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Old 20th Nov 2022, 7:57 pm   #1
Uncle Bulgaria
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Default Contamination Meter No. 1 no reading

Finally the film capacitors arrived from Odessa and the Contamination Meter's leaky paper capacitors have been replaced. It amused me to fix a UK Cold War artefact with Soviet components from Ukraine as a gesture of international amity.

All capacitors were tested before use. I've just finished baking the assembly in the oven for two hours at 50C, as the instructions require. The dessicant is reset to grey. The vibrator supply hums and the needle rests in the middle of the 'Test' section when the 'test' switch is operated.

However, I have no 'kicks' as expected from background radiation. I haven't got a radiation source, but guessed I should get a signal from a Tilley lamp mantle. No dice. I have two GM tubes, one with a rattle and the other with the removable cap for testing water. Neither give a reading. I haven't got a suitable set of headphones to see if there's any audible signal. Both headphone contacts are ~170V above the chassis.

Are there any tests I can do without taking it apart and drying it again? I see the manual has some voltage test points, but the pictures of the boards are wiped out in the photocopying so I'd have to trace the circuit.
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Old 21st Nov 2022, 2:27 pm   #2
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Default Re: Contamination Meter No. 1 no reading

Could it be both GM tubes at fault? Measuring anode to probe case at the tube socket gives ~170VDC, and the meter needle kicks significantly as the meter probe is applied.
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Old 21st Nov 2022, 3:30 pm   #3
PaulDarzi
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Default Re: Contamination Meter No. 1 no reading

Recent Tilley mantles have little or no Thorium - you need old stock for the Thorium doped versions 1970's or older IIRC.

You may have better luck if you have (or can borrow) old pocket watch or pre 1950's wrist watches with lumious marks - they are usually super emitters especially the Radium based paints.
Sometimes a trawl around second hand shops can turn up either suitable watches or alternatively "uranium glass" ware https://en.wikipedia.org/wiki/Uranium_glass aka Vaseline glass - which are great test sources.
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Old 21st Nov 2022, 3:51 pm   #4
Roger Ramjet
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Default Re: Contamination Meter No. 1 no reading

On another post, Tim mentioned that early Trimphone dials contained Tritium which was radioactive. Hamid then went on to say that by now the Tritium by now would have exceeded it's half life period.

My query would be ... what element has the Tritium decayed to & would that still be radioactive ?

Same goes for Radium paint on watch faces ?

Rog
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Old 21st Nov 2022, 3:59 pm   #5
Jon_G4MDC
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Default Re: Contamination Meter No. 1 no reading

Find a Big Ben by Westclox from the 1960's.

My physics master was horrified by one. It would glow all night long and bright enough you could read by it.
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Old 21st Nov 2022, 4:13 pm   #6
TonyDuell
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Default Re: Contamination Meter No. 1 no reading

Quote:
Originally Posted by Roger Ramjet View Post
On another post, Tim mentioned that early Trimphone dials contained Tritium which was radioactive. Hamid then went on to say that by now the Tritium by now would have exceeded it's half life period.

My query would be ... what element has the Tritium decayed to & would that still be radioactive ?
Tritium (Hydrogen-3, 1 proton, 2 neutrons) emits a beta particle (hence the TRIMphone light tube is called a Betalight) and becomes Helium-3 (2 protons, 1 neutron) Helium-3 is stable, not radioactive.
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Old 21st Nov 2022, 4:24 pm   #7
Radio Wrangler
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Default Re: Contamination Meter No. 1 no reading

TIG welding electrodes. The red marked ones are thoriated (2%) Tungsten. More available now than old gas mantles.

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Old 21st Nov 2022, 4:27 pm   #8
PaulDarzi
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Default Re: Contamination Meter No. 1 no reading

Quote:
Originally Posted by Radio Wrangler View Post
TIG welding electrodes. The red marked ones are thoriated (2%) Tungsten. More available now than old gas mantles.

