Dual Magneto Telephone

The Phelps Dual Magneto Telephone

U.S. Patent 209289--October 22, 1878

This dual Magneto Telephone was intended to be used as a
transmitter. Phelps combines two or more diaphragms and
magnetic cores into one " volcalizing-chamber" to increase
the phone's output and to improve its articulation properties
as compared to a typical magneto phone. The magneto did
a satisfactory job working on short lines not subject to
interference. As the lines became longer, though, higher output
was needed. This design was able to achieve the maximum
output from a magneto telephone and was used as an alternative
to the carbon telephone transmitter.

The above photo courtesy of the Smithsonian Institution

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George M. Phelps