[TenTec] Argonaut 509 sidetone "pop"

[Dr. Gerald N. Johnson]

On Fri, 2009-10-09 at 22:23 -0500, Ed - K9EW wrote:
> Hi Gil,
> 
> Yes, the T/R switching line in the 509 really wants to see a good
> solid ground for proper operation.  I've had to try various keyer
> output transistors to get decent operation.  No problem with a manual
> key.
> 
> I have heard of others with the same or similar problems, and the
> solution always seems to point to getting a very low voltage drop to
> ground for proper operation of the T/R line.  So I would suggest
> trying different transistors in the output of your keyer.

A power MOSFET (like the IRF-510, RS# 276-2072) with 5 to 10 volts of
gate drive will have a saturation voltage of less than 20 millivolts
while the bipolar will do hard to get that drop to less than half a
volt. Others are readily (at least from Mouser or Digikey, not RS) with
logic level rated gates will do that well with 2 to 5 volts of gate
drive. Hook a 10K resistor gate to source to turn them off good. And
maybe use a 10 (for logic level) or 15 volt (for others) zener diode to
protect the gate from static and other leakages.

And since the IRF-510 can be made to work as a RF amp to 50 MHz, it will
be fast enough for the keying circuit.
> 
> Let us know what you find.
> 
> 73,
> ed - k9ew
> www.k9ew.us

73, Jerry, K0CQ