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 TM 55-1905-219-14-9
4-46.3. LOUD HAILER - MAINTENANCE INSTRUCTIONS (Continued).
2
Volume control. Check tightness of the volume control knob set screw periodically, if the knob shows a
tendency to be loose, tighten the set screw.
3
External battery cable. Keep the external battery cable free of dirt and corrosion. The spring clips may
show a white deposit after being in use for some time. Clean this off with a knife or sandpaper and
apply a thin coat of petrolatum to reduce corrosive effects of battery electrolyte .
Also check the cord connector before use to be sure there is no dirt or foreign material blocking the
contacts.
c.
Principles of Operation.
(1)
Overall Functional Description.
(a) The loud hailer system is shown functionally in the block diagram. Briefly, the loud hailer consists of a
loudspeaker horn assembly bolted to the sound chamber body of the driver unit. The center section or lung of
the horn assembly is hollow, the interior containing eight flashlight batteries and means of making proper
connections to them. A watertight cylindrical housing with the amplifier assembly within it fits over the sound
chamber from the rear, and encloses the driver unit. The amplifier assembly is bolted into brackets at the base
of the housing, in such a manner that the power transistors are in thermal contact with the housing. The
volume control is mounted in the housing with its knob directly under the microphone enclosure. This
enclosure is a grilled cup which is secured by three screws to a bracket on the housing. The microphone
cartridge is supported on three cushioned studs and is held in place by a flange in the rubber mouthpiece,
which in turn is mounted in the front opening of the grilled enclosure.
(b) The pistol grip handle is secured under the center of balance of the assembly, by screws into both the
sound chamber body and into the horn. This handle houses the battery control switches referred to previously
and the external battery receptacle.
(c) The speech amplifier is a transistor amplifier, actuated by a microphone and driving a loudspeaker. Power
to energize the amplifier is derived either from an internal dry batteries or from an external battery, preferably a
12 volt storage battery. This power is controlled by the PRESS-TO-TALK trigger switch. Either power source is
selected by the INT-EXT battery selector switch. The amount of amplification of the speech signal from the
microphone is regulated by the VOLUME CONTROL.
4-1171
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