Subcontractor.

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

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

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

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

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

Product Detector. The pcm signal inserted

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.

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