TM 11-6625-596-45
1A3T1.
Thus, it is possible to obtain a midscale deflection of
meter 1A4M1 in all three frequency bands regardless of
the shape of the frequency response characteristic of
2-3.
Noise Generator Assembly 1A3A3
the microphone or receiver being tested. The VALUE
controls are 1-dB per step ladder-type variable
attenuators.
Assembly 1A3A3 includes noise generator 1A3A3Q1
and amplifiers 1A3A3Q2 and Q3. Noise generator
h. Meter Amplifier. Meter amplifier 1A3A2
1A3A3Q1 is a germanium PNP type of transistor biased
raises the signals from the preamplifier and the
to operate in the high-noise region. Voltage divider
transmission efficiency circuits to a level adequate for
1A3A3R1 and R2, connected between the -12-volt
deflection of meter 1A4M1.
The mater amplifier
supply (pin P of 1A3A3P1) and ground (pin C of
includes a full-wave rectifier and logarithmic attenuator.
1A3A3P1), provides 1A3A3Q1 base bias current.
The output of the amplifier is a direct-current (dc) signal
Resistor 1A3A3R1 is the collector load, and emitter
proportional to the log-arithm of the alternating-current
resistor 1A3A3R5 provides negative dc feedback for
(ac) input signal. Therefore, the scale of 1A4M1 is a
temperature stabilization. Emitter capacitor 1A3A3C2
decibel scale during the earphone, microphone, sound
bypasses the emitter to ground for ac signals, providing
power telephone, telephone efficiency, and varistor
higher gain. The noise output of 1A3A3Q1 is coupled
tests.
through capacitor 1A3AC1 to the base of 1A3A3Q2.
Filter 1A3A3C3 and R4 isolate the-12-volt power source
i.
from 1A3A3Q1. Amplifiers 1A3A3Q2 and Q3 are
conventional common-emitter amplifiers. The coupling
electromechanical device which converts 100 volts
network (1A3A3C4, C5, C7, R10, and R11) between
direct current from the positive power supply to 20-Hertz
1A3A3Q2 and Q3 constitutes an equalizing net-work
square wave. The inverter output is applied to TEL
which insures that the amplitude of the noise signal
LINE terminals L1 and L2 through voltage divider
output is uniform with frequency. The output of 1A3A3
networks (part of 1A3A8) for the ringer and insulation
is applied through NOISE GENERATOR CALIBRATE
resistance tests.
control 1A4R12 to power amplifier assembly 1A3A4.
j.
Generator Test. Generator test assembly
2-4.
Power Amplifier 1A3A4
1A3A8 provides resistive loads and a full-wave rectifier
for the output of hand generators under test. The
rectified output of the hand generator is measured by
meter 1A4M1.
Assembly 1A3A4 is a transformer-coupled, 1-watt power
amplifier which includes amplifier 1A3A4Q1, push-pull
k. Dial Percent Break Test. Dial break test
driver 1A3A4Q2 and Q3, and output transformer
1A3A4T3. Amplifier A3A4Q1 is a conventional single-
assembly 1A3A9 contains circuitry to determine the
ended, common-emitter amplifier.
The output
of
make-to-break ratio of dial switches connected across
1A3A4Q1 is coupled through 1A3A4T1 to push-pull
the TEL LINE terminals. A free-running multivibrator,
driver 1A3A4Q2 and Q3. The output of the driver is
which generates simulated dial pulses used to calibrate
coupled through 1A3A4T2 and pins J, F, H, and K of
meter 1A4M1 for the dial speed test, is also located on
1A3A4P1 to power amplifiers 1A3Q1 and Q2.
1A3A9.
Thermistor 1A3A4RT2 and RT3 provide temperature
stabilization of 1A3Q1 and Q2. The output of 1A3Q1
l.
Dial Speed Test. Dial speed test circuit
and Q2 is coupled through output transformer 1A3A4TS
1A3A10 produces a direct current which is pro-portional
and pin B of 1A3A4P1 to acoustic output adjustment
to the speed of a telephone dial connected across the
1A3R11 and to NOISE GEN ADJ button 1A4S6A,
TEL LINE terminals.
Varistor button 1A4S6F, EARPHONES button 1A4S6G,
TELEPHONE EFFICIENCY-RECEIVE button 1A4S6P,
m. Power Supplies. Positive power supply
and TELEPHONE EFFICIENCY-SEND button 1A4S6R.
1A3A5 and negative power supply 1A3A6 convert the
Acoustical output adjustment 1A3R11 is adjusted (para
115/230-volt ac line voltage into the various dc voltages
required to operate the test set circuitry.
2
20 dynes/cm . Negative 30 volts is applied to assembly
1A3A4 at pin M of 1A3A4P1.
indicates when a resistance of less than 10 ohms is
connected across its terminals, it is not connected to
2-2
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