[Elecraft] D-104 Mic Element Replacement

[Gary Peterson]

If you have a working, unamplified D-104, the solution to this is quite simple.

Back in the 1990s, my transceiver was a TS-830S.  I had a pre-citizens band D-104.  These classic microphones were much heavier than the later ones and had a stamped serial number plate riveted to the head.

The output of these microphones was very high and, when connected to an input with an impedance of a few tens of thousands of ohms, the frequency response was very strident.  The Astatic data sheet for the D-104 contained a graph, with curves, which showed how a lower impedance load suppressed the mid range and bass response.  Inside the base of the push to talk stand, I placed a 787 kilohm,, quarter-watt, metal film resistor in series with the hot side of crystal cartrige output.  

The D-104 no longer sounded shrill.  The response was silky smooth, as determined by transmitting into a dummy load and recording the audio from a second transceiver.  As a bonus, I could then run my mic gain at eleven o clock, rather than nine o clock.  This made it much easier to set the mic gain properly, as the control was not so touchy.  

I was actively DXing, back then, and the slightly modified D-104 did a great job of breaking pileups.  I was often complimented on my audio and often asked what microphone I was using.

Gary, K0CX 

“Most D-104 mikes are not suited for use with today's radios.? The 
original D-104 was designed to work into a load impedance of 4 meg-ohms 
or higher.? Today's radios microphone input is about 50k ohms or so.?? 
The result is then excessive load on the D-104 element.? This is the 
major cause of frequency response issues.  Bob McGraw”

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