As a precautionary rule, whenever you reach a point in the sync separator
system where the injected pulses do not lock in the picture, try both polarity
pulses. If you find that one polarity of sync pulse does lock in the picture,
the stage is operating satisfactorily.
Within the past few years pentagrid tubes have been employed for the sync
separating function, at the same time also helping to reduce the amplitude
FROM
VIDEO
SYSTEM
SYNC. AMP.
6CB6
::- +130V
265V
SYNC. SEP.
6AU6
lJl][
20V.P-P
\
s1Nc. AMP.,,.,..-Jlll SOV.P-P
z6BF6 {4.7K
.01
.047
�OVERT.
SYSTEM
4.7K
6.8
8 2
K
T
MMF +130
130V
265V
TO HORIZ,
SYSTEM
Figure 9-A more elaborate sync separator system
of any noise pulses that may be riding along with the signal. A typical cir
cuit of this type is shown in Fig. 10. There is a 6BY6 pentagrid tube followed
by a triode sync amplifier. A fairly small video signal with the sync pulses
negative is fed to grid No. 1. The sync stabilizer control connected to the
grid is adjusted so that tube current just flows with normal input signals.
An amplified version of the same video signal, with the sync pulses posi
tive now, is obtained from the plate of the video amplifier and applied to
grid No. 3 of the 6BY6. These sync pulses are strong enough to cause grid
currents to flow in this circuit, charging capacitor Cl to a value approxi
mately equal to the peak-to-peak amplitude of the applied pulses. In the inter
val between pulses, the negative voltage on grid No. 3 is high enough to pre-
FROM
VI O EO _ _.,.,,......,.-+---t+
DET.
270
SYNC SEP.
6BY6
820
K
27 K
I MEG
SYNC.
K
.047
I_
135V
STABILIZER
..,_
-cc"'
CONTROL"
• ....
,......-IWv--135V
2.5M
Figure 10
SYNC AMP.
½6AN8 6.8K
47
K
22K
TO VERT.
�--.,.,....,.,,.-•SYSTEM
4.7
K
18
MMFT
135V
TO HORIZ.
SYSTEM
Sync Separator System
vent current from flowing through the tube. Thus, when the circuit is operat
ing normally and a video signal is received, current will flow through the
6BY6 only during the sync pulse interval and only sync pulses will appear
across the output load resistor.
21
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