contents - History of Ericsson - History of Ericsson

highest efficiency is obtained with the lowest possible weight of material.
Because of their high coercitive force, 250 pYsted, and the shape of magnet
adopted the magnets are resistant to demagnetizing to the highest degree,
both on short-circuiting of the magneto and with shocks and other mechanical
storain. The rotor is fully enclosed thus ensuring the highest reliability in
operation possible. The winding is completely insulated both from stator and
from rotor. There is consequently no risk of electric shocks from the metal
parts of the instrument. The load curve, Fig. 4, shows the given tension and
the power as functions of the external load resistance at 20 c/s. The maximum
power, 3.6 W, is higher than that attained with portable instruments of
earlier design.
The AC bell is of polarized type with magnet of 35 % cobalt steel and two
coils each with 500 ohm resistance, these being wound on bakelite. The gongs
are oval, stamped out of brass sheet. The sensitivity of the bell may be
adjusted by varying the armature gap width. Normally the bell is adjusted
to ring for a tension of 10 V.
The induction coil is made with closed lamellated core of siliceous alloy steelplate,
the mount and flanges being of bakelite.
The condenser has the duty of preventing the ringing current from passing
through the speaking device. Its capacity is 1 ^F and it is made for a test
tension of 500 V DC.
The battery has an EMF of 3 V and is made up of two standard rod cells
each of 1.5 V, placed in a common case measuring 36X68X85 mm. The
contact devices in the instrument are springcontacts. The battery is held in
place by a lid. The battery may be changed without the inset being taken from
the case. Ordinary round batteries may also be used in the instrument, a
special battery inset for the round batteries then being used.
In addition to the above-mentioned parts there are included with certain
types of instrument other parts as well, such as buzzer, dial, extra receiver etc.
The buzzer is used for voice-frequency telegraphy over distances greater than
those that can conveniently be covered by speech. By proper selection of the
contact material in the self-break contact and the introduction of a spark
quenching and noise reducing condenser of special type, sparking has been
to a large degree reduced. The buzzer is fitted in an accessible position on
a draw-out slide. The buzzer key is shaped with special regard to convenience
in use. In instruments fitted with buzzer there is in the lid above the key
a hole covered with a rubber-cloth membrane, allowing the key to be operated
while the lid is on.
The dial, which in instruments of this kind is a necessary accessory for connection
to automatic telephone networks, is watertight and provided with
rubber insulated connecting cable. When in use it is placed on the side of
the instrument by means of a special spring device, so designed that the instrument
lid may be put on even when the dial is to be used. For carrying,
the dial is placed in the free space at one end of the instrument.
The extra receiver is of new design and of special light-weight type. It is
fitted with rubber pad which considerably improves the fit to the ear. The
extra receiver is connected to the instrument by a rubber-insulated cable.
Types and Range of Application
In order to meet the varying demands made regarding the equipment of the
instrument and at the same time ensure the simplicity in operation it has
seemed advisable to introduce certain regular types intended for different
purposes.
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