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I have a 6300 and will be using a Drake L7 do I need the ARB-704 and what pnp cable is used?

Drake L-7 hooked up to a 6300. Do I need the ARB-704 and what cable do I get?


  • Mike-VA3MWMike-VA3MW FlexRadio Employee, Community Manager admin
    edited April 2019
    Hi Don

    It would be good for you to actually take a voltmeter and measure the PTT keying voltage on the L7, or even check to see what it is in the manual.  I wasn't able to find it in the manual.

    Power up the Amp.  No need for the radio to be hooked up at all.

    Take a voltmeter and measure the voltage on the Amp key line.  I think it is about 28V based on Googling around.

    Now, put the meter in current mode and use both leads to short out the keying line and see what sort of current it draws.  It is likely around 100ma or so.

    If both numbers are less than what the radio can support, then you need a keying buffer.   Here is a good circuit.  http://www.ab4oj.com/dl/keyinterface.pdf


  • KC7ESKC7ES Member ✭✭
    edited November 2018
    If you do need an interface, I have an excess ARB 704. Just let me know. 73
  • Pat N6PATPat N6PAT Member ✭✭
    edited November 2018
    Why risk it? Just get the 704
  • Don StefanikDon Stefanik Member
    edited November 2018
    What pnp cable?
  • KC7ESKC7ES Member ✭✭
    edited November 2018
    Plug ‘n play ?
  • mikeatthebeach .mikeatthebeach . Member ✭✭
    edited November 2018
    Highly recommend these 3-500z amps have High voltage that can destroy switching circuits in flex and other solid state rigs
  • SteveSteve Member
    edited January 2019
    The 704 uses "rca" type cables and if I remember right it comes with a couple.  I also believe the "L7" uses rca type but I and sure it is in the manual or an online manual...73's
  • Brian Morgan VK7RRBrian Morgan VK7RR Member ✭✭
    edited December 2018
    Another issue is whether you intend to use high speed CW. A relay is too slow in switching for full QSK etc so beware that the circuit that Michael pointed you to, might not suit.  I use a solid state switch  because the speed is so much quicker than a relay. 

    Like many who have answered, I would not take the risk of damaging your Flex by trying direct switching. 
  • Doug HallDoug Hall Member ✭✭
    edited November 2018

    I highly recommend the W7RY QSK board for the Drake L7. Not only does it provide a soft keying circuit (safe for keying by any modern radio) it also gives you nearly silent T/R switching. Nice for CW or SSB VOX use.

    Note: It's not a kit -  you have to round up the parts (including a vacuum relay) and modify the L7 to install it, so if you are uncomfortable with equipment modifications then it might be better to simply buy a keying interface. But a QSK-modded L7 is a really sweet amplifier.

    Doug K4DSP

  • Don StefanikDon Stefanik Member
    edited November 2018
    Ok thanks everyone. When I had my TS-590 and a AL811 I had the ARB-704 but I had to have a special PNP cable to operate the 704. RCA cable to the amp.
     I have not been using a ARB-704 with my current AL80B and 6300 setup. 
    Also thanks KC7ES, but with the postal strike here in Canada shipping is a no go. I will just order one from DX Engineering which uses FedX to Canada and it's by far the least expensive  way for me to order stuff. I usually get it in 3 working days.

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