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68813Re: Hardrock 50 driver amp relay question

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  • jim.veatch@verizon.net
    Sep 20, 2012
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      Hi John,

      The bias for the MOSFET should be a drain current of 500mA. In my experience you can't quite get there with 5V but 400-450 mA seems to work fine. In the Hardrock-50 a switched 5V source is supplier to the Driver PCB from the AMP PCB via the 'PWR' connector. If you are using the Driver PCB as a stand-alone amp you need some external way of putting 5V across VR201during TX.

      One way to do this is put a 5V zener across Pins 1 and 3 of VR201, (actually 5.1V) then add a series 1K resistor (R208) now you can supply a switched 12V source (which is what the relay needs too). I use a PNP switching transistor 2N3906 or similar which switches the 13V on to the relay and bias circuit by pulling it's base to ground through a 1K resistor (R209).

      I can't remember what like of TX signal the Softrock produces but may QRP rigs have an open contact pull ground arrangement for TX that will work with this circuitry.

      73's
      Jim WA2EUJ

      --- In softrock40@yahoogroups.com, John Williams <KE5SSH@...> wrote:
      >
      > Hi Jim,
      >
      > Can you explain the bias switching?
      >
      > John
      >
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