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GE 1000 X-ray tubehead info

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McFluffin

Tue Sept 23 2014, 04:50AM

Registered Member #119 Joined: Fri Feb 10 2006, 06:26AM
Location: USA
Posts: 114

The GE 1000 (from the GX 1000 machine) seems to be pretty popular and a number of them can be found on eBay. I picked one up off of local craigslist that I'd like to use to make x-ray PCB inspection machine (I already have a USB x-ray sensor). Despite there being a lot of them out there, it seems hard to find info on them.

Info I've collected so far:

Does anyone know anything about these units?

(for those afraid I'm going to kill myself: I work with proton beams and other nasty stuff at work already)

EDIT:

Tonight's results:

-X-XC @ 115V draws *roughly* 0.15A (say 17 W). Measured resistance 19.2 ohm. Likely the filament. No increase on geiger counter
-A1-P1 about 0.5 ohm
-MA cannot register resistance on my multimeter to anything. I found some tube schematics online that indicate it may be a current measuring shunt
-G is chassis ground
-With only very slight AC voltage applied to A1/P1 I get a spark on MA to chassis. Aborted for the night. No increase on geiger counter
-Have not tried simultaneously powering both transformers

Steve Conner

Tue Sept 23 2014, 09:23AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I believe you are supposed to connect a milliammeter for tube current between MA and G. The meter completes the HV circuit, hence the spark when it's not connected. If you're not using a meter, MA should be shorted to G.

Wolfram

Tue Sept 23 2014, 10:25AM

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

I believe you are supposed to connect a milliammeter for tube current between MA and G. The meter completes the HV circuit, hence the spark when it's not connected. If you're not using a meter, MA should be shorted to G.

Spot on!

X-Xc is the filament transformer, don't power it from 115V, normal filament running voltage is usually 50 - 70 V RMS, depending on the tube type inside the head.

The HV transformer has a ratio of approx 1:700, so you get 1 kV peak on the tube per volt RMS on the input. The effective output impedance of the transformer is around 500 k, leading to a drop in the HV of 500 V per mA of tube current.

The transformer can handle the full 115 V in, giving 115 kVp, but the tube might not, so increase the HV carefully. Moisture in the oil is a common problem with these heads. This leads to internal arcing, turn down the HV immediately if this happens.

McFluffin

Tue Sept 23 2014, 04:11PM

Registered Member #119 Joined: Fri Feb 10 2006, 06:26AM
Location: USA
Posts: 114

Perfect! That did it: I just ran a low power test and got a reading on my counter.

I don't know the type of tube in there and don't want to disassemble unless I absolutely have to. I'll stick to 50V max for now. Seems a bit odd to me though, why isn't the max voltage on this transformer the same as the other transformer?

One more q: what is the proper way to modulate the tube? Can I keep HV always on and only switch on the current circuit when I need illumination?

Any reccomended learning resources I should look at?

EDIT:

Someone said I should modulate the HV primary instead of the filament primary. Sounds like the primary reason is that the tube takes some time to warm up but also probably safer in general.

Setup pic:

The left variac controls the filament primary and the right metered variac controls the HV primary. The kVp gauge isn't hooked up but does works so I'll hook it up once I start integrating. Finally, there is a geiger counter sitting on a box just under the table (not shown).

Also my geiger counter shows there is noticible leaakage out the sides...I thought it was going to be more beam like. I've ordered about 200 lbs of lead bricks to make an enclosure. I have no idea how much was actually needed but I'm sure this will do :)

Wolfram

Wed Sept 24 2014, 08:21AM

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

McFluffin wrote ...

I don't know the type of tube in there and don't want to disassemble unless I absolutely have to. I'll stick to 50V max for now. Seems a bit odd to me though, why isn't the max voltage on this transformer the same as the other transformer?

