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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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20th Nov 2022, 8:57 pm | #1 |
Nonode
Join Date: May 2016
Location: Cornwall, UK.
Posts: 2,335
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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. |
21st Nov 2022, 3:27 pm | #2 |
Nonode
Join Date: May 2016
Location: Cornwall, UK.
Posts: 2,335
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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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21st Nov 2022, 4:30 pm | #3 |
Tetrode
Join Date: Nov 2022
Location: Near Worcestershire/Gloucestershire border (in WR), UK.
Posts: 70
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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. |
21st Nov 2022, 4:51 pm | #4 |
Heptode
Join Date: Feb 2022
Location: Leicestershire, UK.
Posts: 690
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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 |
21st Nov 2022, 4:59 pm | #5 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,015
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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. |
21st Nov 2022, 5:13 pm | #6 | |
Dekatron
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,209
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Re: Contamination Meter No. 1 no reading
Quote:
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21st Nov 2022, 5:24 pm | #7 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,878
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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.
David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
21st Nov 2022, 5:27 pm | #8 |
Tetrode
Join Date: Nov 2022
Location: Near Worcestershire/Gloucestershire border (in WR), UK.
Posts: 70
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Re: Contamination Meter No. 1 no reading
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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21st Nov 2022, 5:53 pm | #9 |
Octode
Join Date: Nov 2003
Location: Bath, Somerset, UK.
Posts: 1,805
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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.
Neil
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preserving the recent past, for the distant future. |
21st Nov 2022, 6:43 pm | #10 |
Tetrode
Join Date: Sep 2020
Location: Lewes, East Sussex, UK.
Posts: 66
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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.
Des |
24th Nov 2022, 7:09 pm | #11 |
Nonode
Join Date: May 2016
Location: Cornwall, UK.
Posts: 2,335
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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. |
24th Nov 2022, 7:37 pm | #12 |
Dekatron
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,209
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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. |
24th Nov 2022, 7:41 pm | #13 |
Nonode
Join Date: May 2016
Location: Cornwall, UK.
Posts: 2,335
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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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24th Nov 2022, 8:25 pm | #14 |
Pentode
Join Date: Feb 2020
Location: Camborne, Cornwall, UK.
Posts: 128
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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 |
24th Nov 2022, 9:57 pm | #15 |
Heptode
Join Date: Jun 2010
Location: Zurich, Switzerland
Posts: 538
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Re: Contamination Meter No. 1 no reading
Background radiations clicks are actuell in most regions between 0,1--1-5 secundums...
K. |
24th Nov 2022, 9:57 pm | #16 |
Octode
Join Date: Feb 2006
Location: Bristol, UK.
Posts: 1,042
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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 |
24th Nov 2022, 10:04 pm | #17 |
Hexode
Join Date: Aug 2010
Location: Malvern, Worcestershire, UK.
Posts: 347
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Re: Contamination Meter No. 1 no reading
My ex Slough civil defence contamination meter used DLR No.5 headphones.
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25th Nov 2022, 11:44 am | #18 |
Dekatron
Join Date: Aug 2003
Location: near Reading (and sometimes Torquay)
Posts: 3,095
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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? |
10th Dec 2022, 12:11 am | #19 |
Nonode
Join Date: May 2016
Location: Cornwall, UK.
Posts: 2,335
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Re: Contamination Meter No. 1 no reading
Thanks all. The Langrex GM tubes arrived today, and I'm getting some kicks of the needle at random intervals so I guess all is well internally! I'll be in touch about some 'phones, roadster541. VT FUSE - do you happen to know the type of plug they need? I'd love to hear some clicks!
I wanted to avoid going through the whole manual, GMB, before checking the tube so as to avoid unsealing the unit again, doing the drying and adding extra chances of damage. As you might imagine, Cornwall's pretty moist... I think I overheated the dessicant in one of the inserts, or perhaps the indicator paper as I suppose the dessicant is pretty inert. Maybe I'll replace it at some point. |