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Registered Member #2119
Joined: Mon May 11 2009, 04:30PM
Location:
Posts: 15
Regarding not using it at full rating: I'm not going to use it at all until I can find a decent oil and vacuum down the enclosure like you all suggest.
But, then again, maybe I should at least test it with a quarter of its rated voltage or something... I don't even know if it's good or not. It doesn't look damaged or burned anywhere, but who knows... Could be internally damaged or something.
I've got a nice variac I could throw it on. Dial it down to like 40 volts or something and see what kind of output I get.
Registered Member #1721
Joined: Sat Sept 27 2008, 08:44PM
Location:
Posts: 136
Hello:
Just in case you have not already figured it out, there are 2 seperate filament transformers, each may have a ground also, here is what I would do overall:
1. The largest input wires should be the HV Primary, the HV secondary has a centertaped grounded winding, you must ensure it is grounded, they have these centertap wires come out of the core for current monitoring, so these could be 2 of your smaller wires which you absolutly need to ground.
2. Run 12V AC into the primary, at this voltage you should get about 6-12KV output, and it will handle this without being in any oil, now you can test, wire and refine everything at this level.
3. Drop it in oil in a big pressure cooker, pull a vacuum for a while, a bucket will colapse from the vacuum, I tried it!
Registered Member #2119
Joined: Mon May 11 2009, 04:30PM
Location:
Posts: 15
That does help.
I thought that the high voltage secondary was probably grounded to the iron core. There's a small wire that is coming out from underneath the two large bobbins, and it appears to be inserted between two of the laminations upon exiting from under the bobbins. So, I suspect the two clear-cased wires are the HV out, and the small wire going out from under the bobbins is the grounded center tap.
The five input wires (which I'm surprised are not of a larger gauge than they are)... Three are probably 16 gauge or so, the other two are probably 18 gauge or so. I would guess that the three larger ones are the primary wires. Maybe two are power input, and one is the ground for the current meter? The two smaller ones... I'm not sure what they are for... I would think filament, but then why was there a separate transformer in the unit? I thought it was for the filament....
Hmmm...
Regarding the bucket collapsing... Good point! I will try the method you mentioned.
I'll also try the 12VAC test method since it doesn't require oil submersion for testing.
Thank you for all the input! Your suggestions and thoughts are very much appreciated.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
You can identify the HV return wires by measuring resistance from the HV outputs to all of the wires coming from the bottom of the windings. If you have manual range DMM, you might need to set the resistance quite high.
Registered Member #1500
Joined: Sat May 24 2008, 04:38PM
Location: Ojai, Ca.
Posts: 44
Regarding Scintillation counters. I used to work for a radioactive measurement company near Argonne National Lab. We used a very heavy lead pigs and loaded a radium pellet as a standard.
On either end of the pig were two photo mutiplier tubes that never saw any natural light from the day of manufacture. A vial with a prepared scintillation fluid along with the samples were automatically loaded via an elevator and the flashes were counted for hours or years with shift registers (alot of 74xx chips!) and nixie tubes for readout. Printout was via a teletypewriter;-)) Safety was not so good in those days as someone accidently sucked up a radium pellet. I had a fair amount of tritium in touluene burst under presure in my face (no saftey glasses). I was bandaged for two weeks and no one or doctors knew if I would be able to see again as it was somewhat unprecedented. Yikes. So osha ain't so bad.
Registered Member #2119
Joined: Mon May 11 2009, 04:30PM
Location:
Posts: 15
Everyone,
I finally got around to testing the transformer and the x-ray tube. Both appear to be in usable condition...
