wikipedia https://en.wikipedia.org/wiki/Negative_feedback

Description of the ‘flash of realisation’ of the breakthrough

Click to access 06501721.pdf

Ronald Kline telling the same story

Click to access FBBlack.pdf

Oral history: interview

https://ethw.org/Oral-History:Harold_S._Black

Black’s 1934 article in The Bell System Technical Journal

Click to access Black.pdf

Alternative link for video https://www.youtube.com/watch?app=desktop&v=iFrxyJAtJ7U

Harold Black and the Invention of the Negative Feedback Amplifier

Harold Black and the Invention of the Negative Feedback Amplifier – AT&T Archives – YouTube