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EEYORE

Wed Dec 23 2009, 03:35AM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Hello,
Thank you for the very informative post! I will get to sit back and think about things a bit more since I lost the auction.

Maybe the seller will give me a buy it now price for another. (He claims to have more). Dual HV power supplies seems to be a bit more complex than I wanted to go with. Is that for all xray tubes, or just the type I had posted? Maybe I ought to look into a different kind of xray tube?

Matt

LutzH

Wed Dec 23 2009, 09:36AM

Registered Member #1721 Joined: Sat Sept 27 2008, 08:44PM
Location:
Posts: 136

Hello:

Hey don't sweat it, the tube you missed is about as generic as they come. Far better is a tube with a smaller focal spot which equals higher resolution. Mammography tubes are great for detail work, plus they usually have a grounded anode so the HV power supply is much simpler. This said you do not really need dual power supplies, you can just use dual voltage multipliers with the same HV source. Just make one for +, and one for - potential. This also makes winding your own HF tranny easy because you have two HV coils which offer far lower stress. For me the low energy x-rays are the most interesting, but you have to use film, or screen shots for imaging because the glass front of the intensifier tube absorbs them.

Do not be afraid of using a big ass tube, the big medical tubes work great, plus they are well shielded to boot. When you run them at under 10-20 ma you do not need to spin the anode at all. They may be bulky, but they have 1.2 and .6mm focal spots so you even have a spare filament built in. Learn on the large one, and if you blow it (which is unlikely) then you have the good one as the spare. This is what I used for fluoro, I could run it all day at 5-10ma. I also used it to irradiate my veggi garden seeds, and some seeds for a friend many, many, years ago. My results were not that unusual just some minor mutations, and crooked pole beans, but my friend had a purple colored cannabis plant which looked so unusual that it could be grown to maturity right in his front yard, on a busy Seattle street. Sadly he did not let it seed or maybe he would be retired right now :) I never liked the effect so I could care less, it just made me go to the hardware store an buy a bunch of useless stuff. All the while thinking that I was going to make some profound and complex thing, like an X-ray tube from the parts, ya right.

The medical tubes are the way to go unless you find a micro-focus tube on ebay. Also nobody wants them so you can get them for cheap, they do have to be packed very well for shipping, which is the only drawback. Connecting them to HV is easy to, if you ground one end you can go up to 70KV on these with no problem because medical tubes are rated at 120 or 150KV. They have really good built in shielding as I pointed out before, so you only need to shield downwind of the X-ray port at 60-70KV. Plus they can crank out the ma! I got enough x-ray emission from one to light a screen near the port with just a rectified 15KV NST!!! Put a doubler on this for about 40KV and you can fluoro ok with the unit you were considering. If you spin the anode with a motor start cap, then you can use a HV capacitor and do short exposures of like 1/30 sec to x-ray a live mouse with no blurring.

Take Care....Lutz :)

EEYORE

Wed Dec 23 2009, 07:50PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

What I liked about that tube was that it was cheap and small.

I like to ease into new areas before going all out. I started lasers with little red diodes and now play with 40W IR laser diodes.

High voltage started with piezo clickers and then turned into full blown 1kW DRSSTC stuff. (Thats as big as I could afford).
Radioactivity started with autunite and now is multi-pound pieces of pure uraninite! (80-100mR/Hr of gamma).
I got my feet wet with the mini-focus tubes sold by plazmatron, but want to ease into things more considering this is the most dangerous thing I have done.

Matt

Proud Mary

Thu Dec 24 2009, 10:53AM

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

LutzH wrote ...

medical tubes are rated at 120 or 150KV.

Aren't mammography tubes with Mo-Mo target/filter combinations generally run at 25-27kVp or so?

EEYORE

Thu Dec 24 2009, 08:18PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Hello,
So I won this tube:

Its lower voltage, but so tiny!
I can build a dual +30kV/-30kV with two tv triplers, no?
Does this tube look good? There is a larger one, but $90.00 just seemed like alot for a used item with no guarantee, plus I dont feel like having to build two 45kV PS to power it.
Did I do good? Or did I do bad?
Matt

LutzH

Thu Dec 24 2009, 08:55PM

Registered Member #1721 Joined: Sat Sept 27 2008, 08:44PM
Location:
Posts: 136

Hello:

Since it is so small, just plop it in oil, and you can use just one + HV source on the anode end and leave the cathode end grounded. If you use a short section of clear PVC pipe, you can buy rubber endcaps for this diameter tubing in the plumbing section of the HWStore. These will allow for any expansion of the oil, real simple. In this case the small size works in your favor :) You can then mount this PVC tube in a larger PVC T fitting wrapped in lead, for an easy build.

