrons that I currently have.
Nevertheless, two of them are operational:

The one with a lot of mercury deposit on glass, even if warmed for some considerable time, failed to vaporize all mercury and arced when applying plate voltage.

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