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Rebuilding an x-ray tube.

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LAN_403

plazmatron

Fri Apr 06 2012, 08:59PM

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

Yes, I would consider the targets more or less consumable in a situation like that. I don't think metal vapors would make it to the pump down the bellows hose, but the inlet valve to the diffusion pump is protected from debris by a metal screen. Condensing metal would undoubtedly foul up the tube, but all that would entail is a periodic cleaning job, so no problem with this!

I'm still using the Javac, I just happened to call it a "refrigeration service pump" since that is what it is, and to differentiate it from its larger cousins. Its an excellent little pump! I think I mentioned a while back I am now running it on "Diffoil" which can allegedly be used in diffusion pumps too.
It will just about pull an x-ray vacuum all by itself....

The diffusion pump is different from the last one I described on here, and was another fleabay special that someone found in a skip somewhere! Took about 2 weeks to remove all the rust and grot off the thing! But its nice and small with standard flanges, and stands a little over 7 inches tall.

Yes I have seen some of those tubes, and even considered buying one for a while, but unfortunately the cabinet, and cooling system had already been built around the tubes I had, and would be a real pain to redesign.

I Just ordered my elbow fittings, so hopefully I can re install this thing in its cabinet, and get cracking again!

Proud Mary

Fri Apr 06 2012, 09:28PM

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

I bought a BSM1-Ni three or four years ago, and as you can see, the window sealant looks past its best, but I have fired it up half a dozen times or so, and found it to be in working order.

I look forward to hearing more of your experiments with the demountable source, as you are the only experimenter I know, besides myself, who has one.

plazmatron

Sat Apr 07 2012, 02:17PM

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

That's the model of tube I was looking at on fleabay. Yes, the window looks a little corroded there, but if it works, it works!
Better than some of the rusting hulks I have seen!

Hopefully when the remaining plumbing shows up, and it is reinstalled in its cabinet, I can crank it up to full power and take some decent radiographs with it.

Initially, the point of this creation, was to re-manufacture the tube, and have it up and running to its original specification. However, the possibility of using other anode materials, and other cathode designs, makes this an interesting experimental platform, as well as a workhorse for radiography.

Whilst waiting for the parts to appear on fleabay to complete this project, I have also built a variety of parts onto vacuum flanges, including a linear positioner. This was built using the stainless bellows from an old vacuum valve, and allows me to reposition targets or cathodes etc, on a live pumped down system.
The impetus for that particular creation was for further experimentation with unheated carbon fiber cathodes. They can work well under certain circumstances, but do require specific distances at different voltages to function properly.....

Linas

Sat Apr 07 2012, 04:08PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

here is mine diffraction tubes :)

Proud Mary

Sat Apr 07 2012, 04:53PM

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

I see that while I was taking a quick snap of the 0.0045BSM-1-Ni window corrosion for Les's diagnostic opinion, Linas has posted up a picture which shows similar deterioration of the windows. I wonder if this damage can be made good in some way before it compromises the integrity of the vacuum seal.

Les, your new series of experiments sounds very exciting and creative: the target positioning device will be quite a tour de force!

Ash Small

Sun Apr 08 2012, 01:29AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

plazmatron wrote ...

Hopefully when the remaining plumbing shows up, and it is reinstalled in its cabinet, I can crank it up to full power and take some decent radiographs with it.

What plumbing do you need, Les? I may be able to help out.

This is a very interesting project, I'm toying with a similar idea myself, but not for X rays, just a high power valve (VT).

plazmatron

Sun Apr 08 2012, 02:05PM

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

Proud Mary wrote ...

I see that while I was taking a quick snap of the 0.0045BSM-1-Ni window corrosion for Les's diagnostic opinion, Linas has posted up a picture which shows similar deterioration of the windows. I wonder if this damage can be made good in some way before it compromises the integrity of the vacuum seal.

Les, your new series of experiments sounds very exciting and creative: the target positioning device will be quite a tour de force!

That doesn't actually look too bad. Certainly not like mine were. There were visible pits in the coating on mine, and even more so after use. It is evident on yours that they polish or wirebrush the Be surface after installation, so it is likely that manufacturing techniques had changed over time.

The only suitable coating I can think of is Vacseal, however, it should be noted it can take weeks to dry, and may in fact dissolve the coating that is already present.

Yes, there are all sorts of things that can be made possible my manipulating internal vacuum components. I was also thinking about having a stepper motor in a tube, driving a disk with a selection of targets on the edge.....

Ash Small wrote ...

What plumbing do you need, Les? I may be able to help out.

This is a very interesting project, I'm toying with a similar idea myself, but not for X rays, just a high power valve (VT).

Thanks Ash, but the parts are ordered, and will likely turn up after Easter.

A high power valve, like a transmitting triode?

] mouromtseff_et_al_1944_review_of_demountable_vs_se aled-off_power_tubes.pdf[/file]

Planning on building a 300kW VTTC ?

Proud Mary

Sun Apr 08 2012, 02:50PM

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

plazmatron wrote ...

Yes, there are all sorts of things that can be made possible my manipulating internal vacuum components. I was also thinking about having a stepper motor in a tube, driving a disk with a selection of targets on the edge.....

The bellows/concertina mechanism from a vacuum variable capacitor could be used to vary the distance between anode and cathode.

IntraWinding

Sun Apr 08 2012, 03:06PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

Proud Mary wrote ...
I wonder if this damage can be made good in some way before it compromises the integrity of the vacuum seal.

Electroplating?

plazmatron

Sun Apr 08 2012, 03:22PM

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

Proud Mary wrote ...

The bellows/concertina mechanism from a vacuum variable capacitor could be used to vary the distance between anode and cathode.

I had considered that, but I have been short of money due to exams, so I used the internals of an old bellows sealed vacuum valve I got in a junk box of parts I bought of fleabay.

It all worked out quite well. The flange the base of the bellows, was just the right size to silver solder an NW-40 O-ring carrier to. I have yet to make an actuator for it, I was thinking of something involving a micrometer head.
I have a smaller bellows out of a burnt out NW-10 valve too. There is less 'reach' to it but will be much more suitable for smaller tubes.

I am pretty keen to try out carbon fiber cathodes with this, as they really do seem like a promising alternative to heated cathodes for tiny tubes!

IntraWinding wrote ...

Electroplating?

Probably not. Beryllium forms a hard Beryllium oxide passivation layer. The oxide is normally very stable unlike other metal oxides, in that it does not spall off, like rust, but forms a durable barrier.

Coating with other metals would interfere with the characteristic x-ray emission, by attenuating various lines too.

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