This tube will do from 2-10ma depending on the design. If you run it at under .5ma and under it will last a long, long time. Looks like you are in bussiness :) For radiography 1 ma is just fine, just watch the temp in long exposures, oil again helps here a lot.

I would use it at 30-60KV depending on what you are doing. A flyback with a simple VM works great, you can even use a HF NST as a super simple HV source for a FWVM. For diodes I would recommend 2CL2FM 20KV 100-200ma ones. These are great for VM's <100nS to boot, best cost vs performance ratio of all the diodes I have seen on ebay etc.

Reference anode material W is better than Mo for general use. Mo is great for small stuff, due to its nearly monochromatic 19KV emission with a Mo filter. For real small stuff W is better again due to its 6-8KV L peak.

Take Care.....Lutz :)

EEYORE

Thu Dec 24 2009, 09:43PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Hello,
So I did good.

So now I need to find some HV oil. Any tips on getting a small quantity of oil?

Also, instead of building a 60kV VM, might it be easier to just make a +30kV/-30kV supply with one beefy flyback and two TV triplers? Am I correct in thinking that I can run one tripler in reverse to get -30kV out and then connect that to the cathode? Then the other tripler would be run for +30kV and connected to the anode. Or, do I have myself confused? If this would work as well as a straight +60kV VM, then it would be much much cheaper! (TV triplers are $15.00 on ebay).

I won two Resonance Research flybacks. They ought be plenty for this. I will drive them (Or one) with my 105W Halogen Light electronic PSU. Maybe I ought to use battery power for the filament?

I will plan to run the tube at 1mA max.
Thanks!

Matt

Proud Mary

Thu Dec 24 2009, 10:40PM

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

Your tube has seen a fair bit of use - notice the discolouration of condensed anode material on the inside of the glass.

Any tube which has been out of use for a month of so must be seasoned before the full voltage is applied to it. Seasoning consists of an incremental increase of kVp until the full working voltage is applied, and serves to reabsorb gases that have built up in the tube.

If your kVp max is, say, 75kV, then you might run it for two one minute periods at 20kV with one minute between them. You would then repeat this process at 25kV, 30kv and so on.

It is important that the filament or heater should be thoroughly warmed up before any EHT is applied to the tube. Check heater continuity with a multimeter as soon as you receive it.

EEYORE

Fri Dec 25 2009, 06:58AM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Uh oh...So how long might it have left? I hope long enough for me to get bored with it.

I will season it as you say. Does my reasoning (with regard) to the EHT supply sound reasonible? I may go ahead and get a second tripler to make a negative 30kV power supply.
EDIT: Might the other tube he is selling be a better investment? Here it is:

Matt
Merry Xmas!

Proud Mary

Fri Dec 25 2009, 10:48AM

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

EEYORE wrote ...

Uh oh...So how long might it have left?

Who can say? The reasons for taking a tube out of service include filament/heater failure, arcing, reduced emission, glass electrolysis, crazing of the anode material deposited by condensation on the glass, and excessive field emission, such that the tube cannot be fully controlled by altering filament or heater current.

I hasten to add that I have no personal experience of such powerful tubes as yours, nor of using second-hand tubes, and suggest you ask Plazmatron for his opinion.

EEYORE wrote ...

I will season it as you say. Does my reasoning (with regard) to the EHT supply sound reasonible? I may go ahead and get a second tripler to make a negative 30kV power supply.

If you adopt this approach, you will have to have the filament supply 'floating' with respect to the ground, and with the ability to stand off 30kV. I use Enersys Cyclon rechargeable lead-acid cells for this purpose because of their superior energy density. The 2V 8AH Cyclon cell
is little bigger than a "D"cell. If you operate your tube with EHT+ve on the anode, and the filament-kathode at earth potential, then you can run the filament 'heater from an ordinary transformer.

EEYORE wrote ...

EDIT: Might the other tube he is selling be a better investment?

Who can say, Matt? I note that your seller's email address is xrayrepair and that he doesn't accept returns. I wouldn't buy it myself, because I'm in no doubt about the difficulty and cost of building a safe, stable, and reliable power supply of 90kV on the one hand, and the costs and labour of providing sufficient shielding for such energetic photons.

From a personal perspective, I prefer table-top experiments, rather than something that would soon take over an entire room.

A Merry Christmas to you, Matt.

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