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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
Hi, the tubes finally turned up.
Connected to GM counter and they seem to work, now just need to build a power supply. Any suggestions for something relatively low powered?
(note: soldering to pin isn't a good idea but I pre-tinned the 3 ply twisted EC wire used and set soldering iron to its lowest possible temperature then heatshrunk around the wire so it can't move)
Also after some 120V zener diodes, as ebay seem to have problems when I try to order them.
Registered Member #230
Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284
I use TVS diodes as high voltage regulators suggest SMAJ110A from littlefuse. they are better than zeners except for accuracy of breakdown point, but the knee is much sharper
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
I use a simple voltage doubler on the mains to get 600V at the few tens of microamps required.
For safety's sake, I use two miniature PCB mains transformer wired back to back (e.g. 230V to 24V, 24V to 230V) by way of mains isolation. I'm sure this is not at all efficient, but as we are only talking microamps nothing is lost by it.
I put a 68M bleeder resistor across the output of the voltage doubler, to stop it storing up nasty surprises!
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
Should work, thanks.
The tube current measurement transformers used on flat panel monitors if once side is rewound might also work. EDIT: a low tech low power (tm) alternative might be a modified piezo transformer using a simple single transistor (12V) buzzer clamped to to the piezo cell from a gas lighter. As I am only looking to generate relatively low voltage it would just need a feedback circuit and the slight noise should be a non issue. Might even put this one on Hackaday! EDIT: It *almost* works, getting the piezo out intact turned out to be more difficult especially on a used lighter. What I really need is something which outputs a stable 130-380 volts but is only a single 8 pin SOIC, and additionally contains the measuring and I2C outputs. Surely a "single chip dosimeter" isn't impossible with Supertex having >280V output EL drivers now and the recent ones can even set their output voltage independent of frequency. Also handy would be if the measuring circuitry inside the chip also compensated for temperature and tube aging. And if by magic,
EDIT: Tried a new approach using HV850 but with an active rectifier modified Marx-generator like setup made from optocouplers running on Vmax 4.3V offload 53V p-p 6N135 is usable but better to use an SOIC version where possible as this is well within the ratings and its just a matter of SMD soldering. Advantage here is that in principle it is fail-safe: one lost opto just drops output voltage by a predictable amount. so you can compensate with software if required.
It appears that the original block modules actually use a circuit very similar to the one used in gas lighters, with a unijunction transistor pulse generator driving a small transformer and 2 stage C/W multiplier.
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