U.S. Patent No. 2,102,671 - 2/21/1937 - Harold S. Black
Comments Concerning the Patent Gerald Stanley 03/03/2003: "Negative feedback amplifier. One of the most momentous inventions of our time, the negative feedback amplifier had much trouble getting a patent. Some very well educated "experts" who'd experienced feedback felt that it was not manageable as it would always lead to "singing" as they then spoke of oscillations. Black's invention was relegated to the same class as perpetual motion machines, of which the patent office had it's share of contributors. The final patent, as written, was used for training at Western Electric and is a model of clarity and clear thinking. Harold Black continued to make major contributions to amplification throughout his long and distinguished career. Today we also know him for having published extensively on the nature of pulse width modulation signals in his classic text Modulation Theory of 1953."