25B Range Booster AM-4477/GRC

© Brooke Clarke, N6GCE

RB-25B Range Booster sitting on PRC-25


The packaging for this two part Range Booster looks very much like a PRC-25 or PRC-77 except it's only 2.5" high instead of 4.125" like a PRC-25.  The width and depth match a PRC-25 or PRC-77
The Amplifier label says:
Range Booster
Type RB 25 B No. 31182
A/S Bravour Denmark

and the Battery Box type power adapter says:
Power Supply
Type SF 25 B  No. 15245
A/S Bravour Denmark

March 2007 - this is an AM-4477 Range Booster Amplifier and is covered in TM-11-4477-1 which is not a standard military TM, but instead one printed by Associated Industries.

Auto antenna tuner and provides 22 to 30 Watts output over 26 to 76 MHz.

"When used in a vehicle the CY-2577/VRC 24 volt power supply mount is used instead of battery power. 
The CY-2577 adapter box has a lip on the rear, which is designed to fit on the rear of the AM-2060 Power Supply/Audio Amplifier. You will see a bracket on the rear of the AM-2060 with 3 screws. These come out, the bracket comes off, and the CY-2577 takes their place."  Stuart

Reverse Engineering

Power Supply

The Power supply has no active components, it's just an interconnection and relay control box.  It has 3 connectors:
  • The socket that mates to the Range Booster Amplifier looks like a standard BA-4386 battery socket.
    Pin B is ground
    Pin A is the main positive voltage output.  This is probably +28 VDC
    Pin C has no connection
  • The small 4 socket DC Power input connector may be a GC07A8-4S
    Pin A is ground
    Pin B is the control signal to a Hi-G 2B-1506-33 relay with a 650 Ohm coil. Probably a 28 volt coil.
    Pin C is the actual amplifier DC power input, probably +28 VDC at no more than a few amps
    Pin D has no connection
  • A 12 socket connector may be for some type of remote control
    Pin C is ground
    Pin M is the same control signal as on Pin B of the 4 socket Power Input connector
    Pin N may be a monitor pin that has the same voltage as is applied to the 4 socket connector pin C after going through the relay and 10 Amp fuse.  This could be connected to an indicator lamp.
    Pins A, B, D, E, F, H, J, K and L have no connection.


May be called a TNC-250.  The top is similar in size to the BA-4386 but it maybe 3 times taller.
Ni-Cad chemistry.  20 "D" cells.


The front panel has the following controls and connections:
  • BNC(f) RF input from radio ANT bnc out connector
  • 12 socket connector just like the one on the back of the power supply, except this one has a lot of wires connected.  This can be connected to the AS-1729 antenna base (MX-6707) to set the frequency band.
  • OFF, 6 Watts, 30 Watts switch
  • ANT BNC(f) connector - to 50 Ohm type antenna either vehicle or base station
  • <>Female threaded Antenna connector that appears identical to the one used on the PRC-25 and PRC-77, including an internal switch that would be activated when the AB-591 base is installed to indicate a 3 meter long antenna as opposed to the AT-892 1 meter tape antenna that would not activate the switch.
    Can be used for either the 3 foot tape (AT-892) or the 10 foot fishing pole (AT-271) antenna..
Based on the above it appears that this is a VHF Low band Range Booster.  It would have two functions, in transmit mode it increases the power of the wide band FM modulated signal from a receiver transmitter and in receive mode it may have a low noise amplifier, but in any case it needs to have a transmit receiver switch.

The complexity looks about the same as the RF amplifier associated with the OF-185.  In both of these cases the RF amplifier is not a simple power amplifier, like would be used for a CW, AM or SSB signal, but instead essentially regenerates the FM modulation on a stronger carrier.

CY-2577 Vehicle Adapter

This box replaces the battery box and has a standard military vehicle 4 pin plug for 24 VDC power input.
Am-4477 + AM2060 + MT1029

Mil Vech Pwr In Conn

Radio Side of PS
Note that the battery connector looks very similar to the connector on a BA-4386 or BA-5598, but it's in a different orientation and the "D" keyway is rotated.  This is because the battery is a "24 Volt" battery, not the 12 V type used with the PRC-77.  With 30 watts out and 50% efficiency a battery putting out 24 volts will need to supply about 1.6 amps.
Inside PS showing dual breakeers
The circuit appears to be a zener that will cause the breakers to trip if there's an over voltage on the input.

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page created 16 Jan. 2004.