Capacitor C18 couples a degenerative feedback signal from the collector to the base of Q5.
The degenerative signal increases the audio bandwidth and decreases distortion. Output
signals at the collector and emitter of Q5 are applied to push-pull amplifier Q6 and Q7 through
coupling capacitors C20 and C21 respectively.
(3)
Push-pull amplifier Q6 and Q7 provides power amplification for application of the
audio to the headset. The two output signals from phase inverter Q5, 180 degrees out-of-
phase with each other, are respectively applied to the bases of Q6 and Q7 through coupling
capacitors C20 and C21. The input biasing network, for compensation of crossover distortion,
consists of resistors R23, R24, and R25 and diode CR7. The input signal is developed across
CR6 and CR8 for Q6 and Q7 respectively. The anodes of diodes CR6 and CR8 are biased at
a slightly positive potential by the input biasing network. Temperature compensation diode
CR7 provides the necessary transistor base/emitter bias over a range of temperatures. The
temperature compensation is necessary to assure the proper transistor operating point during
changes of transistor characteristics due to heat. Capacitor C22 eliminates high frequency
transients from the audio output. The audio signal is applied through output transformer T4 to
the headset. A portion of the output signal is fed back to amplifier Q4 through C19 and resistor
R20. The feedback signal is degenerative and reduces distortion.
b.
Microphone amplifier AR1.
(1)
Amplifier Q1 amplifies the microphone audio, and the resultant signal is applied
to amplifier Q2. The audio is applied to the base of Q1 through transformer (saturable reactor)
T1, coil L1 and coupling capacitor C1. Coil L1 and capacitor C25 form a radio frequency filter.
Capacitor C26 provides additional attenuation of radio frequency signals. The amplified output
signal is developed across collector load resistor R2. Resistors R3 and R6 are voltage
dropping resistors and resistor R1 provides a DC path for the biasing circuit. Capacitors C5
and C6 decouple the audio from the +20 V DC supply. Capacitors C2, C3, and C27 bypass
high frequency signals. The amplified signal is applied to amplifier Q2 through coupling
capacitor C4.
(2)
Amplifier Q2 amplifies the audio output of amplifier Q1 and the resultant signal is
applied to driver Q3. The signal is applied to the base of Q2 through coupling capacitor C4.
The amplified signal is developed across the collector load and is applied directly to driver Q3.
Resistor R4 provides a DC path for the base biasing circuit. Emitter resistor R7 provides
current stability.
8
Previous Page
