4-47.3. LOUD HAILER - MAINTENANCE INSTRUCTIONS (Continued).
(2) Functional Sections.
(a) D.C. power circuits.
1 12 volt d.c. power is selected from either the internal or external batteries by the operation of
the toggle switch, S2, to the desired position. This does not apply d.c. power to the amplifier
however. The Press-to-Talk switch S1 supplies d.c. power to the amplifier only when it is
2 The current drain from the batteries is very small when S1 is closed and no signal is applied to
the microphone. The current is maximum when the loudest signal is being amplified, as the
collector current of the output stage varies with the strength of the amplified signal.
3 External battery power is obtained thru the receptacle J1 into which the external battery cable
is plugged. Both internal and external batteries furnish a nominal 12 volts. The dry cell
voltage will fall off with use while that from the storage battery will remain close to 12 volts
until the discharge state is approached. Somewhat greater power output at a given distortion
content is possible with the external storage battery, because the voltage remains more
constant and because the internal resistance is lower than that of the dry cell batteries.
(b) Battery cartridge or lung assembly. Eight D size cells (type BA-30) fit into the lung, four on
either side of the separator, on which outlines the cells shown the correct inserting position of each. The lung
cover assembly, contains a contact spring board, similar to that in the lung. This cover assembly is held to the
lung by four captive screws, with an "0" ring, in the joining surface to prevent entry of water. The upper leg of
the cover and the top leg of the lung are marked "TOP", as the cover assembly must be put on in this
orientation so that the cover contact springs will connect the battery cells correctly. In addition, the upper leg
on cover is longer than the other three, and the recess in the top leg of lung is correspondingly greater to aid in
orienting the cover properly.