Check the listing for details. Elecraft KX-3 Amplifier Keying cable. Condition: New. Listed at 22.95 USD. Amplifier keying cable for Elecraft KX-3 radio to your amplifier keying circuit *Connect the 3 conductor 2.5mm plug into your KX-3 rear ACC2 jack, then plug the RCA cable into your amplifier keying jack (usually labeled "relay" or "RLY"). Cable is 5 feet long. *** NOTE: DO NOT exceed the rating of the switching on your KX-3! We HIGHLY recommend our RBI-1 relay interface between any radio and your amplifier to isolate the amplifier relay control voltage and current from your radio amplifier T/R switching circuit Connector color may vary on RCA male connector. See our eBay store listings for our complete line of Amplifier Relay Buffer Interfaces. In other listings we have models with 2 radios and a bypass switch, 2 or more amplifiers or other device (like noise reduction unit keying, mute, etc) When connecting your Radio and Amplifier, there may be switching voltage, polarity, and current incompatibility that can cause damage to your radio or amplifier if connected without a switching interface between them. Even if your internal radio switching looks like it might be usable, it is wise to have an extra degree of isolation between your amplifier and radio with our relay buffer interface. 73, Dan W7RF ( Radiodan ) Ham Radio amplifier amateur amatuer radio amplifier relay buffer interface