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Buffer/**** relay for keying


I want to use this simple circuit as a buffer/**** relay to key
my RF amplifier from the Flex 6300. I have used this many time before on
various rigs with success, but not the 6300. 

The relay will key when just the
tip of the RCA connector is inserted into the key jack on the 6300 on receive.

Is there a software setting I am missing that controls this? 


This circuit works
fine on my Elecraft K2.


  • Dennis Terry W4SG
    Dennis Terry W4SG Member ✭✭
    edited July 2019
    Perhaps it is just the wording you used but did you mean the key jack or the TX jack?  The TX jack  or the accessory TX pin is the proper one to connect to for what you are trying to do.  It needs to be enabled in the software transmit profile.  Not sure of the default state if it is not enabled.
  • Clay N9IO
    Clay N9IO Member ✭✭✭
    edited August 2019

    The TX jack is preferred and must be enabled in the menu under Transmit.

    It's good you're using a separate 12 volt supply.

    A more accepted practice if you must have an outboard relay for a dry pair is to introduce an NPN saturated transistor switch to buffer the current draw on your TX port. Very simple to build. For a transistor switch pretty much anyone will work.

    Curious what amplifier you are driving, many modern amps work perfectly with an RCA m-m cable from the 6300 to the amplifier. My Acom 1000 is one that does. When I had my L4B and TL922a I too built a transistor switch driven relay.
  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin
    edited April 2019
    I am curious as to why you need one as Clay asked?

    There is no need for one unless you are using a Heathkit amp or something like a TL922A.


  • aaron brio
    aaron brio Member
    edited April 2019
    Hi Mike....The 6300 only has one RCA jack to key an amplifier.  I would like to use a 4pdt relay to key other equipment in the shack.  
  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin
    edited July 2018
    Yep, that would be a good reason.   Make sure that you have that TX turned on as Clay mentioned.  It is off by default.


  • Neal Pollack, N6YFM
    Neal Pollack, N6YFM Member ✭✭
    edited July 2018
    Make sure that the current draw for the 4 pole relay coil does not exceed what the TX port on your 6300 can handle.  If unsure, or if it is near the limit, use a transistor to switch your relay coil.

    Here is a good primer on adding a transistor to switch the relay coil.
    You probably want PNP, so it turns on when the rig's TX output shorts to ground;

    But you might also want a capacitor to debounce the circuit, just be aware that this
    may add some delay in keying an amp, so you want to add a much smaller capacitor
    than they suggest in the below circuit, and you want to measure that switching delay
    with an oscilloscope and add some keying delay on your rig so you don't "Hot Switch"
    the amp;

    Again, if you find the specifications for how much current in milliamps that your Flex 6300
    can switch on the TX out port, and if your relay coil is less, you are fine without anything
    extra.   For me, just for added idiot proofing, I added an external key circuit like you want to,
    so I could key on multiple things like the amp, a transmit sign, etc.


  • Jlawson40
    Jlawson40 Member ✭✭
    edited March 2020
    Aaron, You can find the max current the TX port can sink in the Flex 6000 Harfdware Reference Manual. My 6600 max is 140ma. Not sure for the 6300. John
  • Greg N8GD
    Greg N8GD Member ✭✭
    edited July 2018
    The 6300 TX Output is also 140 mA @ +40 VDC maximum.  This is from the original FLEX-6000 Hardware Reference Manual, V1.2, dated 5/11/2014, which was published when the 6300 came out just prior to the 2014 Hamvention.
  • Roberto EA2CNU
    Roberto EA2CNU Member ✭✭
    edited August 2018
    These diagrams that I attach would be correct?
    The data of the solid state relay are:

    The data of the miniature relay are:

    Thank you very much for the help.

    Roberto EA2CNU

  • W2ENY
    W2ENY Member ✭✭
    Learned my lesson the hard way, keying a Henry amp with the TX RCA connector, had to send it back for repair, so I started building these, half the cost of the ameritron buffer relay and no 12v external supply needed.

    W2ENY - Flex 6300 HF Amplifier Buffer Relay Cable
    Buffer relay inside the Accessory (VGA) connector.


    73, Bob W2ENY
  • W2ENY
    W2ENY Member ✭✭

    Here's a pic of my cable's guts. 5V Relay and back-emf diode are all housed in the DB9 connector, I now have metalized version. I use alot of hot glue to keep things intact.

    Then make sure to switch it on in your settings.

    Sure beats the ameritron box and external 12v supply and all those cables..

    73, Bob W2ENY

  • Ned K1NJ
    Ned K1NJ Member ✭✭

    Had to comment.

    Great workmanship Bob!

    Really beautiful.

    Ned K1NJ

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