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Page Title: Figure 7-34.--Public address set, lecturn type.
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sound for entertainment or dissemination of
S2. Press-to-talk switch S1 supplies dc power to the
information. The set consists of an illuminated reading
amplifier only while the switch is held closed.
counter with a removable unidirectional dynamic
The current drain is very small when S1 is closed
microphone, a transistorized amplifier and controls, an
and no signal is applied to the microphone. The current
extended range loudspeaker, a battery meter, and jacks
is maximum when the loudest signal is being amplified,
for microphones, record player, tape recorder, and hvo
as the collector current of the output stage varies with
external speakers. Power to operate the set is provided
the strength of the amplified signal.
either by the self-contained dry battery, or an external
115-volt ac supply.
Microphone and Loudspeaker Assemblies
As an IC Electrician, you may be assigned the
The Mk 1 magnetic microphone has an impedance
responsibility for setting up and checking out public
of approximately 150 ohms. The microphone output is
address sets. To allow time for any minor adjustments
applied to transistor Q1 through volume control R1 and
or repairs that maybe required, always check the set or
capacitor C1. A selected portion of the sound radiated to
system well in advance of the time it is to be used.
the rear by the loudspeaker horn acts on the back of the
microphone diaphragm. This sound is phased so as to
reduce acoustic feedback
In this chapter, we have discussed how amplified
Loudspeaker LS1 is a moving-coil, permanent-
voice systems are used to amplify and transmit both
magnet type. Amplifier output signals actuate the voice
verbal announcements and alarm signals on board ship.
coil and diaphragm, and the resulting sound waves are
We have identified the various announcing systems by
amplified and directed by the loudspeaker horn.
their circuit designations.
We have explained how the various types of
amplified voice systems operate and how to maintain
Preventive maintenance consists of replacing
the systems. Also, we have described the additional
batteries, routine cleaning, and inspections. When the
sound equipment used with the systems and the
batteries are replaced, inspect the battery contact springs
procedures for maintaining this equipment.
and clean them if necessary. If the springs are badly
corroded, they should be replaced. Keep the external
power cable free of dirt and corrosion. Clean the spring
clips with sandpaper and apply a thin coat of petrolatum
to reduce corrosion. Inspect the connector and clean it
if necessary.
Periodically check the microphone housing. Keep
the opening to the microphone free of dust, dirt, oil,
grease, salt crystals, or other foreign matter. Salt crystals
left by the evaporation of salt water and spray should be
dissolved and rinsed away with fresh water, and then the
parts should be dried with a soft cloth.
Check the inside of the pistol-grip handle
occasionally. Remove the handle cover and inspect the
switch contacts. Clean if necessary.
The manufacturer's technical manual contains de-
tailed instructions for troubleshooting and repairing the
set. All components are designed for easy replacement.
Modern Navy ships are provided with the
lectern-type public address set. This set (fig, 7-34) is a
portable self-contained unit capable of reproducing
Figure 7-34.--Public address set, lecturn type.

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