The Amateur Electrician: Build a Telephone (Dec, 1930)
The Amateur Electrician
Edited by THEODORE ALLEN
Experimenting with electricity is a most fascinating and instructive pastime. This month, Modern Mechanics and Inventions presents to its readers plans for making apparatus with which both the practical and theoretical side of electricity can be studied. Editors of this department always stand ready to assist readers in any way possible.
Talk to Your Friends Over These Simple Telephone Sets
RIGGING up a telephone connection with which you can talk back and forth to your neighbor at a distance up to a mile is an extremely easy matter. The only parts you need for each set is a transmitter, or microphone, and receiver, a Ford spark coil, a knife switch, and between two and five dry cells, depending upon the distance.
These parts are wired up with the circuit shown in drawing at the left. The microphone, dry cells, spark coil primary, and knife switch are all hooked in series to form the transmitting circuit of each set. One side of the spark coil secondary in each set is grounded to a water or gas pipe, or to any other firm ground connection. The other terminal of each coil is attached to the telephone receiver. Now to the free terminal of each of the telephones is fastened the wire which serves to hook up the two sets, this being the only connection between them.
For neatness sake the individual sets can be mounted on a board to look like the old fashioned wall telephone. The dry cells and coil should be placed in a small box which is fastened to the bottom of the board. Just above it is screwed the knife switch and the microphone. Several nails will hold the receiver.