[Elecraft] Microphone Re-wiring Astatic D-104

[Joe Subich, W4TV]

> 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 Astatic amplifier uses bipolar transistors - not FETs.  There are
two issues with the stock amplifier ... it uses a 9V battery that does
not last very well and the gain level is rather high (it is very easy
to overdrive the mic input in any rig).  The schematic can be found 
here:  http://www.nucow.com/image/D104.jpg

73,

    ... Joe, W4TV


On 11/25/2012 11:21 PM, Ron D'Eau Claire wrote:
> 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
>
>
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