Re: {Collins} Astatic D-104

"The D-104 has a long history for use in a variety of commercial, amateur, and industrial settings and there is no reason for calumny by calling it a "CB Mic". That's almost as bad as referring to the early Neumanns with a separate capsule housing by the name of a long since deceased European dictator as is often done. "

Based on photos from 1930s Collins stations, the D104 was clearly the most popular mic used back then. Another popular mic with early Collins owners was the Shure 70 series. Both use piezo-crystal elements.

The D104 became popular with CB radio operators when the two-stage "power mic" circuit was added ca. 1968. The design of that circuit gets a solid "D" for performance. It uses a modified form of collector feedback bias and produces high levels of noise and harmonic distortion. It was supposedly designed as an active Z-matching transformer but when I computed the input Z, it is approx. 470K which is better than the low-Z termination of modern mic preamps, but a lot lower than the megohm range of a high-Z grid input. The output Z varies with the 5K-ohm level control.

Just a guess, but since the inception of Collins Radio in the early '30s, the D104 has likely been used more than any other microphone with Collins transmitters, especially during the three decade span prior to the introduction of the S/Line.

Paul, W9AC

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