September 25, 1985

CPG 4-1, Volume 6, CHG 1
CD V-700M

(CD V-700M)
The retrofit of the ENI CD V-700 has been designed to accomplish a slight change in function and to improve the instrument's overall performance and efficiency. To meet these goals, these modifications have been made:
•An end window probe (OCD-P-108) containing GM tube type OCD-D-109 has replaced the original GM tube and probe. The OCD-D-109 tube is a selected Amperex Model 200LB, which has been modifed by placing a 1 pF capacitor in parallel with a 10 ohm resistor mounted in the base housing of the tube. -"' tube high-voltage supply of ~575 volts was selected to ensure a useful tube life. In some cases, it is possible to operate this tube in the 900- to 925-volt range of the standard CD V-700; however, it will limit tube life. The OCD-D-109 tube has a window density of between 1.5 and 2.0 mg/cm2. It may or may not detect the presence of alpha particles because of the thickness of the dag coating on the window of the tube. This coating is necessary to prevent the tube from responding to visible light and/or ultraviolet radiation. This tube has a much higher beta-particle detection capability than the thin wall tube it replaces. This is particularly true at low beta energies. The overall x-ray and gamma energy (spectral) response of this tube is currently unknown.
•The detector high voltage has been modified to be compatible with the new tube, to be better regulated, and to be more efficient to improve battery life.
•Improving the HV circuit made the addition of a low-voltage converter circuit necessary.
•The original meter has been replaced with one having a calibration in "counts per minute" only and a response that more closely matches the performance of the circuit.
•A two-cell holder from a Lionel CD V-700-6b has replaced the original four-cell battery. This helps to eliminate the poor contact problem and can be accomplished because of improved circuit efficiency, thus prolonging battery life.
•The circuit modifications have been accomplished by modifying the original PC board slightly and by adding a small retrofit board.
•Components R12 (2.7M), CR4 (rectifier), CR6 (regulator diodes), and R13 (lK) have been removed from the PC board. Refer to your CD V-700-6b (ENI) schematic for location and the modified schematic showing the change. A 100K resistor and an 820K resistor replaced R12, and a 0.01 uP capacitor was added to the high-voltage output circuit.

CP 4-1 Pages 27-1 and 27-2