1928

Harold S. Black applies for patent on his feedback amplifier invention.

1930

Harry Nyquist applies for patent on his regenerative amplifier (patent issued in 1933).

1937

U.S. Patent No. 2,102,671 issued to H.S. Black for "Wave Translation System."

B.D.H. Tellegen publishes a paper on feedback amplifiers, with attributions to H.S. Black and K. Posthumus.

Hendrick Bode files for an amplifier patent, issued in 1938.

1941

Stewart Miller publishes an article with techniques for high and stable gain with response to dc, introducing "cathode compensation."

Testing of prototype gun director system called the T10 using feedback amplifiers. This later leads to the M9, a weapon system instrumental in winning WWII.

Patent filed by Karl D. Swartzel Jr. of Bell Labs for a "Summing Amplifier," with a design that could well be the genesis of op amps. Patent not issued until 1946.

1946

George Philbrick founds company, George A. Philbrick Researches, Inc. (GAP/R). His work was instrumental in op amp development.

1947

Medal for Merit award given to Bell Labs's M9 designers Lovell, Parkinson, and Kuhn. Other contributors to this effort include Bode and Shannon.

Operational amplifiers first referred to by name in Ragazzini's key paper "Analysis of Problems in Dynamics by Electronic Circuits." It references the Bell Labs work on what became the M9 gun director, specifically referencing the op amp circuits used.

Bardeen, Brattain, and Shockley of Bell Labs discover the transistor effect.

1948

George A. Philbrick publishes article describing a single-tube circuit that performs some op amp functions.