The BC-474 transmitter section was "designed" to be powered by the hand cranked GN-44 with the receiver option of being powered by the GN-44 via the FL-10 filter or by a battery similar to the BA-48. The GN-44 generator set is fairly rare but the GN-45 used with the SCRX-284/BC-654 can be found and easily modified to power the BC-474. (Modification is reversible)
K4CHE
Using the GN-45
is not technically correct but it does make a nice "working"
display during Military Rallies and Events. Visitors
enjoy cranking the generator.
CLICK to enlarge
In order to provide proper bias to the receiver audio section the HV section of the power supply B - (B minus) must be above ground. The GN-44 hand crank generator diagram shown above demonstrates the B- (B minus) wiring. The GN-44 is fairly rare but the GN-45 can be used as a substitute and a suggestion for a modification is shown below.
CLICK to enlarge
The GN-45 High Voltage B minus is at ground potential. When using the GN-45 generator to provide voltages to both receiver and transmitter on the BC-474 the B- (B minus) terminal of the generator must be above ground.
More information on the FL-10 filter and different BC-474 power options can be found in another section.
Link to BC-474 power options is at the bottom.
The
basic mod is to isolate the ground return (B -) of the generator terminals
and lift the minus side of the 4 uF filter capacitor from ground. Most
generators have a leaky 4 MFD capacitor and it may need replacement. Connect
the lifted end of the capacitor (5.C.1) direct to the B- terminal of the
generator. Connect the B- of the generator to the main 8 pin connector
5.K.1 pin 3 via a terminal on the relay. Note: The relay is not
used or powered for BC-474 operation the terminal is used as a convenient
tie point. Add a jumper on relay 5.E.2 to bypass the relay
and provide the High Voltage (500V) to pin 8 of the connector.
Shown
above on the right is the High Voltage minus (B -)terminal with new wiring.
One wire goes to the filter capacitor and the other wire to pin 8 of the
main connector.
NO OUTPUT ? Be sure and clean the communicator on the low voltage side as the windings may not be getting enough excitation. Any dirt or residue can prevent proper excitation. I usually use one of those 3M green pads for cleaning.
Shown above the "Leaky" filter capacitor (bottom) has been replaced and a modern cap cable tied in place. A white/blk wire connects the capacitor to the minus terminal of the generator. The relay shown above (upper right) is not used or powered for BC-474 operation. The brown wire connects the minus terminal of the generator to the relay terminal which is used as a tie point to pin 8 of the main connector. The voltage regulator shown in the center is still used and is not disturbed.
A small interface box was used to connect the 4 pin BC-474 cable to the the GN-45 using a fabricated cable and connector. A 5 K resistor was used to lower the B plus. A 6.3 volt light was wired to the 6 volt output. Remember to provide proper voltages to the receiver filaments and plates you must use a FL-10 filter. Link for info on the FL-10 and other BC-474 power options is at the bottom.
A connector was fabricated from phenolic and brass tubing.
The small package allows more options for your GN-45/BC-474. The generator 8 pin male connector is not rare and can be purchased from the usual suppliers. The 4 pin connector for the BC-474 power cable is home brew.
Ready for the Rally
BC-474
FL-10 filter and power options