Refurbishing a CD V-700 Geiger Counter

The CD V-700 Geiger Counter was designed and built to Department of Defense Military Specifications. It is a very rugged instrument.To refurbish the CD V-700Geiger Counter for a radiation safety application, it must be disassembled, carefully inspected, cleaned and critical electronic values measured. Necessary adjustment must be made and gaskets and shaft seals replaced or lubricated. Electrolytic capacitors and any suspected parts must be replaced. The unit must be burned in for 4 to 12 hours to monitor stability and to force the early failure of new parts. While a CD V-700 may be new and in very good condition, it may have some touch up paint added by the government calibration lab.The CD V-700 should be accurately calibrated with a National Institute of Standards Technology, N.I.S.T. traceable Cs-137 (Cesium) sourced calibrator designed for calibrating the CD V-700's. To be accurately calibrated for measuring radiation it must be calibrated using an N.I.S.T. traceable Cs-137 source. A CPM pulser only calibrates the electronics counts per minute, not to exposed radiation level. There are a number of factors that affect calibration that occur more or less randomly. The CD V-700 class of Geiger Counters are designed so that the calibration is not sensitive to voltages. As the battery voltage drops or the GM tube high voltage changes, the instrument will remain accurate. Frequently the HV regulation tube is out of specification even on new-old-stock instruments and needs to be replaced. A solid state regulator is best.The geponents that are in the calibration circuit are the GM tube, the meter movement, one or more resistors and one or more capacitors. The GM tube generally remains consistent unless it is damaged by banging it around. The tube will degrade when exposed to high levels of radiation for a long period of time. Most of these instruments have been held in reserve for a nuclear war and have seen little radiation. However, some have seen a good bit of abuse to the point of damaging or destroying the tube.Mil. spec. meter movements, resistors and capacitors change little with time except for electrolytic capacitors and high voltage selenium rectifiers. The electrolytic capacitor operates somewhat like a dry cell battery. They gradually die and should be replaced. Selenium rectifiers degrade slowly with use and should be replaced for proper long-lasting function.. Then, circuit checks need to be made to assure that all of the remainder of the geponents are within specification. If not, the offending parts need to be replaced. Finally, a 6 to 12 hour "burn-in" will trigger infant mortality in any weak geponents that need to be replaced. Periodic recalibration takes care of any long term drift in the geponents. The original manufacturers regemend that recalibration be done every year for radiation safety applications.