Re: How to explain how negative feedback lowers noise?

Tom Lee

Your comment about cathode resistors for bias stability will force me to do a little more background checking, but I don't think indirectly-heated cathodes were in production before 1929, so there could not have been cathode resistors for at least two years after Black. I did a quick perusal through a few schematics from that era, and I don't see cathode resistors of any kind showing up until around 1930 or 1931, and unbypassed ones don't show up for a couple of years after that. Blumlein doesn't invent the cathode follower until he starts working on radar on the eve of WWII. So my initial quick pass suggests that Black's invention does precede other forms of electronic negative feedback constructions. If you have earlier examples, I would be grateful to know about them. I'll look through other references in the meantime.


Sent from an iThing; please excuse the terseness and typos

On Mar 25, 2021, at 23:14, "Ed Breya via" <> wrote:

I don't know about this history, but am surprised that this didn't happen until 1929, well into the electronics era. Surely the concept of negative feedback in control systems has existed in nature, throughout human history, and in industry - at least since the steam era - look at the fly-ball governor, for example. Maybe in electronics, it wasn't so obvious, although it already existed in some forms, say for instance, with degenerative feedback in a vacuum tube, stabilizing the bias with the cathode resistor. People were driving horses, trains, planes, and automobiles successfully before 1929, using that PID controller in the skull.


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