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Grenadier's big thread of RÃ¶ntgen related shenanigans

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magnet18

Sun Jul 10 2011, 04:11AM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

Got it finished yet?

Adam Munich

Sun Jul 10 2011, 12:09PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Control box is repaired, just need to build the head when I'm feeling more motivated, and find a sheet of butyl rubber.

Xray

Sun Jul 10 2011, 02:47PM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Grenadier wrote ...

Control box is repaired, just need to build the head when I'm feeling more motivated, and find a sheet of butyl rubber.

McMaster-Carr Supply

Adam Munich

Tue Jul 19 2011, 04:21AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Decided to start working on this again today, cracked open two vacuum rectifiers and used the bases to make a cable (needs a bit of "finishing" though). Then I plugged it in the sockets and started wiring things up.

HV musth share a common ground with the ucontroller, and it tended to restart the uC when it was turned on. After replacing the mosfet switch with a relay the problem was reduced but not eliminated. I think some sort of NTC thermistor or a large cap after the inductor on the zvs could reduce the voltage spikes that cause things to reset. Or maybe installing the actual cw and x-ray generator could solve the issue (or make it 10x worse).

Managed to blow out the transistor on the linear reg though... have more coming in the mail but that means the project's on hold for a few days.

Adam Munich

Thu Jul 21 2011, 01:57AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

So... my lipo charger died after I dropped it, cracked the LCD and failed hard at replacing it. Hobbyking is out of lipo chargers and I'm pretty much fuk'd now...

magnet18

Thu Jul 21 2011, 02:43AM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

If it's any consolation, I overcurrented the nixie driver on my clock and fried it (apparently 12ma is not the same as 20ma...) and I think all the 4017's, and probably all the transistors (one for every freaking number >:()
seems like were in similar boats.

Adam Munich

Sat Jul 30 2011, 05:57PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

The cable is done. It's a bit short at 4 feet though... ran out of wire. When I get some more wire (and 2 more tube sockets) I will make a longer cable, maybe 15 feet. In the meantime I'll just press expose and walk away while the timer counts down for a few seconds.

Pretty satisfied with it. The wrapped string and octal bases give it the 'old' look I was going for. JB weld secures the wires in the bases.

Now I went to paint the last part (tubehead lid) yesterday, but seems like I bought some faulty paint because it failed to hammer. Returned the can and got a new one, and once the crappy layer is done curing (tomorrow) I'll try a new coat.

Adam Munich

Sat Aug 06 2011, 05:56PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Hey guess what it works!

<< Dosimetry Video

Well it did work... until I borked it.

The x-ray was working just fine until I decided to add a little capacitance to the ZVS. It was my hope that this would lower the resonant frequency and impedance, and allow more current to flow in the ZVS. It did, and I got 500uA more in the coolidge tube. I then decided to add a bit more capacitance, and that killed it.

Here is what I think happened based on the damage; When the relay turned off the ZVS, the larger currents did not want to stop flowing and a small arc formed in the switch. In order to sustain the arc the LC tank raised its voltage, and since I'm a dumbass I put the TVS diode on the relay side after 4 feet of cable. Because of that it did jack shit, and the higher voltages over by the ZVS punched through the mosfets' gate and latched them on. This exploded the large voltage regulator and shorted out the battery, and since that is a LiPo about 300 amps flowed for a few milliseconds. When the fuse burned out, another inductively fed arc formed inside there and that caused a high voltage on the 14.4V rail. This burned out the 5 volt buck converter, and let 14.4V flow into all the microelectronics, thus popping every bit of silicon in the system. Including the nixie tube boost converter. The EL wire inverter also exploded, so I have to wait for the mail for another one of those. The *only* thing that did not explode was the buck converter that powers the x-ray tube's heater, and I'm dumbfounded at how robust it is.

I decided to bypass the microelectronics and just connect power to the zvs with long wires. It failed to work. The power was there, the mAmeter pegged and there was no kilovolts. Uh oh...

After drawing an arc from the unheated tube I came to the conclusion it was gassy. Well... what do I expect for such a cheap tube. It's a wonder anything works in china! I'm going to replace it with a CEI tube, and being made in italy that thing should be a hell of a lot more robust.

Now what to do with the gassy tube... I'm thinking nightlight or flashlight, seeing as the heater is still OK.

Proud Mary

Sat Aug 06 2011, 06:14PM

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

Grenadier wrote ...

After drawing an arc from the unheated tube I came to the conclusion it was gassy. Well... what do I expect for such a cheap tube. It's a wonder anything works in china! I'm going to replace it with a CEI tube, and being made in italy that thing should be a hell of a lot more robust.

Now what to do with the gassy tube... I'm thinking nightlight or flashlight, seeing as the heater is still OK.

What 'seasoning' regime did you use with the new Chinese tube, Adam?

I don't understand the role of 'drawing arcs' in determining the status of an X-ray tube.

Aren't most of the world's electronic components made in China?

Adam Munich

Sat Aug 06 2011, 08:43PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I followed this guide:

After taking apart the tubehead, it turns out that the HV punched right through the tube. This was one of my initial concerns, because of the conductive lead shielding and the thin glass. I compensated for this by putting oil between the lead and the tube, but when the heater cut out the oil stood no chance against the increased voltage.

I'm not really crying though. This tube wasn't the best of quality anyway and judging by the burn mark on the anode, its focal spot was 1.5mm (though it was *supposed* to be only .7mm).

This CEI tube I'm going to use is bigger, has thicker glass and a .5mm focal spot. It's an all around better tube, and should provide all around better images.

When I rebuild it I'm also going to make sure that the HV cuts out if the heater does. Should have done that in the first place...

Also going to insulate the tube from the lead better.

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