Emerson R adio
attenuate the audio i-f. An overcoupled i-f (T4)
completes the amplifier sta es and feeds the video
detector (V4).
The audio level is maintained just below the
point of interference with the video i-f. However,
the audio i-f is not completely rejected, as the audio
si nal is recovered (at the output ot the video de
tector) by heterodynin with the video i-f. The
4.5 me. beat between the video and audio inter
mediate frequencies is obtained from the shunt-
tuned circuit consistin 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 ne ative portion of
the video i-f. The resultant si nal is coupled
throu h peakin coil LI to the rid of the first
video amplifier (V5). V5B acts as the automatic
ain control and develops a delayed ne ative A.G.C.
volta e which is used to bias the first two video
i-f sta es and the r-f amplifier.
c. VIDEO AMPLIFIER: The video amplifier con
sists of two sta es (V5 and V6A). The second
sta e is series-peaked and is coupled to the rid
of the kinescope (V25) and the sync separator
and d. c. restorer (V I5A). The output si nal of
V5 is varied by the CONTRAST control (R19)
which varies the bias of V5, to control the si nal
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 si nal, as well
as the blankin and sync pulses. Since the video
amplifiers will not pass the d.c. component of the
video si nal, the back round level of the picture
will vary. The d.c. restorer (VI5A) develops a
bias volta e across R24 which varies with the
avera e video si nal level. This bias volta e is
fed to the rid of the kinescope, thus maintainin
the proper bri htness level. The video sync pulse
output of VI5A, developed across R28, is coupled
throu h C22 to the first sync amplifier (V15B).
4. DEFLECTION SECTION—The sync and sweep
sta es 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 si nal.
a. SYNC AMPLIFIER AND INVERTER: The
sync pulse output of V I5A is amplified by two
triode sta es (V15B and V6B) and fed to the
horizontal phase inverter (VI1A). ^he inte rat
in network of the vertical deflection circuit is
coupled to the output of V I1 A, which provides
push-pull output for the horizontal sync discrimi
nator (V12).
b. HORIZONTAL SWEEP: The horizontal de
flection circuits contain an automatic frequency
stabilizin arran ement which improves stability
and ease of operation. The phase inverter (V I1 A)
feeds the horizontal sync pulses to the horizontal
phase detector (V12). At the same time, V12
receives volta es fed back from the horizontal out
put (V17) throu h C58. Any phase shift between
the horizontal sync pulses and the horizontal os
cillator si nal will cause the input volta e applied
to one diode section of V12 to differ from that of
the other and result in a d.c. bias volta e on the
rid of the horizontal control tuoe (V Ilb ). This
bias volta e will be proportional to the phase dis
placement between the incomin sync pulses and
the horizontal oscillator volta e and of a polarity
determined by the lead or la of the oscillator fre
quency. The plate resistance of VIIB is part of
the bias network of the rid circuit of the horizon
tal oscillator (VlJ). The output of the phase de
tector (V12) will thus synchronize the oscillator
to the horizontal pulses of the video si nal.
The horizontal blockin oscillator (V I3) operates
at a. frequency determined by C57, R75, R76, and
the plate resistance of VIIB. The horizontal sync
pulses cause V13 to lock in at the sync irequency
when the HORIZONTAL HOLD control (R75)
is properly adjusted. The sweep volta e output
of V13 is developed across R79 and is ted to the
horizontal output tube (V I7). The si nal level
to the horizontal output tube is adjusted by the
HORIZONTAL DRIVE control, R80.
V19 supplies the required drivin power for the
horizontal deflection coils (L9). ihe output of
V17 is coupled to the horizontal deflection coils
throu h output transformer T9. A portion of the
output transformer secondary is shunted by the
HORIZONTAL SIZE control L6. By varyin
the inductance of L6, the horizontal sweep current
may be controlled.
The horizontal damper tube (V I9) acts to damp
out oscillations which occur over part of the hori
zontal scannin 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 windin ,
c. VERTICAL SWEEP: Vertical oscillator V14 is
free-runn.n 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 inte rated sixty-cycle sync pulse de
rived from the video si nal reaches the rid of
V14 just before it would normally trip. This sync
pulse is reat enou h 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 outptu
sta e (V16) throu h C72. The output of V14 is
controlled by the VERTICAL SIZE control
(R96). R100 varies the operatin point of V16
by varyin the bias, actin as the VERTICAL
LINEARITY control. The sweep volta e of V16
is coupled to the vertical deflection coils (L8) by
means of the vertical output transformer (T il).
5. POWER SUPPLIES — Two power supplies are
used to supply the required volta es. The low volta e
supply uses a transformer and full-wave rectifier* The
hi h volta e supply for the kinescope is of the fly-back
lype and is ener ized by the horizontal output tube,
a. HIGH VOLTAGE SUPPLY: The hi h volta e
power supply makes use of the ener y supplied to
th$ horizontal output transformer by VI7. When
the plate current of V I7 is cut off at the instant
Scanned by mbear2k - Jan 20121/17
