Submitted by Bob Paquette
In 1915, General Electric organized a group of engineers under the direction of Ernst Alexanderson, to explore the possibility of radio broadcasting. Their early transmitters were high frequency alternators ranging in size from 2 kilowatts to 200 kilowatts. To modulate power in this range requires microphones of high current design.
The only microphones available were single button carbon transmitters used in telephone instruments. These microphones could handle about half an ampere, but not continuously. One logical step was to use multiple button microphones to handle the higher current draw. General Electric made three different models: a four button, six button and twelve button.
Alexanderson solved the high current microphone problem by designing a special transformer he called a magnetic amplifier or ‘magnetic modulator.’ This transformer, using magnetic core saturation principles and multiple cores, was capable of using a single telephone transmitter and a small direct current supply in the primary to control a very large radio frequency off the secondary. General Electric made various models of these modulators ranging from ten watts to seventy-five kilowatts.
In the early twenties vacuum tube circuits were replacing alternators, arc and spark equipment. They were now back to using the telephone transmitter as a microphone. They were no longer concerned with how much current the microphone could handle, but how they could improve the frequency response, distortion and noise characteristics?
General Electric’s first regularly operated station was WGY, which went on the air on February 20th, 1922. This gave the General Electric engineers a facility to test all their new apparatus including microphones. They immediately began to research microphones to see what type would be best suited for broadcasting. On July 25th, 1922, they started work on the condenser type microphone.
Meanwhile, Charles Hoxie, another General Electric engineer, was working on a device for the movie industry called a Pallophotophone. This was a combination microphone and film recorder. The microphone part of this device consisted of a mouth piece, diaphragm, mirror, light source, photo cell and amplifier. This became a working unit, but the microphone was not considered for further development. The word Pallophotophone (translated) meant “dancing light.” General Electric made a double button carbon microphone in 1923, but it was not considered for further development.
An experimental condenser microphone was used at WGY in August 1923, by June of 1925 General Electric engineers decided the condenser microphone was best suited for broadcasting and used their time to improve this type.
General Electric produced about 15 variations of their condenser microphones. The microphones were made between 1925 and 1928, and were of many shapes, based on what stage of development they were at when you ordered. Two variations were cylinder types with the microphone element in a swivel type yolk. These were made for the movie industry and hung by a bale off a boom stand. General Electric did not give them model numbers. A second to last model was referred to as the RCA 3A. This microphone was produced in a lager quantity than the rest. The last model was a three tube model in a six inch square box which was turned over to RCA in 1928 to manufacture. This became the RCA model 4A, the first microphone made by RCA.
General Electric had also produced experimental ribbon microphones in 1930. Their last model was very similar to RCA’s first ribbon microphone, the model PB17. Another microphone that should be mentioned is a crystal microphone made in 1926 for use with their sound meter.
A point of interest, RCA, up until 1929, was a sales organization. General Electric and Westinghouse owned shares in RCA. RCA was under contract to these two companies to sell their products. The agreement specified that RCA sales should consist of 60 percent General Electric products and 40 percent Westinghouse products. This is apparent in the radiola line and also in the broadcast equipment, including microphones.