Figure 7-17.--Test meter.

each amplifier. Normal operation of each stage will

amplifier channels and oscillator groups. Figure 7-17 is

an illustration of the test meter.

indicate a midscale reading (02 dB) on the meter.

Resistor R2101 is a potentiometer used to control

POWER RACK

the amplitude of the input signal being applied to V2103

and V2104. High-voltage switch S2101 is used to apply

The power rack (fig. 7-18) is a deck-mounted

plate power to the amplifier.

e n c l o s u r e that contains the two 500-watt,

audio-frequency power amplifiers and two ventilation

ADDITIONAL SOUND EQUIPMENT

blowers. The power switch for these blowers is located

on the control rack.

Additional sound equipment used with the system

The power amplifiers amplify the voice and alarm

includes (1) microphone control stations, (2)

signals received from their associated preamplifiers in

loudspeakers, (3) alarm contact makers, and (4) visual

the control rack and transmit the amplified signals back

alarm indicators.

to the control rack for further transmission to the

appropriate loudspeaker groups. The amplifiers

Microphone Control Stations

maintain a relatively constant output signal that is

independent of loudspeaker load. Therefore, impedance

The system has provisions for the connection of six

matching of the output is not critical, and adding or

type IC/MSB-2 microphone control stations. The

removing loudspeakers from the output of the amplifier

microphone control stations are installed at various

will have little or no noticeable effect on the output level.

locations aboard ship. The stations provide a means of

Figure 7-19 is a block diagram of a power amplifier.

transmitting voice announcements over the 1MC or

6MC circuits and select the loudspeaker groups over

Each power amplifier consists of two separate

which the announcements will be broadcast. All stations

chassis. Chassis 1 contains all the tubes and parts

are capable of transmitting over circuit 1MC. Only

required for actual amplification of the audio signals.

station 1 is capable of transmitting over both circuit

This chassis consists of an amplifier stage, a

1MC and circuit 6MC. Station 1 is normally located in

phase-inverter stage, two driver-amplifier stages, and a

the pilothouse/bridge and has operational priority over

final power-amplifier stage. Two parallel-connected

the other five stations. The other stations are normally

tubes comprise each stage except the final stage, which

located at the quarterdecks.

has six tubes in a push-pull parallel circuit. This parallel

connection of twin-triode tubes permits normal circuit

operation despite failure or removal of one tube per

stage or two tubes in the final stage.

Chassis 2 contains all the parts required to furnish

plate power to chassis 1. This chassis consists of a

plate-power transformer, high-voltage rectifiers,

low-voltage rectifers, and a filament transformer.

There are two eight-position selector switches and

two meters mounted on the front of the power rack, one

for each amplifier. These are used to check the operation

of each stage of the amplifiers and the signal output of

Figure 7-18.--Power rack.

Figure 7-17.--Test meter.

7-16