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Emerson Radio
attenuate the audio i - f . An overcoupled i-f (T4)
completes the amplifier stages and feeds the video
detector
(V4).
The audio level is maintained just below the
point of intertcrence with the video i-t. However,
the audio i-t is not completely rejected, as the audio
signal is recovered (ac the output ot the video de-
tector) by heterodyning with the video i-f.
The
4.5 me. beat between me video and audio inter-
mediate frequencies is obtained from the shunt-
tuned circuit consisting of L2 and C79 and is fed
to the first audio i-f amplifier (V7).
b.
VIDEO DETECTOR AND A.G.C. :The video
detector (V4A) rectifies the negative portion of
the video i-f.
The resultant signal is coupled
through peaking coil LI to the grid of the first
video amplifier ( V 5 ) . V5B acts as the automatic
gain control and develops a delayed negative A.G.C.
voltage which is used to bias the first two video
i-f stages and the r-f amplifier.
c.
VIDEO AMPLIFIER: The video amplifier con-
sists of two stages (V5 and V6A).
The second
stage is series-peaked and is coupled to the grid
of the kinescope (V25) and the sync separator
and d. c. restorer (VISA). The output signal of
V5 is varied by the CONTRAST control (R19)
which varies the bias of VS, to control the signal
input to V6A.
d.
D. C. RESTORER AND SYNC CLIPPER:
The output of the video detector contains both a.c.
and d.c. components of the video signal, as well
as the blanking and sync pulses.
Since the video
amplifiers will not pass the d.c. component of the
video signal, the background level of the picture
will vary.
The d.c. restorer (VISA) develops a
bias voltage across R24 which varies with the
average video signal level.
This bias voltage is
fed to the grid of the kinescope, thus maintaining
the proper brightness level. The video sync pulse
output of VISA, developed across R28, is coupled
through C22 to the first sync amplifier (V15B).
4.
DEFLECTION SECTION—The sync and sweep
stages produce and control the deflection of the elec-
tron beam in the kinescope. The horizontal sweep cir-
cuits incorporate a horizontal phase detector (sync
discriminator) to maintain automatic sync with the
horizontal pulses of the video signal.
a.
SYNC AMPLIFIER AND INVERTER: The
sync pulse output of VISA is amplified by two
triode stages (VISE and V6B) and fed to the
horizontal phase inverter (V11A). The integrat-
ing network of the vertical deflection circuit is
coupled to the output of VI1 A, which provides
push-pull' output for I'le horizontal sync discrimi-
nator ( V I 2 ) .
b.
HORIZONTAL SWEEP: The horizontal de-
flection circuits contain an automatic frequency
stabilizing arrangement which improves stability
and ease of operation. The phase inverter (V11A)
feeds the horizontal sync pulses to the horizontal
phase detector (V12).
At the same time, V12
receives voltages fed back from the horizontal out
put (V17) through CSS. Any phase shift between
the horizontal sync pulses and the horizontal os-
cillator signal will cause the input voltage applied
to one diode section of V12 to differ from that of
the other and result in a d.c. bias voltage on the
grid of the horizontal control tune ( V l l - b ) . This
bias voltage will be proportional to the phase dis-
placement between the incoming sync pulses and
the horizontal oscillator voltage and of a polarity
determined by the lead or lag of the oscillator fre-
quency.
The plate resistance of VHP) is part of
the bias network of the grid circuit of the horizon-
tal oscillator ( V l o ) . The output of the phase de-
tector (V12) will ihus synchronize the oscillator
to the horizontal pulses of the video signal.
The horizontal blocking oscillator (V13) operates
at a frequency determined by C57, R75, R76, and
the plate resistance of V I I B . The horizontal sync
pulses cause V13 to lock in at the sync frequency
when the HORIZONTAL HOLD control \R75)
is properly adjusted.
The sweep voltage output
of V13 is developed across R79 and is ted to the
horizontal output tube ( V I 7 ) .
The signal level
to the horizontal output tube is adjusted by the
HORIZONTAL DRIVE control, R80.
V19 supplies the required driving power for the
horizontal deflection coils (L9).
'ihe output of
V17 is coupled to the horizontal deflection coils
through output transformer T9. A portion of the
output transformer secondary is shunted by the
HORIZONTAL SIZE control L6.
By varying
the inductance of L6, the horizontal sweep current
may be controlled.
The horizontal damper tube (V19) acts to damp
out oscillations which occur over part of the hori-
zontal scanning cycle. The HORIZONTAL LIN-
EARITY control (L7)
helps provide a linear
trace.
V19 is a type 6W4 to eliminate the need
for a separate damper filament winding,
c.
VERTICAL SWEEP: Vertical oscillator V14 is
free-running and operates at a frequency determ-
ined by C71, R95, and the VERTICAL HOLD
control (R94), in the absence of a vertical sync
pulse.
The integrated sixty-cycle sync pulse de-
rived from the video signal reaches the grid of
V14 just before it would normally trip. This sync
pulse is great enough to drive the tube to conduc-
tion and cause it to lock-in at the sync frequency.
The sync pulse thus maintains control of the verti-
cal oscillator sweep frequency when R94 is cor-
rectly adjusted.
The output of V14 is fed to the vertical output
stage (V16) through C72.
The output of V14 is
controlled by the VERTICAL SIZE control
(R96).
R100 varies the operating point of V16
by varying the bias, acting as the VERTICAL
LINEARITY control The sweep voltage of V16
is coupled to the vertical deflection coils (L8) by
means of the vertical output transformer ( T i l ) .
5.
POWER SUPPLIES — Two power supplies are
used to supply the required voltages. The low voltage
supply uses a transformer and full-wave rectifier. The
high voltage supply for the kinescope is of the fly-back
lype and is energized by the horizontal output tube.
a.
HIGH VOLTAGE SUPPLY: The high voltage
power supply makes use of the energy supplied to
the horizontal output transformer by VI7. When
the plate current of VI7 is cut off at the instant
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