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Driving X-Ray tube with ignition coil.

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zippotix

Thu Nov 13 2014, 01:21PM

Registered Member #5208 Joined: Thu Jun 07 2012, 06:12PM
Location:
Posts: 86

What would be optimal voltage for filament? Some ancient datasheet suggest about 7v iirc, but at this voltage x-rays emmision is really small. I use rewound MOT for filament heating, without rectification.

Don't know what am I doing wrong, I switched iggy coil for flyback at 35-40kv, which should spit out DC, and yeah, x-rays are visible on CCD and GM counter picks it up.
But this goddamned screen won't light up! Of course i'm running this tube in reverse; HV goes to the single end, other way around there is no emission whatsoever.

This picture was taken with 2C2S tube, supposedly weaker in terms of x ray emission than mine, but it not only lights up the screen, it produces a radiograph.
Setup was flyback driven by simple single transistor and resistor circuit plus some mutliplier.
EDIT: This picture is not mine

Wolfram

Thu Nov 13 2014, 02:26PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

zippotix wrote ...

What would be optimal voltage for filament? Some ancient datasheet suggest about 7v iirc, but at this voltage x-rays emmision is really small. I use rewound MOT for filament heating, without rectification.

With too much voltage on the filament, the tube will conduct a lot of current and drag the ignition coil voltage down. You need to adjust the filament voltage to a value where the tube draws a reasonable current without pulling the output voltage too far down. Some experiments with a variable supply should give you an indication of what voltage to use. If you don't have a variable supply, you could also use a big variable resistor in series with the filament, as long as you have one that can handle the current.

zippotix

Fri Nov 14 2014, 02:13PM

Registered Member #5208 Joined: Thu Jun 07 2012, 06:12PM
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Posts: 86

Those rated for 100W cost as much as real x-ray tube, I experimented a bit today, decreased filament voltage to about 2-3v,x-ray emission is constant and visible, but I think that the voltage is too small, since this tube is rated for 55kV. Maybe it needs more than that to produce x-rays of sufficient intensity to light up the screen?

Conundrum

Sat Nov 15 2014, 12:44PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Yeah. Also what I found is that with my experiments putting an Al tape coating on the back of my foil considerably cleaned up the image as it blocked all the low energy (ie useless) X-rays and just let the useful ones through ie >12KeV

EDIT: You are viewing the correct side right? On mine the "flat" side is actually the back ie side to face the X-ray source.
The front looks a bit like photographic paper ie not quite shiny but almost.
Also I have been told that these can sometimes be improved by gentle heating ie in an oven at 60 celsius for a few hours to remove adsorbed moisture.
Explains why an EL screen from a dead air conditioning panel worked as well but an EL panel which had been sitting open to the air didn't work.

A related experiment I intend to commercialize when funds become available is an X-ray imaging device made from EL phosphor coated onto pyrolytic graphite.
I've actually tried a variant of this and using an off-the-shelf B/W CCIR camera CCD was getting quite good images up until the CCD gave out.
memo to self: next time insulate the edge connectors with UV curing glue first!!
said glue also works well for homebrew EL screens and this works with Jeri's EL/LCD hybrid and peeled screens from random offcuts with broken edge connectors.

zippotix

Sat Nov 15 2014, 02:00PM

Registered Member #5208 Joined: Thu Jun 07 2012, 06:12PM
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Posts: 86

Conundrum, as of now I don't need cleaner image, I need ANY image at all ;). I tried different sides, with different angles, under, over the tube. Only thing that remotely lights it up is the filament. I really have no idea what can I do. One thing I noticed, without filament burning the high voltage doesn't flow through the tube. There are some tiny, static like discharges but that is all.

zippotix

Sat Nov 15 2014, 08:46PM

Registered Member #5208 Joined: Thu Jun 07 2012, 06:12PM
Location:
Posts: 86

I have some progress, kind of. Since I don't have proper power supply for ZVS, and rectification of MOT is always messy, I hooked flyback to the trusty old 200W/12v halogen transformer. As previously, no voltage was flowing without the filament heating. But when I turned the filament on, I could see the tube is "glowing" with faint blue halo. It didn't light up intensifying screen, and got really hot. I'll fiddle about with filament voltage, maybe increase it a bit, hope this will help.

Ash Small

Sat Nov 15 2014, 09:08PM

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

zippotix wrote ...

I have some progress, kind of. Since I don't have proper power supply for ZVS, and rectification of MOT is always messy, I hooked flyback to the trusty old 200W/12v halogen transformer. As previously, no voltage was flowing without the filament heating. But when I turned the filament on, I could see the tube is "glowing" with faint blue halo. It didn't light up intensifying screen, and got really hot. I'll fiddle about with filament voltage, maybe increase it a bit, hope this will help.

Conundrum posted this earlier in the thread:

Conundrum wrote ...

General rule, if you can see the tube glowing green or blue in one small spot or in a band around the tube for larger ones then it is emitting potentially dangerous levels of radiation and needs shielding.

Sounds like it could be producing dangerous levels of X rays, but your screen isn't detecting anything

Andy

Sat Nov 15 2014, 09:15PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Posts: 874

There are some tiny, static like discharges but that is all.

The tube sounds like its leaking in atmosphere, electrons in a close to vacuum, shouldn't make any visual spark.

zippotix

Sat Nov 15 2014, 09:24PM

Registered Member #5208 Joined: Thu Jun 07 2012, 06:12PM
Location:
Posts: 86

Ash, there was literally no increase in radiation, my GM counter picked up like, 3 counts?
Andy, when I wrote about those sparks, I ment that when I close the HV to the pin without filament running, then those sparks appear, between HV and a pin, which are outside the tube. I didn't saw any spark inside the tube.

And I think the HV current is too high, I estimate it about 40-50mA. Any way to reduce it ad hoc?

Ash Small

Sat Nov 15 2014, 10:51PM

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

zippotix wrote ...

And I think the HV current is too high, I estimate it about 40-50mA. Any way to reduce it ad hoc?

This might work, shouldn't cost anything:

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