Audio Amplifier Module 1A2

C2, TM 11-6625-564-45

a. The 300-mc signal from uhf test gener-

1-19. Audio Amplifier Module 1A1

ator module 1A5 is applied to antenna jack J3

(fig. 4-8)

through DC1. The directional coupler con-

verts this 300-mc power to dc and applies it

The output of Handset H-101A/U is con-

to terminal 8 of TEST SELECT switch S1.

nected through HEADSET H-101A/U jack J4

to input transformer T1 of audio amplifier

When TEST SELECT switch S1 is set to

VSWR CAL, this voltage is applied to meter

module 1A1 and through coupling capacitor

Ml. This voltage is varied by VSWR CAL

C6 to the base of audio amplifier transistor

potentiometer R2 until meter M1 indicates

Q1. The signal is amplified and coupled suc-

cessively to succeeding stages Q1, Q2, and Q3

CAL.

b. The reflected power from the antenna

for increased amplification. Final voltage am-

plification stage Q 4 develops the audio output

applied to the coupler is also converted to dc

by the directional coupler. It is applied to ter-

across the primary of transformer T2. The

minal 9 of TEST SELECT switch S1. When

output of T2 is applied to both bases of

TEST SELECT switch S1 is set to VSWR

prower o u t p u t t r a n s i s t o r s Q 5 a n d Q 6 . T h i s

TEST, this voltage is applied to meter Ml

power output is developed on the primary of

for an indication of standing wave ratio (swr).

transformer T3 and supplied to the radio set

control for volume control and output

1-18. Audio Amplifier Module 1A2

through pins U and R of connector J2. Re-

(fig. 4-8)

sistors R5 and R14, R7 and R15, R9 and

R17, and R11 and R18 are used as voltage di-

An audio signal is supplied from the pilot's

viders to provide base bins for transistors Q1,

microphone (mike) output through pins E

Q3, QX and Q4, respectively. Resistors R24

and V of connector J2 of the radio set simula-

and R25 feed back avc voltages. which are

tor to terminals El and E2 of audio amplifier

tapped from the voltage-dividing networks

module 1A2.

This signal is then applied

formed by resistors R24 and R26, and R25

through input transformer T1 to AUDIO

and R27, to the emitters of amplifier transis-

GAIN potentiometer R23. AUDIO GAIN po-

tors Q1 and Q3. Feedback capacitor C5, con-

tentiometer R23 controls the volume by vary-

nected from the collector to the base of tran-

ing the amplitude of the input signal. This

sistor Q4, suppresses any high-frequrncy

controlled input signal is coupled through

noise applied to the base of Q.1. Resistor R30,

capacitor C1 to the base of audio amplifier

connected across the primary of transformer

transistor Q1.

The amplified output of Q1

T2. protects transistor Q4 from transient

is applied to the primary of transformer T2

voltages caused by the collapsing field around

and coupled by transformer T2 to the bases

transformer T2 when power is removed. Ca-

of power amplifier transistors Q2 and Q3. The

pacitors C1, C2, C3, and C4 are decoupling

power output of these two transistors is ap-

capacitors used with series resistors R1, R2,

plied to the primary of output transformer

and R3 to keep the audio stages from re-

T3 and coupled by T3 to HEADSET H-101

acting with each other. R e s i s t o r s R 1 2 a n d

A 17 jack J-4. The audio can be listened to

R13 feed back signals to the base of transistors

with a headset at this jack. Transient blanker

Q5 and Q6 that are 180 out of phase. This

module 1A4 supplies the +20 volts dc (para

feedback keeps the output constant.

1-14) for B+. Resistors R1 and R8 form a

voltage divider to provide base bias for tran-

1-20. Readout Mechanism

sistor Q1.

Resistors R3 and R11 are feed-

back resistors which reduce the effect of noise

(fig. 4-9)

in the power output circuit. Capacitor C3 in a

which

feedback

capacitor

suppresses

any

a. The readout mechanism indicates the fre-

high-frequency noise present. Resistor R4 and

quency selection made by a radio set control.

capacitor C3 form a negative feedback path to

The readout mechanism contains four Auto-

improve current stability.

positioners, each of which is attached to a dial