systems_glitch

Troxler Portable Scaler 200 B

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A friend discovered this being junked from his department's lab:

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It's a Troxler Portable Scaler, Model 200 B. It seems to be one of Troxler Laboratories' first products: the date on the (now dead) internal battery was 1958!

This device seems to be a nuclear decay counter, of very high precision. It runs on Dekatron tubes, which are the old vacuum tube equivalent of a decade counter/divider. Unfortunately, it was left outside in the weather for a day before being discovered, so it's not entirely in working condition. All but one of the Dekatrons, however, are functional -- the one that wasn't got cracked (allowing air to enter the glass envelope, thus ruining the tube -- which was originally neon-filled, rather than containing a vacuum).

It seems to contain some very early "integrated circuits" -- small PC boards containing modular circuits, using octal tube sockets to connect them to the rest of the equipment:

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Inside:

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Notice the old silver-can transistors -- they are 2N1404 /Germanium/ transistors!

The design and wiring in the device is immaculate:

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The tubular bases of the actual Dekatrons contain a small "integrated circuit" as well:

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All of the pictures are stored here: http://computernik.cjb.cc/images/Scaler/

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Awesome, now you just need nuclear decay.

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Very nice! Based on the date, 1958, it was either very well taken care of or not used hardly at all.

And if you need a radioactive source try tearing apart a smoke alarm. I've heard the smoke sensors are radioactive.

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Unfortunately, I don't have the Geiger-Muller tube probe for it! For those who don't know, a Geiger-Muller tube is used to detect radiation: it's a vacuum tube, in which a high voltage (usually > 700 V) is applied. When a radiation particle (gamma, beta, or alpha) crosses the vacuum and strikes one of the plates, a current flows for a very small interval. This is what causes the characteristic clicking in Geiger counters -- it can also be used as a pulse into a counting circuit.

From what I understand, it broke some time ago and got stuck in a storage room, where it lived for a while. When they were cleaning it out, no one could remember or figure out what it was, only that it was marked as non-working.

Except for having been left in the weather (they'd sat it on the curb for my friend to pick up, and a bit of rain got in it) and a cracked Dekatron tube, it seems to be largely intact. The high voltage circuit seems to be dead (which would've provided a HV supply to the Geiger-Muller tube, if I had it). I've plugged it in, after drying out the circuit modules, and the AC Charging light lit up, along with three of the Dekatron tubes. However, when I switch on the HV selector, everything dies, and a high-pitched noise can be heard.

The HV circuits (there's two...one for the 400-500 V supply to the Dekatrons, and a 1000-15000 V supply for the HV probe) are pretty neat: they use simple resistor-capacitor networks with two transistors to drive toroidal transformers!

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Micro Geiger Mueller Tube

Only $34.95... Come-on.... You know you want it. ;)

That probe looks like it's too small, though -- the voltage requirements are too low, and it's designed /primarily/ for detecting gamma radiation. For the most part, anything I'd be checking would be alpha/beta emitters.

However, it would be really cool to build my own Geiger counter...I could either work up my own driver circuit, or use one similar to the CDV-700 (the extremely common Cold War Civil Defense Geiger counter). That might be something to consider when I get a little extra cash!

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