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How do you connect an amplifier to the Flex-6500? I'm using an AL-811H

Hello, I am trying to get my AL-811H connected to the Flex 6500 however not able to get the radio to key the amp. Help?


  • John Betner
    John Betner Member
    edited September 2013
    Maybe this is just a **** question but I haven't been able to figure it out lol
  • George KF2T
    George KF2T Member ✭✭✭
    edited February 2019
    There is an RCA jack (actually 3) on the rear panel that serve as relay outputs to switch external devices, like amplifiers. Connect to the PTT in on your amp, and you'll be good. One warning, make sure the voltage and current you're switching is within the range the relay will handle, especially if your amp has a mechanical relay that might "feature" a voltage spike from th coil.
  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited March 2017
    Also set up the TX Relay parameters in Radio Setup->Transmit for your radio too.
  • Ed baker
    Ed baker Member ✭✭
    edited September 2016
    the transmit set up : Thanks Tim
  • Bob G   W1GLV
    Bob G W1GLV Member ✭✭
    edited June 2020
    John , the best way to connect the Ameritron 811H is to use a rig buffer like the Ameritron ARB-704. The amplier you are using is a tube job, the transmitter is an expensive transistorized transceiver. For 60 bucks you can't go wrong. Follow the instructions from Ameritron and you will be good to go.
  • Ed baker
    Ed baker Member ✭✭
    edited September 2016
    You really should be reading the MANUAL 811H PDF pages 2, and 5. In the Amp instructions there is your answer The keying circuit is 12DC @ .100 ma .
  • VE2MBT
    VE2MBT Member
    edited November 2019

    For MINE, i use the Heil FS-2 for the EXACT same set-up, there is 2 wire on the pedal, 1 for the amp, 1 for the radio.  The pedal KEY the Ameritron few milisecond BEFORE it key the radio !!!, this also permit the use of the TUNE BUTTON on the flex without keying the amp. so my LDG automatic tuner work at low power, when antennas is tuned, you just press the pedal and adjust the load and plate of the amp. few second later you are good to go :-)

  • Nick
    Nick Member ✭✭

    is there really any advantage to buying an interface for the 811H? I can see needing an interface like the ARB704 mentioned above for old amps or radios, but my Flex 6500 is a modern radio and the 811H is even newer. Adding a 3-party amp is starting to sound like buying a new car. (Wheels and transmission sold separately). Apparently, I'd also have to buy an interface cable to go along with the interface. If the interface really adds value, I'll get one, but would like to hear from some others from the community that have experience adding non-flex amps.

    txn, Nick, KE5QY

  • WX7Y
    WX7Y Member ✭✭✭
    edited August 19

    Unlike the OLD TUBE AMP's that had about 170V on the AMP key line, The Amertron AMPs have much less voltage and current usually 12V DC and a LOW current of 100ma or so but it is a good idea to protect the AMP with a external transistor switching device like the ARB-704 but is it required. NO

    I myself would measure it with a Volt / AMP Meter and see for yourself how much current it takes to key the AMP and Voltage when it is a open circuit.

    Here is what Flex Radio says about the subject "https://www.flexradio.com/insider/using-external-amplifiers-with-a-flex-6000-transceiver-part-1/"

    "Open circuit voltage should not exceed +40 Volts DC. Closed-circuit current is 150 mA continuous max, and 500 mA peak max. There is the equivalent of a +45 Volt Zener across the output to ground that will clamp any positive-going transient peaks above +45 volts. Some older, and still popular TUBE amplifiers like Heathkits and the Kenwood TL-922, switch at a much higher voltage (on the order of -120vdc to -140vdc), some require a positive voltage and some even use 115vac with their relays. These types of amplifiers CANNOT be directly switched with FLEX-6000 radios and you will need to provide a keying buffer relay designed for the task. It is essential to check the manual of your amplifier to determine the keying voltage and current. A common solution that has been used by many FlexRadio users to the aforementioned issue with high voltages is to use a keying buffer relay like the ARB-704 amp to transceiver interface. It should be noted that some operators have opted to use a keying buffer with amps that have lower keying voltage lines as “insurance” to prevent any possible damage to the exciter due to possible transient voltage spikes or RF ingress."

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