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General Industries Carbon Microphone |
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| This double button carbon microphone was made by General Industries in the late 1920's. It is a large unit, measuring about 3 3/4 inches in diameter (not counting the spring hooks), and just over 1 1/2 inches thick. It is made from aluminum castings, so it is relatively light, at 1 1/2 lbs. It was advertised to have a frequency response of 30-7000 Hz, and was suitable for broadcast use. It was priced at about $70, so it was an expensive unit. |
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| The rear of the microphone has three concentric rings of screws. The outer ring (12 screws) holds the two halves of the microphone together. The two inner rings (8 and 4 screws) appear to be adjustments by which the diaphragm is tensioned to give the best frequency response. |
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| This microphone was marketed by E. F. Johnson as seen in this ad which appeared in March, 1929. Founded in 1923, E. F. Johnson started out as a mail-order distributor of radio parts and equipment. They grew to be a major manufacturer of high quality communications equipment and components for the professional and amateur user. Today, their focus is communications equipment and systems for law enforcement, fire-fighting, EMS, and the military. |