This circuit for P.A. it was found in a Radio Craft of January 1940, when this type of application was on the rise. The circuit sent the signal from a microphone to an amplifier that played it through a loudspeaker system. The circuit used 6 tubes and was powered by the mains. The oscillating coil determined the operating frequency, noting that in the original text there was already a restriction on the antenna so that the range did not exceed the FCC regulations.
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