Interface for Amplifier Control

The circuit displayed below was designed by Ted, K9IMM, to provide an interface between his IC-756 and Alpha 77.  I have used the circuit with Icom and Flex radios to control Kenwood TL-922A, Heath SB-220 and Drake L4B amplifiers.  I presently use a variation of this circuit between my Flex 5000A and homebrew amplifier*.

Printed circuit boards can be obtained on request.  Since some amplifiers (such as the SB200 and Henry amps)  use a negative voltage to key the relay, the board has an option to use a inexpensive 3A reed relay instead of FET's.      

*  In the homebrew amp, another FET switch is also keyed by the VN10P.  That FET controls the 100V tube bias and provides the necessary delay to make sure the antenna relays are closed before high power is run through them.