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Forum 141

Workshop Ekco N645A

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Refugee
(@refugee)
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I got one of these from the flee-market on Thursday. Sadly it is missing the probe so as of yet i am not able to test it and will in any case check it all out for leaky caps if i ever find a probe for it and also an old smoke detector of the correct type

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The condition is mint and that includes the battery connections It is mainly one of those items with a build quality that you can't pass by I am having a go at remembering when i read a magazine article about building a home brew one so that i can get a better idea what i am going to find inside it. I am thinking of making a silicon substitute for the probe and have an optimistic feeling that it might work without changing anything else. It is going to have to join a que behind two bitchy scopes and four radios and also the finishing touches of an EL37 push pull stereo with a big wick to be turned up.

 
Posted : 25/08/2012 3:10 am
crustytv
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Not hijacking your thread just offering up a solution I used. I had a Taylor Model 22 Fault finder which was missing it's probe, I managed to track down the circuit for the probe and used an old solder sucker to build a new one. Example below it works a treat, just an idea. Chris

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Posted : 25/08/2012 10:51 am
Anonymous
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A "rate meter" counts discharge pulses in a tube affected by radiation.

So the probe needs a device sensitive to radiation. The device usually has a thin window to allow the radiation in. I suppose a metal can transistor with lid removed with very high collector volts (adjustable regulated) via high impedance source so it's just below breakdown but can't be damaged by the current might be usable. The chip needs paint to block IR, visible and UV Light.

A neon tube with high impedance voltage source with paint to block IR, visible and UV light, adjusted just below trigger volts might work too.

Really it needs the correct Geiger Muller tube or you are basically just using the box and meter to design something else. A transistor or Neon will not be as sensitive.

Unless it's a counter for something else?

 
Posted : 25/08/2012 11:10 am
Cobaltblue
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I am guessing the probe will use a Geiger–Müller tube so not something you can construct really. You can just find a suitable tube and put in a suitable enclosure that won't block whatever your trying to detect. Cheers Mike T Snap Michael

I don't care if it was a bargain whats it doing on my kitchen table. www.cossor.co.uk

 
Posted : 25/08/2012 11:12 am
Anonymous
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Some types of Barretter have a radioactive coating on the wires

 
Posted : 25/08/2012 12:24 pm
Brian Cuff
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That's a very good idea Chris, using a solder sucker as a probe body. I will remember that one!

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Posted : 25/08/2012 12:53 pm
Refugee
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I was thinking of using some MOSFETS connected in parallel so that the total area of the silicon chips adds up to the area of the original tube.
The exciting voltage is adjustable from 800V to 1400V.
I am going to have to work out a date for it too.
It is going to be interesting looking inside as there will be an inverter of some kind.
I am pretty sure it is solid state as it only has a single 9V supply from six D cells.
We are getting enough interest for me to start thinking about opening it up for my first look inside.

 
Posted : 25/08/2012 1:56 pm
Refugee
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Here is my reveal of what is in this device.
The battery compartment has six screws in it and once removed the plate behind lifted away to reveal the chassis but little else apart from two press studs that run to the tube socket.
Once out a label with more info on it was revealed covering some of the basic servicing.

Now we can get into the more interesting bits.
There was a loose wire on one of the voltage switches on the front panel so i gave that a quick fix and got the PCBs out to reveal a generous helping of OC series transistors and caps dated DEC 1961.
The Hunts caps are epoxy ones and not a bit of wax on any of them.
It does not look like it should draw more than one amp with that germanium PNP on such a tiny heat sink.

 
Posted : 25/08/2012 9:06 pm
Brian Cuff
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What's in that large plastic assembly with what look like diodes round the outside and next to the power trans? As you say, probably a worthwhile purchase for the Ge devices in it. Useless without the proper probe - and not a lot of use with one

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Posted : 25/08/2012 9:48 pm
Refugee
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That potted bit is the up converter for the 1.4KV for the tube.
It does have some very nice shiny OC series transistors and some diodes in the same package with 2 legs some are OA10s.
I could get more than i paid for the transistors on an auction site and get to use a very nice cabinet for something else.
It was reduced to £8 from £10.
It would make a nice cap tester or even a high voltage FET tester with quite a bit of the original components retained.

 
Posted : 25/08/2012 10:23 pm
Anonymous
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I'd use the case for something else and save the OC44s etc for a rainy day.

Maybe a combo capacitor leakage tester / transistor tester with an op-amp driving the meter. I'd guess it's a 250uA, 500uA or 1mA movement thus needs an op-amp?

I'd use the box, meter and all the controls and nothing else.

The 1.4kV module might be reusable for a small CRT to make a portable multi-standard TV or scope, or for insulation testing. Or just parts.

 
Posted : 25/08/2012 10:47 pm
Refugee
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All the components are military quality and the HV generator looks like it might be regulated.
I think the entire PCB would be better kept as a module with the potted transformer and stick diode (hidden behind one of the caps in the photos).
The OC44s look sort of shiny as if they have been painted on a different production line.
The Hunts caps are plastic tubes with resin end plugs and look like even they will be good after all those years.
The probe socket is on the top right hand side of the case and sort of sticks out a bit.
It would have been better on the front or in a recess.
All the same it is a quality project case.
I will do a little more research before i make a commitment.

 
Posted : 26/08/2012 3:26 am
Refugee
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Well i have done an auction site valuation and there are tubes from Ukrane for 25 quid inc postage or a complete unit with tube for 25 quid inc postage that uses a non standard battery.
It looks like i have a nice case that is better than the ones other units have with lovely knobs that knock spots off all the others that are for sale.

 
Posted : 26/08/2012 4:27 am
Forum 157
(@Anonymous 1976)
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@refugee I have one of these counters and I bought it when I was working at Leeds Uni back in 1978. Think it was from M&B Radio. Mine came WITH the detector, so I can tell you what it was. It was a large metal tube with a smaller diameter tube at the end of it. Inside the tube was a photomultiplier. There was a crystal in the small tube and the PM tube was looking for flashes of light produced by scintillation from incident radiation. So its a scintillation counter, hence the discriminator settings you will see on one of the controls. You can set the discriminator  to detect different energies of radiation.

I'm trying to get mine working again, after all these years. I'd love to have a circuit diagram for it to help me work on it.

It is quite possible the unit would work with a GM tube, assuming the GM tube could work at the voltages the unit can supply. I have an alpha GM tube that requires about 1500 volts so may try it with that.

 
Posted : 03/07/2023 8:34 pm
crustytv
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The last time this thread received a post was almost 12-years ago, and refugee has not logged in for many years. I think it's fairly safe to assume, you're unlikely to get a response.

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Posted : 04/07/2023 9:38 am
Forum 157
(@Anonymous 1976)
Posts: 2
 

@crustytv 

Yes I realize that. I found almost nothing about this counter using a google search. This forum and this thread was one of the very few matches. Others might find this thread, so just wanted to say what I knew about the device.

I worked on it last night and got it working enough to try connecting a GM tube to the detector socket. It did show pulses at the right rate for background for the particular PM tube. I know from using the same GM tube, on a Griffin scaler, that the background is about 53 DPM.

At the moment the inverter on the Ekco isn't working properly. The EHT and the other derived low voltages are all too low. The inverter is not drawing excess current to probably not a problem with the transformer.

 

 
Posted : 04/07/2023 4:49 pm
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