I’ve found this two interesting modules at Marzaglia ham radio flea market (11 May 2019) and bought for 5€.
Each module have soldered two geiger tubes, one per side and a signal conditioning/high voltage generator circuit.
The tubes are ZP1210 made by Valvo during 70’s I think. Valvo company doesn’t still exist but Centronic.co.uk still make this tube. It’s a design original made by Philips and made by various brands under licence.
ZP1210 gamma geiger tube Lenght: 140mm Plateau threshold: 400V Plateau lenght: 100V Plateau slope: 0.15%/V Counting rate at 10e-2mGy/h: 110 count/s Dead time: 200uS Background shielded: 70 count/s Dose rate range: 3x10e-4 / 10 mGy/h
The onboard circuit seems in working order. I’ve tryied to feed it with 12/24/30V dc and obtained 160V across tubes with 30V input. I don’t know the correct voltage needed by it’s circuit. I don’t know how the circuit output it’s counting pulses. I’m thinking that this two modules are from a steel scrap radiation detection system. They probably are feed with a relatively high voltage like 48Vdc or 70Vdc and the output pulses from the tubes are used to modulate the power supply line. I’m thinking about scrapping the four tubes and as much as possible from the electronics but I’m not a fan of bit tru-hole components from the 70’s. With 5€ I’ve bought 4 very nice geiger tubes with very good characteristics… I’m very happy!