Emilio Segrè Visual Archives

More than 30,000 photos of scientists and their work

Black Harold F1

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Black Harold F1

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Credit line: 
Bell Laboratories / Alcatel-Lucent USA Inc., courtesy AIP Emilio Segrè Visual Archives, Lillian Hoddeson Collection.

Photo of Harold Black on the inset. Photograph of Black's three-stage feedback amplifier. Embodying the principle of negative feedback, these amplifiers were first used in 1936 as repeaters in the coaxial cables between the cities of New York, NY and Philadelphia, PA. Negative feedback made it possible for each amplifier to carry 780 telephone messages simultaneously with great clarity.

Photo date: 
circa 1936
Original format: 
1 photographic print (black and white; 8 x 10 inches)
Black, Harold S., 1898-1983