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|  40. Rf Avc
the cathode of CR503, cut off the diode,
thereby clipping the peaks.
Rf avc gate CR505 functions the same as
39. If. Avc
the if. avc gate, except that the cathode is
connected through resistor R537 to a more
positive point on the detector load (junc-
a. During reception, approximately+5.6
tion of resistors R517 and R516). Thus, the
volts is applied to the cathode of detector
v o l t a g e that appears at the cathode of
C R 5 0 1 . This voltage obtainsd from the
C R 5 0 5 is always less negative than the
power supply, is applied through terminal
voltage at the cathode of CR504. This al-
4 of P509 and J509, and provides the delay
lows more delay for the rf avc bias and
action for application of avc voltage to the
i m p r o v e s the low-level signal sensitivity
i f . amplifiers.
of first and second rf amplifiers V102 and
b. The cathode of if. avc gate diode
V103. Resistor R537 and capacitor C526
CR504 is returned to the negative end of
filter rf and audio signals from the rf avc
the diode detector load (R516, R517, and
line. Resistor R533 is the rf avc load re-
R518). Diode CR504 cannot conduct until
sistor.
the algebraical sum of the +5.6 volts and
the negative voltage across the diode de-
tector load results in a net negative volt-
age at the cathode of CR504. When the in-
p u t signal amplitude causes the voltage
The audio signals developed across
a c r o s s R516, R517, and R518 to exceed
s e r i e s noise limiter load resistor R520
-5.6 volts, the cathode of if. avc gate diode
are coupled to the grid of first audio am-
C R 5 0 4 becomes negative, the diode con-
p l i f i e r V504 through coupling capacitor
ducts and develops a voltage across R531
C 5 2 2 . Resistors R514 and R525 form a
that is used as avc voltage for if. ampli-
voltage divider which decreases the ampli-
fiers V301, V302, V501, and V502.
tude of the input signals to decrease dis-
c. The exact voltage that causes CR504
t o r t i o n . Cathode resistor R526 is unby-
to conduct can be varied by the application
p a s s e d . This introduces degeneration in
of a negative voltage to the anode of CR504
the stage and reduces distortion that may
t h r o u g h R531. This voltage is obtained
be generated in the stage. Capacitor C516
from the squelch circuit (para 42) and is
i s a low-impedance path to ground for
also applied to the control grids of the if.
audio signals on the screen grid. On re-
amplifiers and controls the gain of these
ceive, plate and screen voltages are sup-
stages.
plied from the +125-volt dc supply through
relay contacts 12 and 20 of K601 (fig. 23),
d. The if. avc voltage is applied through
plate load resistor R527, and screen drop-
if. avc gate load resistor R531 and an audio
p i n g resistor R528. The audio output is
a n d rf filter consisting of resistor R530
developed across R527 and coupled to the
a n d capacitor C515. The if. avc bus is
g r i d of second receiver audio amplifier
decoupled from the diode load by resistor
V804 (para 43) through capacitor C517.
R529 and capacitor C514.
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