CN-690 Notes

           Some notes on the CN-690. There was a e-mail post on one of the mil lists several years ago that there was a wiring error within the unit.

      Quoting the e-mail: "The harness from the handcrank genny to the radio is 'spose to be a regulator, but the resistsor is AFTER the regulator tube, not before it, as it should be! The tube will overheat and burn out if the harness isn't re-wired. Been there, correct that ..."

             There are no wiring errors in the CN-690 regulator cable or circuit.


                   CN-690 Regulator Assembly and Cable for the GRC-109 and RS-1.



 General info from the manual

                                     CN-690 Schematic

     Looking at the schematic of the CN-690 it does indeed show a resistor "after" the OB2 and there is no value printed on the schematic. The resistor is a 470 ohm 1/2 watt device and is not the primary series current limiter for the tube. Note that the transmitter is not effected. CR1 is a selenium rectifier for the receiver filament
                         R-43 Schematic

                                               CLICK to enlarge

             A series current limiter for the OB2 is installed in the R-43 generator. A 10K resistor is connected from the high B plus line of the generator to pin 21 of the generator power connector. This 10 K resistor is the main current limiter for the OB2.

                                        R-43 generator output wiring.

                    CN-690 Schematic

        R1 a 470 ohm 1/2 watt resistor provides a very small amount of current limiting for the 105 volt circuit and also because of the small wattage ( 1/2 watt) it serves as a protection device in event of a short in the receiver. It is not the primary series current limiter and is installed in the correct position. R 1 a 470 ohms resistor has nothing to do with proper operation of the OB2 (Zero B Two).
                              Figure 45

              The small 470 ohm 1/2 watt resistor is shown on figure 45 as R1.

                       The OB2 rests in a rubber shock mount assembly. The tube can be changed quickly by removing the box cover. You can easily take a peek and see if it is glowing.


                    Socket wiring. Only two pins are utilized.


                          Franks Electron Tube Page OB2 Data Sheet

                   Note that in the above OB2 data sheet diagram that when the tube is pulled the HV will be interrupted which was common practice in older radio equipment but in CN-690 only two pins are wired.

                     Franks Electron Tubes pages





                Last time I checked Murphy's Surplus they had the CN-690 in stock.

                                                   Murphys Surplus Web Site



        The regulator and its cable can also be utilized if you construct a separate power supply for the RS-1/GRC-109. The power supply shown above can also be also used for the BC-1306 and GRC-9. In any event the constructed power supply will need a high wattage limiting resistor for the voltage regulator tube in the CN-690 with a value of between 10K and 15K depending on your high voltage.


       The CN-690 regulator can be used with other generators such as the GN-58 and PE-162. GN-58 schematic below.  
                              GN-58 Schematic
                                           CLICK to enlarge

                        GN-58 also has a 10 K resistor connected to pin 21
                         PE-162 Schematic
                               Click to enlarge

                The PE-162 gasoline generator has a 10K resistor - study the schematic carefully.
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