Knowing the tube type is not critical, I would leave it as it is. If the control box came together with the x-ray head, it should give you an indication of the max safe voltage. Even if you took out the tube, you would most likely not find any more information on it. The safest bet is to look at the datasheet of a similar tube to get an idea of maximum ratings. This

tube is of a similar size, so it should not be too different.

These x-ray heads were made in different variants, with different tubes, but always with the same transformers. So AC input voltages for nominal operating voltage on the tube depends on which tube is inside. In addition, the x-ray machines using these heads usually had the option of running at independently adjustable anode voltages and filament currents, so there would be no point in having the transformers run at the same voltage.

For tube modulation, it depends on what you want to do. The tubes will often emit some x-rays with HV applied but without filament voltage, so just shutting down the filament is not a safe way to shut off the x-rays. If you need to turn it on fast, leave the filament running and turn on/off the HV transformer. Just don't leave the filament running constantly, as it has a limited life.

McFluffin

Sun Jan 25 2015, 06:15PM

Registered Member #119 Joined: Fri Feb 10 2006, 06:26AM
Location: USA
Posts: 114

"The transformer can handle the full 115 V in, giving 115 kVp, but the tube might not, so increase the HV carefully. Moisture in the oil is a common problem with these heads. This leads to internal arcing, turn down the HV immediately if this happens."

So...after using it for a while it arched. Looking into what I should do moving forward: can it be repaired, etc.

Its sloshy as I shake it around. Is that normal or should it be nearly full of oil?

EDIT:

looking at

I took out that plug and no oil comes out. Its dry in there... In fact, that plug has a hole in it. wtf? I got it directly from the dentist office that was getting rid of it so I don't think it was tampered with in any way.

EDIT2:

Looks like there is an air bladder there and this might be expected. Maybe in his video he pierced it to drain the oil and just didn't show it

klugesmith

Mon Jan 26 2015, 09:02PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Hi Mac. IIRC, we live in adjoining towns. Want to meet up for a tubehead clinic? Check your Private Messages at 4hv. Last year you replied to one after many months.

Wolfram

Tue Jan 27 2015, 06:20AM

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

There's a separate hole for filling oil, it should have a round cap that can be unscrewed.

McFluffin

Tue Jan 27 2015, 06:36AM

Registered Member #119 Joined: Fri Feb 10 2006, 06:26AM
Location: USA
Posts: 114

Yeah, opened the other cap and I drained the oil. Its amber colored (ie not black from charred components) with some black and red (silicone) solid debris. From my very limited view into the unit I don't see any damage.

I picked up some new mineral oil and am trying to dry it under vacuum but it just keeps bubbling after 24 hours of vacuum and the pressure is somewhat high (at least 12 torr). Trying to figure out ways to dry it faster like maybe try to mist it or drop it slowly to increase surface area. I have a lot of silica gel. Any reason to not try that? I also could heat it if need be but would prefer to avoid that.

There are a few cheap GE units on eBay right now, might try to pick one up just in case

PM'd klugesmith

McFluffin

Tue Feb 24 2015, 06:28AM

Registered Member #119 Joined: Fri Feb 10 2006, 06:26AM
Location: USA
Posts: 114

i'll try to post more details soon, but I took apart the x-ray head yesterday. From a quick look over things, I think the filament transformer failed leading to an open on the high voltage transformer. Without a proper path is punched through the plastic shielding to strike the grounded laminate.

Fortunately, the damage to the HV transformer was minimal and I was able to save it:

thats at about 85VAC (75kV?) with about a 2" gap. Funny story, I had to stop due to severe EMI issues in the garage (my "off" vortexer a few feet away was turning on as well as some HVAC equipment much further away)

Anyway, I also have a lot better understanding of how this thing is put together. In particular, its an AC x-ray system which explains why my DC current measurements gave me 0 mA. I also did acquire some more heads from that eBay auction and tested at least one of them good. I'll collect some better data to get more proper drive voltages (in particular on the filament) and hopefully they'll last longer this time :P

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