Detectron Geiger Counter
Yes it uses some kind of step-up circuit, and the output to the GM tube is
about 300-400 volts.
"N_Cook" wrote in message
...
Chris F. wrote in message
...
I recently bought an old Detectron model DG-7 geiger counter. This is
from
the early 50's and has three 1U5 tubes inside. Power requirements are 90
volts for the B+, two "D" cells for the tube filaments, and a 4.5 volt
bias
supply.
I went over the unit, replacing a selenium rectifier and testing the
tubes. The unit powers up, but generates a steady stream of pulses on
it's
own, even with the probe detached. The frequency of the oscillation
varies
with the range selector knob. The probe is working - when brought near a
source (a bunch of vaseline marbles) it will produce extra clicks in
addition to the stray ones generated by the unit.
I've checked all the other components - resistors, capacitors, etc. The
only thing I couldn't check is a very small tube, which looks like a
cold-cathode rectifier of some kind. I've also tried varying the B+ and
bias
voltages. And I can't find a schematic, which makes matters worse.
I'm not sure what to do next. Any ideas?
90V seems low for a GM, is there a step up circuit to 300V or so ?
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