[Boatanchors] WTB/WTT - High-Z PTT Desk Mike for HF SSB Rig

[Richard Knoppow]

    A couple of things, the shrill response of the D-104 is a design 
feature and was designed into the microphone to boost articulation in 
the presence of noise. It is mostly not an impedance effect but a matter 
of mechanical and acoustic resonances. The load impedance can roll the 
bass off even more than an "infinite" load will but is not the primary 
cause.
     The D-104 was the first crystal microphone to be offered 
commercially. Originally (1933) it was available in two versions, the 
familiar "shrill" version and a flat response version. The shrill 
version is the one that sold and survived. They worked well with 
transmitters with built-in speech clippers like the Johnson Valiant.
     The very high output level, about the highest of any commercial 
microphone, was a definite advantage in the days when electronic 
amplification was expensive. For the same reason crystal phonograph 
pickups became the defacto standard.
    Quite high-fidelity crystal microphones could be built, Brush made 
some "sound-cell" mics which used a stack of crystal elements without a 
diaphragm (sound acting directly on the crystals) which were used for 
acoustic measurement but they had quite low output.
    The biggest problem with all crystal elements is that they are very 
sensitive to high humidity, moderately high temperatures, mechanical 
shock, and fracture from overload when used as headphones or disc 
cutters. Ceramic elements are much less vulnerable but don't have the 
very high output. Crystal, ceramic and carbon have been virtually 
supplanted by electret mics.

On 8/16/2023 4:40 AM, Gary Peterson wrote:
> An unmodified, unamplified D-104 has too much output and greatly boosted high frequency response for most older SSB rigs.
> This requires the audio gain control to be set, barely above 8 o clock, making it difficult to adjust.  The D-104 was designed to drive a tube grid with a one megohm resistor as a load.  When connected to a much lower impedance, the D-104 has a rather shrill bump from 1.5 kHz and beyond.
> 
> Back when I ran a Kenwood TS-820S, I solved both problems.  I placed about a 700 or 800 kilohm, metal film resistor in series with the hot lead of the crystal cartridge.  I did this inside the push to talk base.
> 
> The resistor dropped the output sufficiently such that the mic gain control could be properly set to about 10 or 11 o clock.  The series resistor increased the load impedance on the cartridge and smoothed out the frequency response.
> 
> After the above mentioned modification, it was not unusual for other operators to ask me what radio and microphone I was using because they thought my audio sounded great.
> 
> Do not discount the venerable D-104.  As always, your mileage may vary.
> 
> Gary
> KzeroCX
> 
> “I have a couple of older tube-type SSB rigs, and I'm looking for a
> decent High-Z PTT desk mike.? I have a couple of Astatic D-104 mikes
> with the grip-to-talk stands, but I don't care for the D-104 sound on SSB.”
> ...
> ”If you have something that's surplus to your needs, I'd like to hear
> from you.? I'm willing to trade a D-104 or two if you have something I want.
> 
> Please let me know what you have (make & model).? A pic would be nice.
> 
> Thanks!
> 
> Mike Harmon, WB0LDJ”
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-- 
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998