Transformer: The three thicker leads are indeed a center tapped primary. The green and brown are the full winding, while the red is the center tap. The two smaller brown leads are associated with the high voltage winding in some way. Probably monitoring taps for the metering equipment as someone else mentioned. The two clear leads on top are of course the ends of the high voltage winding, center tapped/grounded to the laminations. I grabbed a variac and started ramping up the voltage. At roughly 10VAC I could hear ionization of the surrounding air. Brought it up to about 12-13VAC and got an arc from both ends of the HV winding to the core, and an arc from clear lead to clear lead about double the length of the leads to core. I didn't raise the voltage anywhere past 13VAC or so because the transformer isn't under oil. Don't want to fry the poor thing. But, it appears to be in decent shape. BTW, the resistance reading from clear lead to clear lead was very high. As in, my DMM didn't read any continuity. I thought the winding was open and figured it was dead, but upon applying voltage, I got good arcs from both ends of the HV windings so I guess my DMM was just unable to read that high... Hmmm..
x-ray tube: I tested continuity between the three terminals on the filament side. The two outside lugs read about 0.9 ohms and each outside lug to the center lug read about 0.45 ohms. I then used an AA battery to test the filament and nothing. So I grabbed my variac and brought it up to 3.0VAC. When applied to the two outside lugs, the full filament began glowing. I dropped the variac down to about 2.0VAC and tested each of the outside lugs to the center lug. This produced glowing in one half of the filament, then the other half. Looks like the medical unit had two settings for x-ray strength/hardness.
Sooooo... It looks like I have some fun parts to work with. I would guess (although I did not test the diodes or filament transformer) that the unit was discarded for some other failure besides the x-ray head. Maybe the x-ray image intensifier tube? That looks like an expensive part! Reminds me of part of the 'project' from of the movie "The Manhattan Project" or something.
Thank you all for your advice on testing the transformer.
Thanks, Brad
P.S. - Also thanks for the story about the scintillation counter. Sounds like a bit of a health nightmare at times, though! I just want to get a few of those tritium light sources for my keychain. The USA doesn't like us peasants having tritium light sources laying around. Let alone a bottle of tritium/acetone. Heh.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
BradStockdale wrote ...
x-ray tube: I tested continuity between the three terminals on the filament side. The two outside lugs read about 0.9 ohms and each outside lug to the center lug read about 0.45 ohms. I then used an AA battery to test the filament and nothing. So I grabbed my variac and brought it up to 3.0VAC. When applied to the two outside lugs, the full filament began glowing. I dropped the variac down to about 2.0VAC and tested each of the outside lugs to the center lug. This produced glowing in one half of the filament, then the other half. Looks like the medical unit had two settings for x-ray strength/hardness.
Rotating anode X-ray tubes usually have two filaments for broad and narrow focus. One side of each filament is connected to the focusing cup, which thus forms the point of common connection between the HT and LT circuits at the cathode end of the tube - which is why you have three wires.
Registered Member #2119
Joined: Mon May 11 2009, 04:30PM
Location:
Posts: 15
This tube is a stationary anode type. There's images posted in my first thread about the unit...
About half way through the thread there's several images posted of the whole unit, and the initial images of the x ray head when I cut it open, including several shots of the tube alone.
I do have a rotating anode type tube as well that appears to be in working order. It too has double filaments.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
So far as I can make out, the tube is now obsolete, and is available only as re-manufactured units from German Electric.
Whether the anode be rotary or stationary, the purpose of the twin filament system is to provide (a) fine focus with small spot size (b) broader focus with larger spot size.
The smaller spot size, while producing better definition, risks overheating the anode, so that lower power must be used to avoid anode spot burning (like the burning rays of the sun concentrated by a magnifying glass) Higher power is possible with a larger, broad-focus spot, so there is always a trade off between the resolving power of the tube, and the amount of power that can be applied.
Registered Member #2119
Joined: Mon May 11 2009, 04:30PM
Location:
Posts: 15
Interesting. Thank you for explaining the purpose of the dual filaments.
I'll have to research the tube some and see what information I can come up with. It would be good to know its operating characteristics even if I don't plan on using it any time in the near future. The manufacturing date on the unit, head, etc, are all in the mid 1980's... Specifically, the unit is labeled as being manufactured in 1986. Not surprising that the tube is obsolete, I suppose.
Thank you, once again. I love this board. It's so packed with knowledge and knowledgable people!
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X Ray Head Parts
