MAGNETO  WALL  PHONE  FROM  1907


 
THE B.-R. ELECTRIC & TELEPHONE MFG., KANSAS CITY, MISSOURI / USA (1907)
***********************************************************************
This telephone is over 100 years old and had a build-in battery. It has
a crankable generator ( "Magneto" ) to call the operator - or whatever
phone is on the other end of the wires ...

        

The original wiring of this Magneto Wall Phone was ...

    

To use this telephone today as a 2nd unit parallel to a dial phone,
it had to be rewired.  After trial-and-error the best results were
achieved with the following set-up ...

    

... using the original parts and adding two capacitors.  The "Magneto"
is connected to adjust the ringer by turning the crank in OFF position.

HOW THE RECEIVER WORKS:
=======================
This type of receiver is described in Bell's patent from 1877.  Two
coils of electromagnets are mounted on both poles of a long U-shaped
permanent magnet. With a small gap an unmagnetized circular diaphragm
lays over the poles. One coil of the electromagnet is wound clockwise,
the other is wound counter-clockwise. The AC of the voice signal, going
through the electromagnets, will either enhance or weeken the North
and South pole fields of the permanent magnet at the same time.  This
lets the diaphragm swing in frequency and amplitude of the voice signal.

    

HOW THE TRANSMITTER WORKS:
==========================
A small insulated cup has an electrode on its bottom and is filled with
carbon powder. The cup is covered with another, movable electrode which
is connected with a metal diaphragm. Activated by voice, air waves move
the diaphragm and its electrode more or less against the carbon powder.
Because pressed powder has a lower resistance,  the transmitter is a
variable resistor:  DC from a battery,  passing the powder,  will be
modulated in frequency and amplitude of the voice. This electric signal
goes over the wires to the receiver on the other end and restores the
voice. The star-like shape of the electrodes gives more surface area and
makes the microphone working independent from its orientation in space.

    

HOW THE DIAL SYSTEM WORKS:
==========================

    Have a look at chapter  » TELEPHONES & MULTIMETERS «  ...

HISTORICAL REMARKS:
===================

    Have a look at chapter  » TELEPHONES & MULTIMETERS «  ...

impressum:
***********************************************************************
© C.HAMANN      http://public.beuth-hochschule.de/~hamann      09/09/09