Second 500-Kc If. Amplifier V502

+125-volt dc supply through the plate load

and R518. The audio signal is coupled from

w h i c h consists of rf choke L501 and re-

t h e junction of resistors R518 and R517

s i s t o r R504. Screen grid voltage is sup-

through resistor R538, diode CR503, and

capacitor C522 to the grid circuit of first

p l i e d through a voltage divider network

a u d i o amplifier V504. Capacitor C524

that consists of resistors R503 and R507.

grounds the cathode of detector CR501 for

C a p a c i t o r C519 decouples rf from the

audio and rf voltages. Resistor R538 and

+125-Volt dc supply. The output of V501 is

capacitor C521 filter rf components from

coupled through capacitor C502 to the grid

the audio signal. Jack J508 is a test point

of V502.

for measuring avc delay bias plus dc bias

d e v e l o p e d by detector CR501 across re-

35. Second 500-Kc If. Amplifier V502

s i s t o r s R516, R517, and R518. Resistor

(fig. 11)

R532 prevents test equipment from loading

The second 500-kc if. amplifier stage is

the detector circuit.

identical (except for reference symbols) to

c. The audio and dc voltage developed

first 500-if. amplifier V501 (para 34),

a c r o s s the diode load (R516, R517, and

and provides a second stage of amplifica-

R518) is also applied through resistor

t i o n to the 500-kc signal. The output is

R 5 1 5 to the control grid of squelch am-

coupled through C503 to the control grid

plifier V801 (para 42) and to the control

of V503.

grid of broadband cathode follower V802A

(para 63). The series circuit that consists

36. Third 500-Kc If. Amplifier V503

of capacitor C528 and L503 is resonant at

(fig. 11)

500 kc and provides a low-impedance path

The third 500-kc if. amplifier is similar

for the 500-kc if. components to ground.

to the two previous stages (para 34 and

35). Jack J505 is provided for injecting test

38. Series Noise Limiter CR503

signals for troubleshooting. Resistor R510

(fig. 12)

provides cathode bias for V503, and capac-

itor C509 is a bypass capacitor for rf.

a. The audio signal applied to the anode

C a p a c i t o r C506 is a low-impedance path

of diode CR503 is a varying dc negative

for rf signals between the screen grid and

w i t h respect to the cathode of detector

cathode. Plate voltage is supplied through

C R 5 0 1 . The applied signal is approxi-

resistor R512 and the primary of output

mately 63 percent of the total audio signal

transformer T501. Screen voltage is sup-

a c r o s s the diode detector load (resistors

p l i e d through voltage dropping resistor

R516, R517, and R518). The negative end

R511. Capacitors C527 and C510 and re-

of the diode detector load (junction of re-

sistor R512 decouple rf from the +125-volt

sistors R515, R516, R519, R529, and R532)

dc supply. The output of V503 is developed

is connected through a filter that consists

across the primary of output transformer

of capacitor C523, resistor R519, and

T501.

s e r i e s noise limiter diode load resistor

R520 to the cathode of diode CR503.

37. Detector CR501

b. T h e l o n g t i m e - c o n s t a n t o f r e s i s t o r

(fig. 12)

R519 and capacitor C523 causes a negative

bias voltage at the cathode of diode CR503

a. The secondary of transformer T501

that is fairly constant. This cathode volt-

is connected across detector diode CR501

age is more negative than the varying

through rf filter capacitor C520. Resistor

negative dc applied to the anode of CR503;

R539 is connected across the secondary of

the diode conducts and produces a voltage

T 5 0 1 to improve the frequency response

drop across load resistor R520 which re-

of the transformer.

produces the varying audio signal. Sharp

b. Detector CR501 demodulates the 500-

kc input and produces an audio signal

negative peaks of noise, which drive the

anode instantaneously more negative than

across detector load resistors R516, R517,