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Vacuum Rectifiers X-rays report

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uzzors2k

Tue May 17 2011, 07:13PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

I'm a bit late to the party, but this past weekend I was finally able to do some 2X2A experiments of my own. Several years ago (2007) I purchased some American 2X2A tubes for this exact purpose, but seeing Leslie's page on flash x-rays convinced me to try that instead. One weak Marx generator and no x-ray images later I shelfed the project, until seeing Radu's thread here.

Some quick tests showed that a surprising amount of x-rays were generated, and even with great shielding (~3cm of transformer steel) enough was scattered to register on my Geiger counter at three meters distance. Our bathroom is lined with ceramic tile and on the ground floor, so it seemed an ideal place to run the experiments from here on. Since I still live my parents

I needed to make the setup quick to deploy, otherwise I'd never get it setup while they were away. This involved fitting an ammeter, high voltage source, tube mount and shield in the same location. The high voltage source was constructed specifically for this purpose, and consists of two rectified flyback transformers in series driven by a current-mode controller. Voltage can be set from 0-50kV. The transformers are sealed in a PP pipe filled with motor oil. To keep myself safer, I've constructed a fiber optic timer unit and relay, so the exposures can be controlled from a distance. The 2X2A itself is also sealed in oil and wrapped in tin foil to suppress inadvertent lighting of the screen. This also serves to protect the tube itself from arc-overs.

Some tests with the tube showed that unlike the Russian model, the American produces the most x-rays while driven in regular polarity, with the anode at HV. Turning my high voltage supply to max, the voltage across the tube was measured to be 42kV, at 210ÂµA. I took some images of the internal structure to see if any points of localized heating showed up, but nothing stuck out. Due to my camera's built in timer limitations I was only able to run the tube for a few seconds before the picture was taken.

Like Radu discovered however, the American model is far inferior to the Russian in terms of radiation output. I was barely able to x-ray an IC, even with 30s exposure time and digital enhancement. Still, it did work, which is pretty neat considering the basic components used.

Patrick

Tue May 17 2011, 09:58PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Uzzors wrote ...

.... the American model is far inferior to the Russian in terms of radiation output....

Not to put my huevos out, but when you say the American version is inferior to the Russian one, what do you mean?

When used as intended is lower radiation more desirable? You all use these device for an off-label purpose so I have no doubt the Russian one is better for more X-rays, but most makers probably try to avoid excessive radiation?

Putin cant start car....

uzzors2k

Wed May 18 2011, 07:55AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Haha, I had a feeling some patriot would feel his feathers ruffled from line. To clarify, which I can do using just the segment you've quoted: the American model produces less radiation than the Russian model, which in this application is undesirable, and thus inferior. On the contrary, the American model is superior in terms of tube characteristics (I assume), shock tolerance and aesthetics, but that's of no concern to me in this project.

You've labeled me as a commie now haven't you.

Patrick

Wed May 18 2011, 02:37PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Uzzors wrote ...

Haha, I had a feeling some patriot would feel his feathers ruffled from line. To clarify, which I can do using just the segment you've quoted: the American model produces less radiation than the Russian model, which in this application is undesirable, and thus inferior. On the contrary, the American model is superior in terms of tube characteristics (I assume), shock tolerance and aesthetics, but that's of no concern to me in this project.

I was being Facetiuos with the "huevos"commemt, but thats what I thought your were meaning, about the American version.

Uzzors wrote ...

You've labeled me as a commie now haven't you.

Not yet.

radhoo

Tue May 31 2011, 03:48PM

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

Hi Eirik,

It's great that you're using your DSLR for these photos, it brings some serious enhancement to captured images quality, I only wish you did more of those. Are you planning to try your setup with other vacuum tubes as well?

Nah

Tue May 31 2011, 07:29PM

Registered Member #3567 Joined: Mon Jan 03 2011, 10:49PM
Location: USA, 1960s
Posts: 260

I would suggest some of the early diodes in tvs, i'm talking from the 30's.

radhoo

Thu May 16 2013, 12:16PM

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

Russian GP-5 vs Russian 2x2
I remember Linas mentioning the GP-5 tube. Indeed it looks like a good candidate for the purpose of this topic, given its size and solid construction:

It does produce x-rays when energized at 50KV in reverse polarity, but nothing compared to the 2X2. Here are some images:

GP-5 in normal polarization (+50KV to anode)

The first two pictures are original, as recorded by the camera.
The third picture was enhanced in software with a Gamma Correction factor of 3 (increased exposure/luminosity)
The forth shows the same setup, but having a Kodak intensifier paper cylinder wrapped around the tube. Software enhancement, with the same gamma factor of 3. No green fluorescence can be observed.
Exposure settings are: 2nd picture: 10s/F5.6/ISO 500 and for the 4th picture: 13s/F5.6/ISO 800

GP-5 in inverse polarization (+50KV to the cathode)

2nd picture is a gamma corrected variant of the first, factor of 3. 1st picture settings: 13s/F5.6/ISO 800

Here is the tube with the Kodak intensifier screen:

2nd picture is a gamma corrected variant of the first, factor of 3. 1st picture settings: 15s/F5.3/ISO 640
Some green fluorescence is visible.

And here is the 2X2 tube, place instead of the GP-5, in the same exact setup:

2nd picture is a gamma corrected variant of the first, factor of 3. 1st picture settings: 15s/F5.3/ISO 640
Increased amounts of radiation are being produced.

Conclusion: at 50KV, the GP-5 produces some x-ray emissions, but nothing compared to the 2X2.

2X2 energized at 50KV in reverse polarity
See the impact zones on the heat shield and glass.

Proud Mary

Thu May 16 2013, 01:07PM

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

Interesting experiments, Radhu, but the results are no surprise.

Let us think about the basic differences between 2X2 and GP-5.

2X2 was designed as a high voltage rectifier diode during the Second World War. It was designed to rectify RMS max 5.5 kV, and 12.5 kV PIV. This means that when operated within its design range, the soft X-rays produced by electron bombardment would be completely stopped by the glass envelope, so no X-ray shielding was included in the design.

By contrast, the Svetlana GP-5 was designed as an EHT shunt stabiliser triode for colour television service. Its maximum anode working voltage was 30 kV, so effective X-ray shielding has been built into the design, as we see clearly in your pictures. The envelope glass very probably contains lead or other heavy elements to attenuate radiation leaking round the shield. As colour TV broadcasting did not start in the former Soviet Union until 1967, I would judge this valve to have been designed after the significant X-ray hazard of earlier American EHT stabiliser triodes like 6BK4 (1955) was well known. So your experiments have proved the superiority of Soviet engineering! :)

Stella

radhoo

Thu May 16 2013, 01:19PM

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

Thanks for the adding these details. Indeed the GP-5 seems to come with lead glass, as the tubes feel so heavy.

Proud Mary

Thu May 16 2013, 08:10PM

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

radhoo wrote ...

Thanks for the adding these details. Indeed the GP-5 seems to come with lead glass, as the tubes feel so heavy.

I have sometimes wondered - and I am sure you will have thought of this too - how much the application of an external magnetic field might be able to increase the output energy by a partial 'cyclotron effect.' Even if it added only a short extra distance to the electron path, it might increase the output energy considerably.
Success is most likely to come by choosing a high voltage valve with the most favourable electrode architecture, one where at least part of the electron path would not be shielded from the magnetic field by, for example, the anode.

What do you think?

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