David
But not from Amazon (or, at least, not the ones I tried - yes, they did have red tips) others suggested visiting a local garage or someone who welds locally and asking for an electrode from them, unless you can use a pack of them?
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Old 21st Nov 2022, 4:53 pm   #9
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Default Re: Contamination Meter No. 1 no reading

I tested the tritium tube in my trimphone a few weeks ago using my Soeks Defender radiation meter. Absolutely no response. Tritium has a half life of only seven years so I am not surprised. A good test source would be an old alarm clock or compass.
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Old 21st Nov 2022, 5:43 pm   #10
deswradio
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Default Re: Contamination Meter No. 1 no reading

Remember that tritium decays, emitting beta particles at very low energy. Geiger tubes are usually designed to detect gamma (and high energy beta) radiation - for a beta particle to enter a geiger tube, you need a pretty thin window.

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Old 24th Nov 2022, 6:09 pm   #11
Uncle Bulgaria
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Default Re: Contamination Meter No. 1 no reading

The Tilley lamp is an old one, new in a box. Regardless of the mantle's radioactivity though, the CM1 manual says that 'kicks' from background radiation should be visible on the meter, and I've seen none. I've ordered a new GM tube from Langrex as a check.

I want to see if there's any clicking in the headphones - does anyone know what headphones would be suitable? The contact are two sockets ~9/16" apart, a little more than 1/8" diameter. The manual states no 'phones were included with the sets. I guess the contacts shown in the attached snip of the circuit diagram are the headphone sockets, which are labelled "5K 2". Perhaps a characteristic impedance? Is that a normal military value?

The 'phone sockets are floating about 170V above the chassis. I guess they're supposed to be as the sockets have hefty rubber insulation.
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Old 24th Nov 2022, 6:37 pm   #12
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Default Re: Contamination Meter No. 1 no reading

I think 'SK2' simply means 'SocKet 2' and is a component referenece like 'R1' for a resistor.

The user manuals says that 'Suitable Headphones -- Receivers, Headgear, I.T.E No. 1B J.S.C. No, 5965-400046.' whatever those may actually be.
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Old 24th Nov 2022, 6:41 pm   #13
Uncle Bulgaria
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Default Re: Contamination Meter No. 1 no reading

Aha! A good interpretation. Funny - I thought I'd seen a reference to a long JSC number and went through all the manuals before posting...and missed it entirely. I had previously searched for any online reference to what that number means, but didn't come up with anything.
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Old 24th Nov 2022, 7:25 pm   #14
roadster541
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Default Re: Contamination Meter No. 1 no reading

My No1 came with a pair of, what I have always assumed to be, DLR phones. I will have a look when I am at home. I have several spare sets of 600ohm DLRs if you would like one.
Where we live, there is plenty of background radiation to keep the meter flicking.
Rod
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Old 24th Nov 2022, 8:57 pm   #15
karesz*
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Default Re: Contamination Meter No. 1 no reading

Background radiations clicks are actuell in most regions between 0,1--1-5 secundums...
K.
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Old 24th Nov 2022, 8:57 pm   #16
Malcolm G6ANZ
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Default Re: Contamination Meter No. 1 no reading

You can check the function of the instrument by disconnecting the GM tube and linking the place where it was with a high value resistor. By intermittantly touching one end to the circuit you can simulate the action of the GM tube. When an ionised particle enters the tube it allows a very small current to flow this is amplified and causes the clicks and a reading on the meter. If the meter works and you hear clicks then the circuit is working. The tube should show open circuit in normal conditions.
In Cornwall there ought to be plenty of background radiation from the granite.
Apologies if I'm stating the already known
Malcolm
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Old 24th Nov 2022, 9:04 pm   #17
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Default Re: Contamination Meter No. 1 no reading

My ex Slough civil defence contamination meter used DLR No.5 headphones.
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Old 25th Nov 2022, 10:44 am   #18
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Default Re: Contamination Meter No. 1 no reading

I think the No.1 would be best served by high impedance phones, otherwise it looks like the meter readings would be affected.

Check you are getting enough voltage from the PSU.
You did do the tube voltage setup procedure?
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