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TM 11-5820-695-35
Q3. Resistors R12, R14, R15, and R19 are collector
and R27 through capacitor C11. C11 provides some
load resistors. When the signal at the base of Q2B goes
high frequency attenuation but it provides more low
more positive, the collector voltage goes negative and
frequency than is desired. To compensate for this, part
drives the base of Q3B negative. Conduction through
of the ig  (from R24) is coupled through low pass filter,
Q3B increases and charges capacitor C7.  When the
C10 and R30.
signal at the base of Q2A goes more positive, the
collector voltage goes negative and drives the base of
c.
Subcontractor.
Amplifier Al is a type
Q3A negative. The emitters of Q3A and Q3B are then
MC131G integrated circuit (fig. 5-24) which operates as
driven negative to reduce the charging current into
a unity gain differential amplifier. The input signal at pin
capacitor C7. The voltage across C7 is applied to Q4B
1 is the pcm signal. The input signal at pin 2 (inverting
and controls the gain of the age slicer.
input) is the pcm plus orderwire signal.  This signal,
FRPCM, comes through low pass filter, 'If, C23 and R45
g.
AF Amplifier. The orderwire plus residual
which eliminates frequencies above 50 kHz. The two
pcm output signal from subtractor Al is developed
pcm signals are as nearly equal as the circuits can make
across level adjustment potentiometer R34 and coupled
them.  The result is that the output signal is the
to the base of audio amplifier Q6. Transistor Q6 is a
orderwire signal plus some residual pcm because the
common emitter amplifier; dc bias is determined by
two pcm signals cancel (or the pcm at input pin 1 is
R36, RS7 and R34. Resistor R37 is bypassed for ac by
subtracted from the pcm input at pin 2).  The output
C16; R36 provides a small amount of degenerative
signal (orderwire plus residual pcm) is fed back through
feedback. Register R35 is the collector load resistor.
capacitor CS3 and resistor R6 to the primary of
The stage provides a gain of approximately 100. The
transformer T1.  It is also connected to the inverting
output signal is coupled through low pass filter C17,
input (pin 2) through resistor R31. Since the signal here
C18, and R38.  Transistor Q7 and Q8 are a power
is the pcm plus orderwire and the two orderwire signals
amplifier which provide current gain but no voltage gain;
are equal, the orderwire signal has no effect but the
the circuit operates essentially as an emitter follower.
residual  pcm  signal  provides  negative  feedback.
When the signal at the base of Q7 goes positive, current
Operating voltages are supplied to pin 1 through voltage
flow through emitter load resistor R39 increases and the
divider resistors R28 and R29 and to pin 2 through R33
emitter voltage increases. Increased current flow in Q7
and zener diode CR2. Capacitors C14 and C15 filter the
causes the voltage drop across the collector load, R41
supply voltages.
and R40 to increase.  This negative-going voltage,
tapped off at the junction of R41 and R40, increases
d
Buffer.
The  reshaped  pcm  signal,
current flow in Q8. This is the main source of signal
1RSPCM1, is passed through a low pass filter
current flow. The output signal is coupled through R42
composed of L1, R2, R3 and C1 with a cutoff frequency
and C20. R42 provides an output impedance of 100
of approximately 50 kHz. This passes the low frequency
ohms. Isolating resistor R46 connects the collector of
components of the pcm signal which is coupled through
Q8 to voltage check point E9.
buffer amplifier Q1 to pin 3-5 of transformer T1 with no
loss in signal.  Q1 is an emitter follower; dc bias is
h.
Level Detector.
The orderwire signal
determined by R3 and R4 and R4 is also the emitter
detector, comprised of C21, CR3, CR4, C22, R43, and
load resistor.  The output signal is coupled through
R44, is a voltage doubled-rectifier circuit used to
capacitor C2 and isolating resistor R6 to the secondary
monitor the peak amplitude of the radio recovered
of transformer T1.
orderwire
e.
Product Detector. The pcm signal inserted
i.
Voltage Filtering Components.
Voltage
at the transformer center tap and the feedback residual
filtering components ,I through L6 and C24 through CS1
pcm from the primary of transformer T1 are out of
limit the coupling of switching transients and other stray
phase in the secondary; cancellation by an amount
signals to the power supply circuits.
equal to the feedback pcm occurs. The resulting signal
(reduced pcm plus orderwire) is rectified and filtered by
C4, 05, R7, R8 and R9 and applied as positive dc pulses
to the bases of Q2A and Q2B.  Each half of the
secondary of transformer T1 works into a half wave
rectifier. Since their input signals are out of phase, the
output pluses at 4QA and Q2B alternate.
f.
Differential Amplifier.
The differential
amplifier operates as a class B push-pull amplifier.
Resistors R10, Rll, R47, and Rl1 set the dc bias level
for Q2 stages. The voltage is filtered by 06. Resistors
R12, R14, R16, R17, and R18 set the dc bias level for
2-85


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