Information provided by: Paul, W9AC
Amplifiers can damage a FLEX-6000 TX Relay line if the amplifier has too much relay control voltage, voltage spikes, or excessive current on the relay control line. Such damage often appears as "stuck" or "sticky" transmit relays in exciters or shorted transistors on transmit control lines. In most cases where the radio is damaged, the system transmits normally but the external amplifier stays locked in a "transmit" mode. This prevents receive signals from coming through the amplifier with normal levels whenever the amplifier is in the "ON" or "OPERATE" position.
The ARB-704 is compatible with all common radios and amplifiers even though radios and amplifiers do not have standardized keying voltages, accessory plugs, or wiring. This interface is designed to work with any amplifier/radio combination and is good "insurance" to protect your FLEX-6000 from damage regardless of the amplifier used.
Based on the ARB-704 manual, it would be connected as follows:
1) ARB-704 TX-SEND jumpers set for LOW SYSTEM;
2) ARB-704 J2 (Radio) connects to the Flex 6300 TX Relay KEY line;
3) ARB-704 J1 (AMP) line connects to the amplifier key line.