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 TM 55-1905-220-14-9
4-47.3. 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.
4-1199
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