Check the listing for details. W2ENY - RF Amplifier Buffer Relay Acc Cable for FLEX 6300 6400 6500 6600 6700. Condition: New. Listed at 45.00 USD. RF Amplifier T/R Relay Interface for Flex An External "Relay in the Cable" interface fits the Flex 6300 6400 6500 6600 6700 by Bob W2ENY MANY amplifier relays draw more AC or DC than what your Flex may support and that's why you need this cable (insurance policy). It simply plugs into the 15 pin accessory rear jack (looks like VGA) on the radio and uses pins 9 and 11. Over five feet of cable to an RCA/Phono type plug that fits to your amplifier T/R relay connector. This package is complete, compact and streamline with all components located inside the connector. Unlike other costly solutions, there is no klunky external box (like ARB-704) or wall wart (psu) Yes there's a relay inside the connector, but looks like a regular cable. So, here's why I offer this... Yes I'll admit it, I smoked my Flex relay with my Ameritron AL-811 amp and had to send it back. This is the solution I came up with, wish I did this before.For the technical types, the circuit uses voltages available on two pins of the radio's accessory jack for switching, operate delay is 2ms. Contacts are rated for 2 amps DC and 0.6 amps AC, much more than the T/R relay in your Yaesu, Heathkit, Alpha, Ameritron, Dentron, Collins, Drake, Henry, Amp Supply, QRO, etc. For Yaesu FL-2000, 2100 (strip off the connector and wire direct to terminal strip)...THIS is the original relay in the cable, thousands in the field with Icom's since 1997.If you have a Flex 65xx radio and an amp, this is what you need, before you send it back for repair! FYI I'll be putting up a Flex page on my site soon, see that pic referenced here - for that price, go to w2eny . com