As you guys know, I'm a retired nuke. Recently I found some mailing lists for serious amateur nukes and that has caused me to "get my nuke on" again.
One thing a lot of people were complaining about was the lack of a suitable high voltage driver for the many surplus X-ray tubes that are available. Only rarely does a transformer show up and then, at least for diagnostic X-ray machine, the things weigh in at around 600 lbs.
So I volunteered to design one. The target is 150kV at 20 ma.
This driver is based roughly on the quasi-resonant architecture and uses GM HEI coils in parallel to achieve the desired power level. They are operated in oil for cooling and insulation.
I use the GM P/N DR37T coils. At the suggestion of a reader, I took a look at the DR35. This coil has spade lugs for primary connections and is a beast compared to the DR37T. The page will be updated to reflect the new coil choice.
So far I've achieved 120kV with the DR37T and 5ma using one coil. The voltage is limited by the approx 1000 volt flyback on the 1200 volt driver transistor. The new DR35 should take it to 150kV at a yet-to-be-determined output, as the ratio is higher. Plus I've equipped the transistor with a high joule Panasonic ZNR type TVS designed to clip at 1050 volts. That will protect the transistor in case the knob-twister gets a bit too enthusiastic :-)
I intend to use this driver with a very large therapy tube with a liquid cooled anode so this driver is designed for continuous duty. I'm interested in studying the effects of radiation on materials. Cross-linking, radioluminescence, etc.
It works equally well driving one coil to generate low voltage for things like XRF. Voltage in the 10-20kV range are easily achieved with a HVDC input of about 12 volts and one coil.
Of course, this thing has other uses than driving X-ray tubes. The pulses are mono-polar so a rectifier isn't necessary but a diode and a capacitor can be used to produce smooth DC. I set up a 200kV rated diode stack and 5uF 150kV capacitor with this unit and generated some truly scary sparks.
This thing is extremely rugged. The output can be shorted, operated open-circuited (in oil, of course), allowed to arc back to the transistor collector, all without damage. The only thing that will damage it is turning the charging current up too high so that the primary flyback voltage exceeds about 1100 volts. The transistor's absolute rating is 1200 volts and it'll do that - for a little while.
Operation with the corona discharge "dummy load" pictured on the web site quickly fills the cabin with enough ozone that I need to run the whole house fan. It electrifies everything in the vicinity from the sprayed electrons. I had a Crescent wrench laying on some refractory flash over to an earth ground from the charge build-up. I wear my anti-static wrist strap when operating this thing to keep from getting a static zap.
Someone on the mailing list commented that this would probably also be useful to the Farnsworth Fusor guys. I'm not really up on the details of that project but I do know that it requires a pretty hefty source of high voltage.
I have set up a private mailing list for discussion of this and related projects. Anyone who is of majority age and can comport themselves properly is welcome to join.
Finally here's a vid of one coil running at about 90kV
Bare PCBs are available from fluxeon.com. It's not in the store yet so write Garett Churchill, snipped-for-privacy@fluxeon.com. $12. If there is enough interest, we'll offer A/T boards also.
The BOM isn't on the site yet but it'll go up in the next day or two. Garett is collecting Digikey and Mouser part numbers for all the parts.
John John DeArmond