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Steampunk Geiger Counter, Part 3

With the rash fading and the nerve pain lessening (and Carol safe home!) I stole an hour or so downstairs last night to see what could be done in an hour or so downstairs. And I did well: I got a spark gap together, all made out of junk I’ve had lying around here forever. Not much to it, really: Some brazing rod, two husky black 5-way binding posts, and a battered 4-row barrier terminal strip. I had to drill out two of the holes in the barrier strip to pass a 10-32 thread, but apart from that, the only work was grinding points on two pieces of brazing rod and adjusting the binding posts so that the brazing rod pieces met point-to-point.


Done. Didn’t test it; ran out of evening. However, I did put 450V on my capacitor bank to make sure the caps were good, and it took a right-fine charge. It was interesting to watch how quickly the 450V bled off into the probes of a 50,000 ohm/volt VOM. (I miss my old Heathkit VTVM, may have to pick up another.) The more capacitance, the more energy is stored from the spark rectifier, and the longer the counter will run without another crank on the interrupter. So as time allows I’m going to put together a second plug-in cap bank.

The next step is to lash up the interrupter circuit to see if it can charge the caps and make sparks on the above rig. The rotary interrupter still needs some work, but I can clip-lead in an SPST pushbutton switch to give it a go.

Damn, but it feels good to get my hands dirty again. And let me tell you, boys and girls, there is nothing quite like the smell of a gallon milk jug packed full of 40-year-old black Bakelite barrier terminal strips!


  1. Tom R. says:

    Ah, yes! The smell of old Bakelite in the morning — er, evening….

    I Love it Jeff! Glad Carol’s home and doing well (at least I assume she is).

    1. If I had my druthers it might well be morning and evening, but real life exists and real work has to get done.
      I’m pleased to report that Carol has begun transitioning from a clear liquids diet to a mostly mush diet, but trust me, that’s a big step forward!

  2. Lee Hart says:

    Great to hear Carol’s getting better.

    A spark gap rectifier works better if the electrodes are asymmetric; cathode side sharp, anode side flat. Look inside an OZ4 rectifier for an example.

    1. Heh! I never knew that! And although I’ve broken open and examined the guts of tubes many times (once under an inspection microscope I’d borrowed) I’ve never done that with an 0Z4.

      And it would take me about fifteen seconds to do the mod: All I have to is flip one of the two electrodes so that the flat side faces the point on the other. Will try to get to that this evening, if I can work in any playtime.

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