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 TM 55-1905-220-14-9
4-47.3. LOUD HAILER- MAINTENANCE INSTRUCTIONS
proportion of the sound energy fed back to the microphone so that in normal operating conditions in exterior
spaces, acoustic feedback is not a problem. The operator should be aware however that reflecting surfaces,
bulkheads, and the like tend to reduce this balancing effect against acoustic feedback.
(c) The microphone used in this loud hailer is magnetic type. A volume control is connected
between the microphone and the amplifier input for adjustment of the overall amplification of the system. The
amplifier is designed specifically for efficient transmission of speech and is a 3-stage transformer coupled
transistor type. The loudspeaker section consists of a semi-folded horn design which serves as an acoustic load
on the diver unit. The driver unit is a permanent magnet moving coil type with molded phenolic diaphragm.
(d) D.C. power from the self contained dry batteries in the center section of "lung" of the
loudspeaker horn is selected by operating a toggle switch in the base of the pistol grip handle to the proper
position. This power is switched on and off by a trigger switch located in the forward part of the handle. To
transfer the power supply from internal batteries to the external battery, the toggle switch is operated to the
"EXT" position. The power from the external battery is supplied through an external battery cable which is fitted
with a connector which mates with a receptacle in the bottom of the handle. The other end of the cable is fitted
with spring clips suitable for connecting to the terminals of a 12 v storage battery and fitted with rubber
insulating boots - red on the positive clip and black on the negative clip.
(e) The internal dry cell batteries also produce 12 volts when they are fresh. This voltage gradually
decreases with use, but the dry cells have sufficient capacity to furnish the equivalent of 2000 ten-second
messages before a lowering of output becomes unacceptable. From a practical standpoint they can be used
much longer depending upon how much decrease in output is considered tolerable by the user. The usable life
of these batteries is extended to the maximum if the trigger switch is never operated except when a message is
being delivered, and released immediately at the end of the message. Otherwise current is drawn from the
batteries unnecessarily, thus decreasing their life.
(f) Operation from the external storage battery is not as restrictive, as the battery can be
recharged when the voltage drops to the discharge value. The terminal voltage of a good storage battery also
remains more constant when a load is drawn, hence the available output of the loud hailer will always be close
to the maximum value when using an external storage battery, until the battery approaches the discharge state.
The output of the loud hailer will then start to fall off more rapidly than it does when the dry cell battery is
approaching the end of its capacity.
4-1194
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