View Full Version : Hoffman Countmaster geiger counter

Johnny L.A.
08-16-2005, 09:17 AM
I have a Hoffman Countmaster geiger counter (http://www.orau.org/ptp/collection/surveymeters/hoffman.htm). I was going to eBay it as part of my continuing 'Clean Out My Life' campaign, but my partner says it's a perfect prop for our film. So I'm looking at this thing, which is still stored in its original box and has the original manual.

The power for this thing is made up of eighteen 9v batteries and two AA cells wired in series, plus four D-cells in their own holders. 171 volts total. The manual says that the high voltage check should be 900 to 975 vdc. I assume there is a transformer inside?

Does anyone know what kind of batteries this geiger counter originally used (c. 1955)? Was it common practice to use 'build-it-yourself' batteries? Or are the 9v batteries an attempt by someone to replicate the original power supply? I'm not an electronics technician, so I can't read the schematic; but I see BT1 15v, BT2 & BT3 75v each, and BT4 1.5v.

What are the odds this thing -- now 50 years old -- still works?

Johnny L.A.
08-16-2005, 09:19 AM
:smack: This was supposed to be in GQ!

Will someone please 'Report this post' so a mod can move it?

08-16-2005, 06:07 PM
Moved to GQ.

samclem GQ moderator

08-16-2005, 07:34 PM
It wouldn't use a transformer for a DC source but there are other types of semiconductor non-svoltage multipliers.

08-17-2005, 07:29 AM
Johnny, I hate to burst your nostalgia bubble, but geiger counters were dangerously unreliable. Often, by the time it detected rads, the person using it had already had a major exposure. They also had, in your case have, a high incidence of injury due to electrical shock.
Hubby know s a bit about their history, from his haz-mat classes. Nothing about how they were set up though.
I remember, one of my Jr High science teachers had one. The battery was, as I recall very much like a tiny car battery, the old style, with a bunch of holes to put water and acid in. My memory of it is vague, after all that was 45 years ago.

Johnny L.A.
08-17-2005, 07:57 AM
Johnny, I hate to burst your nostalgia bubble, but geiger counters were dangerously unreliable.
It doesn't need to be accurate. We're thinking of using it as a prop, so all we need is for the needle to move and for the lights to flash. (I wonder, if it works, if it would pick up one of my watches? The one with the nuclear trefoil and 'DISPOSE OF RAD WASTE' on it?) Anyway, it's never going to be used seriously; but I like machines that are funtional.

08-17-2005, 08:22 AM
Just don't kill yourself, 'k?
If you do get it working and have access to any old dishes, like Fiesta ware, the red/orange glaze will ring its chimes.
You'll have to get it to make that cool, old movie gieger counter sound too. :D Nothing else sounds quite like it.
The science teacher I spoke of, took my favorite rock away from me :( because it set his off from the next room. Probably 25 feet. It was probably a false reading. I want my pretty, bright blue rock back!

Johnny L.A.
08-17-2005, 09:43 AM
No, no old dishes. I got mine from Pic'N'Save (now Big!Lots) maybe five years ago. No 'dinner stes' for me! I purposely mixed up the colours. Anyway, the're cheapies from Mexico or China or someplace.

I wonder if I could take the gieger counter to an electronics shop in town and just have them fix it?

Oh -- for the film, it has to pick up 'ectoplasmic radiation'. ;)

08-17-2005, 12:01 PM
The 9V batteries in series are probably a jerry rigged replacement for a "B" battery.

A,B,C,D batterys were origionally intended as bias, plate, heater, etc. power for early tube type radios. The lower voltages were found to be useful in things like flashlights, and so persist today. Once AC power became widespread, there was no need for the B batteries, and they became extinct. Their legacy lives on, however, as the plate supply in vaccum tube circuit diagrams (which still claim a few applications) is invariably labled "B+"

Johnny L.A.
08-18-2005, 09:01 AM
The 9V batteries in series are probably a jerry rigged replacement for a "B" battery.
I dimly recall reading one of Cecil's columns on B-cells.

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