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Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
I am kind of shopping for an x-ray tube right now, since it would be one more thing to try out with my CW and Marx (in progress) generators. I found this tube on ebay which looks very similar to the tubes you guys have.
Is this kind of tube at all useful for flash x-rays, i.e. in field emission mode without heating the cathode? I suppose much higher energy x-rays could be generated that way, but then the shape of the cathode suggests that the tube would require like 1MV to start signifiant field emission.
Also, is the emission area of this kind of tube small enough to give sharp radiographs, or do I have to look for something with a much pointier anode?
Finally, what's the going rate for used x-ray tubes? Is it common to pay more than 50€ for one?
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
That's a Coolidge heated cathode tube, for CW not flash x-rays. A real flash tube is going on ebay right now. It's pretty cheap at the moment. The going rate for heated cathode tubes is generally 65 EUR, but I've seen one sell for as much as 90 EUR before.
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Yup, I have been shopping from this seller "heruursciences" before, and he is excellent to deal with. I am just not sure now what I want, I have the means to power both a CW and a flash tube, so I wonder which is "better", or more interesting. I suppose I would end up paying about the same for the two tubes, and I am definitely not prepared to buy both at this point.
Do you (Uzzors) have one of those flash x-ray tubes, or are you "abusing" some other tube for that duty? Was was wondering that if rectifier tubes can be used for flash (and also CW, right?) x-ray, than maybe a CW x-ray tube can also serve as a flash tube in a pinch?
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
HFsstc-freak wrote ...
I cut up a modern flyback once, it had the hv winding wound as a standard transformer.
Wtf?
Joe, in my experiments I'm abusing a 2X2-A HV rectifier. It seems to be producing good amounts of x-rays while driven in flash mode, though I wouldn't try it in CW. The power dissipation capability of the tube is so low, and the CW radiation wouldn't be very impressive. People have used normal tubes in CW mode, but they require long exposure times and have low penetration. I don't think Coolidge tubes will work too well as flash tubes, since they have such a hard vacuum. I'm not sure about that though. It's best to use the tubes as they were designed to be used.
Registered Member #941
Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497
Well the flyback was shot after i overpowered it with a mazzilli driver, and i wanned the core, so i took a hacksaw and just cut it lenghtwise a number of times until the core was free.
Before that i chiseled up another modern flyback to keep the windings intact, both had the hv winding wound like a standard transformer, not in sections like the x-rayed one.
You sure its not just the lv windings we see ? Those attached to the pins.
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
I`m with Uzzors on this one, if you are going to buy a coolidge tube, you might as well build a proper PSU for it. Judging from the tube, it is well used, and overvolting it like this would probably damage it. Ordinary cooolidge tubes, WILL begin to flash over internally towards end of life anyway, and thats at their design voltage.
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Home made x-ray machine.
