On Mon, 14 Sep 2020, Frank Znidarsic wrote:

with this arrangement I can unplug them.  These earphones are of a 3000
ohm high impedance design.  The voice coil goes over a fixed magnet.  The magnet operates on a thin steel armature with no electrical connections on it.  The sound is very tinny and awfull  The Radiola III actually sounds much better with modern low impedance earphones.  

I wonder how those differed from earpieces in telephones of the time? Back then, everyone just took the "receiver" out of telephones.

See Nikola Tesla's 50-microvolt radio receiver pdf below. When actually built, it turned out to be an amplifier element, with multiple LC circuits giving it "regen" bias, plus even a local BFO oscillator so that CW Morse would be heard as beeps. The Corums measure its gain as orders better than any receiver before Armstrong's regen/superregen receivers.

  Tesla's receiver, a parametric amplifier, slow-rotating coherer

Tesla kept it secret, unpatented. The plans appeared in "Colorado Springs Notes" found in the 1970s. (The museum in Beograd had them, but wasn't releasing them until forced to publish, since the notes would harm Tesla's reputation of never taking notes, but only using his photographic memory! sheesh.)

There I am hoping to live to see the upcoming modern age of the low
impedance high fidelity loud speaker.

Try these 1925-era science-project magazine PDFs, with loudspeaker ads. (Note that some of those science projects appear to be "lost technology" which only appears in these pdfs, but weren't published in all the Popular Electronics or Scientific American project magazines. The "matter disintegrator" project, making weird carbon compounds from methane feed into a rotary spark-gap, probably was producing Fullerenes and diamonds in gram quantities!

  The Experimenter

  More, earlier:

When you find something like this from the incipient age of electrical
communication and get it working, you realize how short of a time that our
modern electrical age has existed.

Frank Znidarsic


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William J. Beaty                 https://electricatechnology.com
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