X ray woes / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

X ray woes

1 2 next

Move Thread

LAN_403

climatex

Sat Aug 06 2011, 11:27PM

Registered Member #2012 Joined: Sat Mar 07 2009, 10:22AM
Location: Slovakia
Posts: 45

Folks, I'm trying to create an x-ray setup... Long story short, the high voltage supply is of the quasi-resonant design from Dr. Kilovolt's schematic, like so:

, pri 9 turns, cap 330n, power source 20V 120VA.

Substituted the 250N with IRF630, no real problems with that one, managed to get at least 45-50 kV unloaded, spark could be drawn to 8-9cm's max, so I thought it would be a good setup for the tube.

The tube itself is an old Chirana, Czechoslovak production, direct tungsten heater, test run was on 3 ampere heating (this value was obtained from a similar Czech experimenter with these chirana tubes, he got 0.2mA of current passing through the tube with 40 kVs on the input, 3.3A heater, no problems radiographing fluoroscopy in real time with rare earth green emitting intensifying screens), I've experimented with 2.0-3.5A heater and also with the potentiometer in the generator circuit, adjusted the frequency (output voltage) numerous times.

The problem... It does emit radiation, but not enough to capture radiographs in real time, on a fluoroscopy screen (I own the 800 "RAPID" sensitivity screens, based on rare-earth). Seems like there's too low radiation output, I don't have a radiometer yet, but I'm getting one, along with a calibrated ionisation chamber to detect high radiation intensities.

Also notice the faint blue glow near the anode when the heater is at 2.5-3A.. at the end of my video, the heater drops to 2A since the heater battery was discharging and the blue glow had went away, the radiation emission was still the same, maybe somewha better.

Sorry folks for writing this in a hurry (01:25 AM here), but I'd like to know your opinions. Should I forget about these single transistor flyback topologies and crank fifty kilovolts from ZVS or halfbridge circuits, or something? I dunno why I'm unlucky here. I thought this supply was sufficient enough...

In the past I've also tried to play with similar single-transistor flyback drivers combined with 6BC-1s and DY86 tubes; got no radiographs either.. :(

climatex

Sat Aug 06 2011, 11:31PM

Registered Member #2012 Joined: Sat Mar 07 2009, 10:22AM
Location: Slovakia
Posts: 45

This is the same chirana tube with 3.3-3.5A heater running on "40 kV 200uA" supply, the author is that Czech experimenter I've informed you about. Eh, just for comparision. Am I just unlucky? :D

climatex

Sun Aug 07 2011, 11:29AM

Registered Member #2012 Joined: Sat Mar 07 2009, 10:22AM
Location: Slovakia
Posts: 45

Ah, okay, no problem. If anyone has got any idea what might help in this case I'd be very grateful. Now I'm thinking about building a two-flyback monster supply, ZVS lets say, but got an advice which stated that it wouldn't be very smart. xD

dude_500

Sun Aug 07 2011, 05:00PM

Registered Member #2288 Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179

Have you monitored the voltage at the tube and the current? It sounds like maybe you're getting 40-50kv with no load, but perhaps only 10kV when you draw 0.2mA. It is common for under-powered ferrite high voltage supplies to have massive v-drop under very tiny load currents.

climatex

Sun Aug 07 2011, 08:35PM

Registered Member #2012 Joined: Sat Mar 07 2009, 10:22AM
Location: Slovakia
Posts: 45

No kilovoltmeter nearby, but I surely thought that the output power would be sufficient enough. At least most quasiresonant drivers generatre more than a few mAs on the output.

Well folks I'm currently re-doing my ZVS driver (single DST flyback, Uin 32-36V 4-10A, two IRF 540s, output voltage ca 20kV, arc max 11cm long). I was thinking about a solid way on how to drive two flybacks with it; their secondaries being connected in series. I've seen this on youtube two times...

and

. What I don't get is the meaning of that little "lnsulation" transformer, with two (or three) leads sticking out for the driver, and 2 x 2 for the two transformers.

Or if there's any way to modify the ZVS driver to output at least 40-45kV's with a single DST flyback on 35V Uin I'd be very grateful, folks. I think that neither tuning the primary down to 3+3 turns nor messing with the resonant cap would make any significant difference in output voltage (+- 15 kV), but I might be wrong... I hope I am, here.

Best regards.

climatex

Sun Aug 07 2011, 08:44PM

Registered Member #2012 Joined: Sat Mar 07 2009, 10:22AM
Location: Slovakia
Posts: 45

Or... something like this, folks?

2mpby91

radhoo

Mon Aug 08 2011, 07:12AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

dude_500 wrote ...

Have you monitored the voltage at the tube and the current? It sounds like maybe you're getting 40-50kv with no load, but perhaps only 10kV when you draw 0.2mA. It is common for under-powered ferrite high voltage supplies to have massive v-drop under very tiny load currents.

Indeed probably this is the cause of not getting x-ray emissions.
Would be great if you could do some measurements, maybe using a high voltage probe we would see what's going on there.

Regarding the power supply, I got some nice results using a ZVS+Flyback+Multiplier, have a look here:

The power supply itself is herE:

Another interesting thread started by Linas, here:

cedric

Mon Aug 08 2011, 01:45PM

Registered Member #2941 Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143

same here ,if you are a bit short in hv current ,you have to control precisely your heater temperature for maximum emission: not hot enough ,very few "hard" x-ray ,to hot and you produce a lot of x-ray but they don't pass the class envelope, you need at list 20 kv to see some thing passing through the tube...

climatex

Mon Aug 08 2011, 03:26PM

Registered Member #2012 Joined: Sat Mar 07 2009, 10:22AM
Location: Slovakia
Posts: 45

There seems to be at least some x-ray emission, it makes the geiger counter go real nuts from a significant distance; plus when the video's maximised, random radioactive "dots" can be seen flying over randomly. So it indeed creates some X-rays but not enough to light up a Corinex screen... hmm.

I'll try the dual-flyback ZVS driver to see if it helps.

Regards climatex

Conundrum

Mon Aug 08 2011, 04:33PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

If its any help I have a few odd HV rectifier diodes here.
Most salvaged, some new.
PM me?
5642 or something.. maybe someone has a use?
I also snagged a somewhat broken but intact vacuum diode from the junk box...

As for measuring, I have a spare screen that Proud Mary kindly sent me, with a simple
modification of a CdS sensor this could be used for sensing X-rays.
Or modified linear CCD etc with scintillator and graduated metals along its length..

-A

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob