The BC-474 transmitter was "designed" to be powered by the hand cranked GN-44 with the receiver option of being powered by the GN-44 (through the FL-10 filter) or by a battery similar to the BA-48. On these pages we will attempt to offer some ideas of alternative methods of powering the set as well as fabrication of connectors.

           
            Do not ground the High Voltage B- direct to the chassis. The receiver final audio and RF stages will not be properly biased.

             Do not apply 6 volts to the receiver filament chain the receiver uses 1.5 volt filament tubes. The transmitter uses 6 volt tubes.

                          Introduction
                       Connectors
                       FL-10
                       GN-45 Vs GN-44
                       Dynamotor Power
                       Inverters
                       Battery Bias
                       Another Dynamotor

      The BC-474 has two power cables if it has not been ham hacked.
                 One cable for the receiver and one for the transmitter.

          The transmitter power cable uses the large 4 pin male connector.

                                A possible source for the male connector pins.

                                        Outside view of the fabricated connector on a home brew supply.

                
                                    Receiver cord and top of a late model BA-48 battery.

                  The receiver cord uses a standard 4 pin battery connector with male pins.

               When search for a 4 pin battery connector or cable - the cables for other radios such as the GRC-9 may only have 3 pins connected.

               
      
          A little paint or fingernail polish helps. Anyway it ann't that hard.

                                          

                    FL-10 filter diagram. Note that the B minus is above ground. Also note that the generator low voltage of approximately 6 volts (A+) enters at pin 1 on SO-22 and then is dropped by a 20 ohm variable resistor (5) to provide 1.5 volts for the receiver filaments. The receiver B+ is supplied via a 15K dropping resistor from the GN-44 high voltage of 300 Volts. The 20 ohm wire wound variable resistor is perfect and is used to adjust the receiver filament voltage of 1.5 volts. During filament adjustment of the receiver filament chain must be connected to provide the proper load.

               Be careful when testing the receiver tube filaments for continuity with a volt-ohm meter. Make sure that the meter does not supply more than 1.5 volts on the resistance/ohm range selected.

         Do not apply High Voltage direct to the set by grounding the B - (B minus) to the chassis.      The final receiver stages will not be properly biased. In addition audio output will be distorted as the volume/RF gain control will not function properly.

         The BC-474 receiver filaments require a voltage of 1.5 volts - Do not apply 6 volts.

                                 

                            The GN-45 looks like a GN-44 and makes a suitable working display. But has to be modified. Its voltage of 500 is too high for the BC-474 and requires a dropping resistor. A simple internal wiring change will give it a floating ground.

                 
                         Q. Where can I find a GN-44?
                         A. You probably can't.
                         Q. The connector on the substitute GN-45 doesn't match.
                         A. See below.                
                         Q. Why do I need a "floating ground" for receive?         
                         A. Proper bias for the receiver audio and RF stages.
                         Q. Do the transmitter circuits need a floating ground?
                         A. No
                         Q. How do I drop the voltage on the GN-45?
                         A. Use a power resistor of 2000 ohms. 15-20W
                         Q. I don't wanna crank.
                         A. Other power supply options are shown below.
                                       
                         

               
                     Fabricated "Cable Box" with resistor. Fabricated 4 pin connector.

             The Cable Box was used to convert a GN-45 cable for use on the BC-474. The GN-45 was used as display substitute to power the BC-474. The GN-45 provides 500 volts and needs a dropping resistor. A 2000 ohm resistor is enclosed in the box.

                      More info on the GN-45.

                            http://k4che.com/GN-45/GN-45.htm

                       
                                       CLICK to enlarge             N3FRQ Diagram
                                "Floating" B minus Dynamotor needed.
                     A suggested Dynamotor power supply by Al N3FRQ when the FL-10 filter is not utilized. Voltages are regulated. More FL-10 info below.)

