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The first Continental Electronics 317C 50kW AM transmitter was installed in 1965. The transmitter was mostly solid-state and featured few tubes, and it could deliver up to 125 percent positive modulation. The 317C offered motor-driven tuning and power adjustments, and was designed for unattended operation by remote control. A 12-phase plate power supply eliminated the need for a filter reactor and provided extra power for the high positive peak demands of low frequency programming. Continental Electronics manufactured the 317C until 1989, and there are still some in operation today.
That was then
The Altec 639A and 639B cardioid directional microphones were also sold under the Western Electric name, as shown in this ad from the October 1940 issue of Electronics magazine. The 639-type microphone combined a dynamic moving coil pressure element and a ribbon velocity actuated element enclosed in a housing that served as a protective guard and as a windscreen. The output of these two elements were used independently, or were combined in various proportions by means of a selector switch attached to the microphone to yield several directional patterns.
The 639A consisted of a ribbon velocity element and a dynamic pressure element, whose outputs are combined so that they yield a cardioid pattern. The 639B had a six-position switch that yielded omni, cardioid, several types of hypercardioid and figure-eight patterns.
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