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Old 24th Mar 2023, 1:43 pm   #21
regenfreak
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Default Re: Step up transformer from 9 to 575 volts for a Geiger tube.

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Originally Posted by Radio Wrangler View Post
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Originally Posted by broadgage View Post
A useful test source is an old stock pressure lamp mantle. Newer production might be non radioactive but older ones contain radioactive thorium.

"Uranium glass" has come to mean a style of glassware that may not contain any actual uranium. Genuine antique uranium glass can be a useful test source, but modern production may not be.
You can get thoriated tungsten electrodes (coded with a dip in red paint at one end) from welding equipment suppliers who sell them for TIG welding. There are also Ceriated and Lanthanated types which aren't radioactive. Alternatively, if you know a welder, he might give you a few stubs left over when too short for the torch to grip. These are typically 2% Thoriated.

Some WWII photoreconnaissance lenses used lenses doped for anomalous refractive index and the dopant was a radioactive salt For added fun the 'hot' element was often the front one and the glass was slightly water-soluble! Do not clean by licking! This stuff after the war turned up in some specialist telephoto lenses as well... until it was thought better to leave this technology behind.

David
I am fascinated by nuclear disasters, radiation and Geiger counters after watching the drama series Cherynobl. You can remove the americium source from an old smoke detector or buy dirt cheap "nap07 ion chamber" from china. I was going to buy some Art Deco uranium glasses and uranium ores from ebay, but I have an irrational fear about anything radioactive..I believe I own a few high-power transmitter triodes which are radioactive but I wont get cancer as long as I don't put them under my pillow.

Even high-quality camera lenses can contain lanthanum,zirconium and thorium dioxide....I still have my Canon 200mm F1.2 L super telephoto lens under my bed for years..but I doubt it is radioactive.

Last edited by regenfreak; 24th Mar 2023 at 1:54 pm.
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Old 24th Mar 2023, 8:08 pm   #22
Cruisin Marine
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Default Re: Step up transformer from 9 to 575 volts for a Geiger tube.

Regenfreak
Which triodes are they?
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Old 24th Mar 2023, 8:38 pm   #23
regenfreak
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Default Re: Step up transformer from 9 to 575 volts for a Geiger tube.

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Regenfreak
Which triodes are they?
One of my high-power triodes is 811A which contains thoriated tungsten filament(mildly radioactive). I can't remember all the names of my high-power triode collection. I am a very untidy person, and they are stored in mountains of junk boxes at home.I have power triodes from the transceivers of the British Spitfire fighter and US Navy fighter planes, all containing thoriated tungsten filaments. Usually, they state it in the valve datasheets.

The Radium Girls used to lick the tips of the paint brushes for the luminous paint. Some highly collectable Leica camera lens are radioactive....
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Old 24th Mar 2023, 8:49 pm   #24
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Default Re: Step up transformer from 9 to 575 volts for a Geiger tube.

I used a 555 oscillator circuit to drive a 240V to 9V transformer in reverse. To get the highest output voltage, I was able to tweak the oscillator frequency to match the resonant frequency of the transformer. I was able to achieve 425V which was sufficient to drive the tube.
Neil
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Old 2nd May 2023, 9:01 pm   #25
Cruisin Marine
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Default Re: Step up transformer from 9 to 575 volts for a Geiger tube.

Just to update: I built and completed the Geiger counter, it was based on the R&EW design from April 1982 issue.

The original will not work as the interfacing in to the 7555 input (pin 2, trigger) is all wrong. You have to bias the pin 2 with 100k resistors to +5 volts and ground and couple in with a 100 nF capacitor from the collector of Q4. The mag is available here https://worldradiohistory.com/UK/Rad...1982-04%20.pdf

I did however, have to build a completely different HT generator based on a flash gun transformer made by Jessops. I drove it it with a CMOS 4001 NOR gate oscillator and a VN10 FET mini power FET running at 9.64 kHz driving the tfmr, the best frequency that the tfmr worked at. Almost any cheap flash from a charity shop (usually £2-7) should do fine for an HT Generator for the Geiger-Muller tube.

I designed it to run from a PP3 and to work down to 8.2 Volts, but it functions well below 7 volts

Testing and Calibration
I tried large transmitting tubes with Thorium/Thoriated filaments as a source, and none showed any readings. An old gas lamp mantle worked very well as a test source.
To calibrate you will need a 100 Hz 1v P-P square wave source, the R&EW article describes how to do it.
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Last edited by Cruisin Marine; 2nd May 2023 at 9:30 pm.
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Old 3rd May 2023, 11:15 am   #26
DrStrangelove
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Default Re: Step up transformer from 9 to 575 volts for a Geiger tube.

Yes, the old gas mantles are really impressive. The new ones not at all.

Much more active than the uranium glass seems to be.

I'd not thought of the flash gun approach.
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