              Al -N3FRQ used a 12 volt dynamotor (DM-64-A) found at a hamfest that is used in the BC-923A FM military receiver. The DM-64 dynamotor audio stage.    " I replaced the 6V6's in the TX with 12A6's. The rig pulls about 4.4 A from a 12-volt battery in AM, 4.0 A CW key-down, 2.8 A standby, and 2.3 A receive only." Note the zener network used to provide proper bias. Proper bias is needed for the receiver audio stages.

Al Klase BC-474 dynamotor supply notes: "I've been playing with my MI-8751 (original Swedish version) getting ready for future events. I discovered I had a mistake in my dynamotor power supply design. I had the RX and TX B-'s connected together. This shorts out the 800-ohm resistor in the RX B- that provides bias for the audio-output tube and RF gain on CW. (You don't notice this too much in AM.) I've added a 9-volt Zener in the dynomotor B- line. This regulated voltages swamps the 800-ohm resistor, and everything works five. Drawing attached. I don't know if you were contemplating building one of these or not. The DY-64-A is rated at 275 volts 150mA with 14 volts in. I replace the 6V6's in the TX with 12A6's. The rig pulls about 4.4 A from a 12-volt battery in AM, 4.0 A CW key-down, 2.8 A standby, and 2.3 A receive only. So my 17 AH battery will run it for a while."  

                   
                                              CLICK to enlarge

                            "Floating" B minus Dynamotor needed.
       A another circuit utilizing a Dynamotor and the FL-10 filter. The LM138 regulator is rated for 5 amps. An LM317 (1.5 amp rating) can also be used. The dynamotor needs to have a floating B minus. (4 wires or contacts)                             

     Total current draw for the 4 receiver filaments (1.5 volt tubes) is .25 A. Three (3) of the receiver tubes draw .05 amps and one tube (V4) draws .1 amps.

     Total current draw for the transmitter filaments (6 volt tubes) is .45 X 3 = 1.35 amps

    An interesting note: The average adjustable voltage regulator when used for the filament supply needs approximate 1.5 volts input above the output voltage. In other words for a regulated output of 6.3 volts then approximate 7.8 volts is needed for the input voltage to the regulator. If this keeps you awake at night you can use a Mouser LD1084V a 5 amp low drop out regulator which only requires approximate half a volt ) above the input to function.*

   * Many thanks to Al N3FRQ for the suggestion.

                       

              When considering a dynamotor for powering the BC-474 receiver and transmitter the simplest solution is to have a floating" B - (B minus)
but be aware that many of the dynamotors do not have the B - terminal insulated above chassis.
The terminals of my hamfest acquisition a DM-53 are shown above. The left side is high voltage + (plus) and the right side is - (minus). The left side is insulated but the right side is not.
      Provisions for bias will have to be made for proper receiver stage operation when using this type of dynamotor on a BC-474.           More info below.

                      

           This DM-25B dynamotor utilizes insulated terminals for each input and output. The dynamotor is rated for 250 volts at 50 ma and during bench testing it provided enough power to run the set. Even at 10 volts there was sufficient voltage to run the receiver and transmitter at reduced power. Below 9 volts input the modulation on AM drops off but CW operation is OK and is sufficient for demonstrations at a military meet or rally.

                    

                                             DM-25 dynamotor.

          Here is a PDF file of a dynamotor list downloaded from the amfone.net site. Author unknown.
                            Dynamotors and Hand Generataors for the Experimentor
    Here is a link to Ray Robinsons Dynamotor list.
    Ray Robinson' Site Dynamotor list

         Robert Downs suggested that there are some possible 12 volt candidates that have a isolated HV B minus output.

       12/14 V dynamotors with floating B- brushes are: DM-34-A (BC-604) and 211042 (TCS) but output is only about 220 VDC from 14VDC in. 21215 (RU) 300VDC/0.163A from 12VDC in. 21454 (GF/RU) but output @ 14 VDC in is 425 VDC DY-10/ARC-4X Output 360 VDC/0.160A from 13VDC in. That's all that I can think of in 12 to 14 VDC input. I have at least one of those except for the 21454 (assuming I can find them). The DY-10 has a bent fan according to my database but I may have a DY-9, too.

