frequency and 1500 cycles per second for the high
SWITCHES.-- These switches provide power to the
frequency. In either case, clockwise rotation of the pots
two power supplies and relay power supply located in
will increase frequency and counterclockwise rotation
the control rack and the power amplifiers and blowers
will decrease frequency.
located in the power rack. During normal operation,
FLIGHT CRASH ALARM.-- The flight crash
these switches are in the ON position.
alarm consists of a phase shift oscillator that controls the
AMPLIFIER CHANNEL SELECTOR
frequency of a relaxation oscillator through a varistor
SWITCH.-- Three choices of channel operation are
network and an amplifier stage producing a siren tone.
available in this system: (1) 1MC-A/6MC-B, (2)
Figure 7-15 is a block diagram of a flight crash alarm
1MC-A/6MC-A, and (3) 1MC-B/6MC-B. Selection is
module. Operation of the flight crash alarm contact
accomplished by operation of the AMPLIFIER
maker supplies -30 volts dc through relay K501 to all
CHANNEL SELECTOR switch. Channel A is normally
stages of the circuit.
used for circuit 1MC operation, and channel B is
Resistor R7 (not shown) is a trimpot used in the
normally used for circuit 6MC operation. Should one
circuit to adjust the frequency limits of the siren tone.
channel fail during operation, the switch can be
Clockwise rotation of the pot will raise the frequency of
positioned to the operational channel, thus putting both
Q503, while counterclockwise rotation will decrease it.
circuit 1MC and circuit 6MC on the same charnel.
The normal setting produces a frequency varying
Under this condition, however, circuit 1MC has priority
between 750 cycles per second and 1750 cycles per
over circuit 6MC. Figure 7-16 is a simplified system
switching diagram showing the AMPLIFIER
CHANNEL SELECTOR switch in the 1MC-A/6MC-B
Switching and Transfer Controls and
OSCILLATOR GROUP SELECTOR
SWITCH.-- Selection of either group of alarms is
accomplished by operation of the OSCILLATOR
The switching and transfer controls on the front of
GROUP SELECTOR switch. Should any alarm module
the control rack consist of the amplifier oscillator power
within either oscillator group fail during operation, the
switches, the amplifier channel selector switch, the
switch can be positioned to the operational group.
oscillator group selector switch, the microphone control
During normal operation, this switch is in the NO. 1
station disconnect switches, the loudspeaker group
disconnect switches, visual disc switch, and various test
M I C R O P H O N E CONTROL STATION
switches. Indicators on the front of the control rack
DISCONNECT SWITCHES.-- There are six mi-
consist of a power available lamp, blown-fuse
indicators, and a test meter.
crophone control station disconnect switches, one for
Figure 7-15.--Block diagram of the flight crash alarm module.