68813Re: Hardrock 50 driver amp relay question
- Sep 20, 2012Hi 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.
--- In firstname.lastname@example.org, John Williams <KE5SSH@...> wrote:
> Hi Jim,
> Can you explain the bias switching?
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