Expo convertors with tubes ?

[Paul Perry]

At 01:16 AM 6/12/99 +0100, Rene Schmitz  wrote:

>I don't see how this tube could be used to build an expo convertor. 
>The QK329 has a square law. 
>
>However I could imagine that an exp (or log) law tube could be made using
>the same deflection principle. Replaceing that parabolic shape with an
>exponential one.
>
During the Heroic Age, people had oscilloscopes with a cardboard screen
stuck to the tube, cut in the shape of what transfer function they wanted
(log, square, Macdonalds arches, you name it).
They had a photocell looking at this, in a sealed box.
As the cro trace moved across, a feedback arrangement moved the spot up
and down so it rode on the edge of the screen.
And, looking at the Y signal, gave you the required.

paul perry melbourne australia