This is a new, unused Ameritron model ARB-702 Interface Buffer. Its purpose is to go between a Transceiver's amplifier keying lead and keying line of a linear amplifier, that may have too high a keying voltage to be safely directly keyed by the circuitry in the radio. As best I can tell, it is the ARB-702K version, with the 7-pin plug that plugs into Kenwood radios, such as a TS-440 Transceiver REMOTE jack. Amplifiers such as older Heathkit SB-200, SB-220, some Drake, Alpha, Collins, Swan and other amplifiers can't be keyed directly by the transceiver's keying relay without possibly burning up the contacts in the radio. This Interface is designed to key amplifier relays that have as high as 200-volts DC and/or current of up to 200 mA. This unit needs an RCA plug on a 2-conductor cable to go to your Amplifier's keying jack, which is then internally connected to your Amplifier keying circuitry. It has a 7-pin plug to go to the radio for keying signal, supply voltage and ALC connections. I also have an Ameritron ARB-704 interface and a PNP-7D cable to go to Kenwood transceivers available in a separate listing. $38 shipped to CONUS locations only, payment by check or money order only, no PayPal, no trades. Please contact me with any questions direct to my email address as shown here on QRZ.com: firstname.lastname@example.org , instead of using QRZ.com's message system.