Amplifier Interface for Icoms
An External "Relay in the Cable" interface fits Icom 720, 730, 740, 745, 751
by Bob W2ENY

This cable is used for connecting any non-Icom external amplifier to the older Icoms 720, 730, 740, 745, 751, 751A.

There is no internal relay in these rigs and the circuit will only support a maximum of 24 volts DC at 1 amp. MANY amplifiers draw more than that and that's why you need this cable.

It simply plugs into the accessory rear jack (rectangular type) on the radio. Over four feet of shielded cable and an RCA/Phono type plug fits to your amplifier T/R relay connector.

This package is compact and streamline, all components located inside the connector. Unlike other solutions, there is no klunky external box and no need to apply other external power. Although there's a relay inside the connector, it looks like an ordinary cable.

For the technical types, the circuit uses voltages available on three pins of the radio's accessory jack for switching. Contacts are rated for 2 amps DC and 0.6 amps AC, much more than the T/R relay in your Heathkit SB200, 220, 230, Ameritron AL-80, 82, 811, 1200...., Dentron GLA-1000, Clipperton.., Collins 30S1, 30L1.., Drake L4, L7.., Henry 2K, 3K.., Alpha, Amp Supply, QRO, etc. Yaesu FL-2000, 2100 (strip off the connector and wire direct to terminal strip)...

This is the original relay in the cable.

If you have an older ICOM radio and an amp, this is what you need! 

$45 Complete
Includes shipping by USPS First Class Mail

Send check (US Only) or money order in US$ to:

Robert Langston
286 Hudson Street
Cornwall-on-Hudson, N.Y.  12520
U.S.A.