On Feb 6, 2016, Jim Wilkins wrote
(in article ):

idwrote in
message ...
On 2016-02-06, Jim wrote:

I often look at all that stuff, and I find extreme ingenuity with
which people overcame limitations of their current technologies, it
is
fascinating.

i

Tbe one that impresses me most is the old analog telephone which does
everything over two wires without active electronics, only one very
clever transformer, speaker and carbon mike. I couldn't quickly find a
circuit description and should return to fixing my fallen TV antenna
that had me abseiling down the snow-covered roof.
Here is the core circuit of the pre-transistor circuit:

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

Joe Gwinn