audio input signals, regardless of what position the SELECTOR switch is in. Receiver audio
switches are designated 1, 2, 3, 4, 5, and AUX. Each receives audio from an associated
receiver. The NAV-1 and NAV-2 receivers are controlled by the NAV switch. The selected
signals are passed to the operator's headset through the mixing resistor networks, VOL control
R34, transformers T3 and T4, and headset amplifier AR2. The receiver switches allow
individual receiver monitoring or simultaneous monitoring of needed receivers at any time.
Direct input lines 3 and 4 and the interphone signal follow similar paths except that these
signals have no controlling monitor switches and are continuously and automatically
monitored. Direct input lines 1 and 2 follow similar paths except that they are applied directly
to T3 and are not controlled by the VOLUME control.
C-6533 circuit analysis. See subcourse foldout (FO-1).
Headset amplifier AR2.
Amplifier Q4 receives audio input signals from transformer T3 and provides an
amplified output which drives phase inverter Q5. Audio from direct input lines 1 and 2 is
applied to audio transformer T3 directly. All other audio inputs are applied to the arm of
VOLUME control R34 whose setting determines the signal level applied to transformer T3.
The output of the transformer secondary is applied to the base of amplifier Q4 through
coupling capacitor C12. Capacitors C13 and C29 provide low impedance paths to ground for
through collector load resistor R16. Resistor R14 provides a DC current path for emitter-to-
base bias. Capacitor C14 decouples the audio signals from the +20-volt supply. Negative
feedback from the push-pull output stage is applied to emitter resistor R15 from coupling
capacitor C19 and resistor R20. Negative feedback reduces distortion and maintains uniform
performance characteristics. The output signal for the amplifier is developed across load
resistor R16 and is applied to phase inverter Q5 through coupling capacitor C15. Capacitor
Phase inverter Q5 receives the audio output from amplifier Q4 and provides two
180-degree out-of-phase signals for application to push-pull amplifier Q6 and Q7. The output
of amplifier Q4 is applied to the base of Q5 through coupling capacitor C15. Resistors R18
and R19 determine base biasing, and capacitor C17 bypasses audio voltage from the power
source. Transistor Q5's current flows through the balanced collector/emitter load resistors R21