                     

             What ever method of power you choose if you are worried about the bias voltage and want to check it - The R22 bias resistor is easy to locate. Check the voltage on the Tube side of the 1 megohm resistor- it should be around minus 9 volts with respect to the chassis.

                 
                           GE Exect One series commercial 2-way radio.
         Something to look for at a Hamfest.

          The older commercial two way radios have HV inverters.

     The power supply section of the GE radio is mounted in this box for portable 12 volt ops

                        Q. What about the "floating ground"?
                        A. The GE supply can be confirgured for B minus above ground.
                        Q. How do I obtain the lower B plus voltages?
                        A. This partiular GE supply has an output for 300 volts.
                        Q. What about filament voltages?
                        Q. I used seperate voltage regulator IC's on a heat sink for the filaments.
                        Q. What about connectors?
                        A. You will probably have to fabricate them.
                        Q. Why not put it all in a smaller box?
                        A. Go for it.
                        Q. This web page jumps around and is confusing.
                        A. I know but there is a lot of info.

                              

           Another possible solution for HV. Available on ePay. Advertised as a DC input 12 to 24 to DC 200-450V 70W "high voltage converter" boost step up power supply. But the battery input A minus and the HV output B minus are tied together and provisions will have to be made for bias. I have tested this supply and it certainly will power the set and will do so well below 12 volts. Keep in mind that the output B- (B minus) is tied to the input A minus. So provisions for bias have to be made. BUT there are solutions shown below.

                Here is a video I made during bench testing of the above inverter supply.

              Inverter supply filter version.

          
                                    
                          Grounded B minus Inverter or 3 wire Dynamotor utilized.

                       Another circuit by Al N3FRQ but this version has not been bench tested . The builder will probably sub a 6 volt and 3.3 volt zener in the TX FIL(-6V) and RX B- (-9V) voltage circuits as the 3 volt zener is not readily available.
                        

                

           Using the 9 volt battery to provide receiver audio and RF bias allows the use of a "non floating" dynamotor or a imported ePay switching inverter.

           
                Q. How much drain does the BC-474 bias circuit impose on the 9 volt battery?
                A. Less than 5 ma. (.005 amps)
                Q. I am worried about the battery running down and then I lose my bias..
                A. When using your volumn/RF gain control listen carefully - - If the audio starts to                degrade your battery is getting low and it is time to change.
               Q. Does the bias have to be exactly 9 volts? See below.
               A.      No

               Q. I don't think I can fit a 9 volt battery into the bottom of the reciever.
               A. Don't be a weeny - give it a try. But if all else fails use a smaller battery. SEE BELOW.

                Smaller battery packs are available. You can use a lower or higher bias voltage by a couple of volts. Many smaller battery packs are available for voltages less than 9 volts.

               
                              Click to enlarge

        9 Volt bias battery installation. Connect battery minus to R15 lug 3. Positive of the 9 volt battery to chassis ground. Locate the white wire that runs from R15 to TB1 and disconnect at TB1 to isolate the bias line and prevent draining the battery. Insulate the end of the disconnected white wire.
                 OR - - - - -
       Just disconnect white wire at TB1 Lug 1 and connect the 9 volt battery minus to the end of the wire with positive going to chassis ground.     Do not change anything at R15 lug 3.

                    

        There is a white wire running from the R15 lug to TB1 it is dressed along the "rear" of the receiver chassis. When using an internal 9 volt bias battery mounted near the front panel mounted R15 - - - disconnect this wire from lug 1 of TB1 and insulate the end with spaghetti. (The white wire is dressed along the rear of the receiver chassis.)

                  OR

      You can mount your battery near the rear of the chassis.  Locate the white wire and disconnect at TB1 and connect bias battery.

                     
                                                                                    K4CHE

                                              A operating display.


                     Return to Top of page.                     

                            Return to K4CHE Index