Carbon Microphone as a Crystal Radio Detector

A vintage telephone carbon microphone, which possesses multiple contacts between carbon granules and metal, was tried out as a detector, replacing the germanium transistor in my 
series-tuned, shunt fed crystal radio.

Vintage telephone carbon microphone

Series-tuned Shunt-fed Crystal Radio - Schematic
Its performance, after a bit of tapping, was as good as that of a razor blade detector (akin to moving the pencil or carbon contact on the razor blade to find the sweet spot).

Its performance improved considerably with a rundown button cell in series.

The carbon microphone behaviour was successfully simulated using two metal plates of size 8" x 8" x 1/16" with carbon granules salvaged from a discarded water filter.  

With one plate placed horizontally on the table, a thimbleful of carbon granules was distributed at the four corners and then sandwiched by the other plate. The top plate had to be moved to and fro to find the right spot.

During tests the signal strength was found to be fair with the specimen directly connected and very good with a rundown button cell connected in series with it.
_______________________________