[Elecraft] D 104 mic with K2

[W3FPR - Don Wilhelm]

The D 104 mic (unamplified version) needs to look into a very high impedance
(50k ohms or greater).  That mic was developed in the days of vacuum tubes
with mic amplifier input inpedances in the 50k to 1 megohm range.

Modern transceivers present an impedance of something close ot 600 ohms at
the mic input jack, so to properly use a D 104 with modern transceivers, you
will need an amplifier stage - the gain can be low, but the input impedance
must be very high and the design output impedance should be in the vicinity
of 600 ohms.  A few circuits to do that have been published in QST over the
past 2 or 3 years.  Sorry, but I don't have a specific issue reference.

I took a different route with my D 104, I put a Heil HC-5 element in the D
104 head - it works FB, but the Heil elements need about 3 to 6 dB of gain
to properly drive the K2, so a preamp stage is still needed (or the KI6WX
increased gain mod of the KSB2 - which is what I use).

73,
Don W3FPR

> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net]On Behalf Of K9ut at aol.com
> Sent: Tuesday, September 27, 2005 7:39 PM
> To: elecraft at mailman.qth.net
> Subject: [Elecraft] D 104 mic with K2
>
>
> I would like to try the D 104 Mic. (crystal element )  in the K2 . I
> remember a circuit posted on the reflector on this , can anyone help ?
>
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>        Thanks ,72, 73,
>         Jerry Uhte K9UT K2  #  1273
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