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Electro-Neutronics Inc.

CD V-700 Model 6b


This is a Geiger counter originally used for Civil Defense purposes. This came in non functional.  I checked all the semi conductors, diodes and transistors.  I went through the resistors and found them mostly in tolerance.  I tested the meter with an ohm meter and a 10k series resistor.  I started with a 1 meg resistor and worked my way down dividing by half until the meter registered 1/2 scale.  That satisfied me if the meter was good or not.

The unit came in with a spare used G-M tube.   It only needed the loose pins super glued.  Once the new G-M tube was in I measured about 600 volts on the tube.  The scope showed the typical fly-back transformer weird wave shape by simply putting the probe tip near the fly-back transformer. 

This was something new for me to work on.  A hybrid mix of solid state and a G-M tube.  It was fun.  See the pictures below.

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This schematic is inside the case. 

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Restored and operational. 

The probe holder and yellow stand-off is with the owner.  He want to mold and duplicate a new one before the original breaks clean through. 

IMG_6499.JPG (2531913 bytes)Pre-restoration

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Check CR6 Zener voltage of 15.5 at the collector of V4 fly-back oscillator.

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Collector of V4

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Glued plastic battery holder spacer.  

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The G-M tube ground depends on these two case contact points.  They were pained and I did not like that.  A file cleaned off the paint to establish a reliable ground. 

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Calibration on the right.  I do not have a cal procedure nor do I have a radiation standard.  






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