[Elecraft] Microphone Re-wiring Astatic D-104

[Ron D'Eau Claire]

First, may I suggest that you determine whether your D-104 already has that
amplifier. Later D-104s manufactured for solid state rigs had an FET amp
such as Don suggests built into the base. You turn the mic over and remove a
few screws to see if it has the amp. It uses a 9V battery that is in the
base as well. 

The earlier ones that O.T.s like Don and I remember, had no amp and were
used with the high-impedance (50K ohm to 100K ohm) input impedance of a
vacuum tube pre-amp. 

If yours has the amp, all you need do is put in a fresh battery and then
adjust the gain pot, which you will find in the base as well, for the
desired amount of gain. 

73, Ron AC7AC

-----Original Message-----

Alan,

The 4 pin vs. 8 pin is not your only problem. For pin to pin connections, I
suggest you consult G4WFW microphone connection database, it is quite
helpful.

The D-104 microphone element is quite high impedance, and some have
suggested simply using a series resistor to mitigate the high vs. low
resistance microphone impedance situation, I would suggest that a simple FET
stage could solve the problem.  The D-104 mic feeds the gate of the FET and
the output is taken from the source (or drain). There was a web reference to
the Heil FET amplifier that was recommended, but I have lost it.  I have it
on my hardrive and will send it to Alan in a separate email. -- the
reflector will not accept html nor any other resential

73,
Don W3FPR