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Krylon is a tough, quick -drying Acrylic
coating that has become a "must" in TV
service. Because of its high dielectric
strength it helps prevent corona. Spray
it on high voltage coil and insulation,
the socket of the high voltage rectifier
and component parts of the rectifier
circuit.
Krylon is nationally advertised.
CLEAR rustproofs,
waterproofs, insulates.Goes
on clear
and stays clear.
Vti
WHITE is popular for
touching up chipped
white good.
Will not discolor.
QED
ALUMINUM is nonconductive.
Protects
and insulates.
BLACK is newest
Krylon product.
Use for touch -up,
stenciling and
marking.
When a 6BN6 sync clipper with a
grounded cathode, using grid -leak bias,
is found, reducing grid -leak resistance
may', improve vertical synchronization
in weak signal areas (Fig. 8). The
resistor may be reduced from 1 megohm
to a value as low as 10,000 ohms,
provided no horizontal distortion, i.e.,
sync impairment, appears during the
reception of any channel. The output
of the separator is increased, since less
of the applied sync pulse is cut off.
Its separation action. however, may
be impaired, since video signals can
theoretically get through when the
signal input is not large enough to
drive the separator from zero bias to
well beyond cut -off. Since any video
signals that do get through will be
weak, they are not apt to noticeably
affect horizontal or vertical synchronization.
In any case, the subsequent
check for such impairment will show
whether the circuit change is acceptable
(Fig. 9).
In areas where the signal strength is
low, better reception may be obtained
with the contrast setting reduced, and
the brightness control setting advanced
(noise signals, or "snow" producers,
will not be amplified as much
under such conditions). Vertical retrace
lines may, however, be seen
(Fig. 10) when the brightness control
is moved beyond a certain point (below
the setting desired).
A circuit change to blank out the
CRT during vertical retrace time, and
thus eliminate the retrace lines, is il-
lustrated in Fig. 11A. The circuit
shown causes the relatively large voltage
pulses produced during vertical
sweep retrace time to be transferred
to the CRT cathode. If the correct
lead from the vertical output transformer
is attached to the CRT cathode
circuit, this voltage will be positive
during retrace time and will cause the
CRT bias to go beyond cut -off at this
time, blanking out all or most of the
retrace lines. The 27,000 ohm resistor
and .05 µfd. condenser integrate the
Fig. 9. When video signals get through the
sync separator. impaired interlace is apt
to result. Mottling of horizontal wedges
(moire effect) may be seen in such a case.
Fig. 10. Appearance of vertical retrace
lines may prevent desired advancement of
brightness control in the weak -signal areas.
vertical pulse, changing it to the
sharp -peaked type necessary.
Another circuit that can be used
for vertical retrace blanking is shown
in Fig. 11B. If the picture tends to
smear when a light background is
present in the televised scene, a 47,000
ohm resistor should be tried in place
of the 270,000 ohm unit. If a shaded
area at the top of the picture is always
present, reduce the value of the
.05 /Aid. condenser, in steps, to a capacitance
as low as .001 Afd. A third circuit
is illustrated in Fig. 11C. -3Ô-
Fig. 11. (A) Retrace line removal in a circuit similar to the General Electric 830.
Starred components were added. (B) Changes for vertical retrace line elimination in
an Admiral 21 series chassis. (C) Variation of the retrace elimination circuit shown
in (A). Starred components were added. The cathode of the CRT. which was originally
connected to the chassis, was opened and a 4700 ohm resistor inserted.
This resistor can be increased in value if any retrace lines remain visible. Circuit
is from an RCA Victor 630TS. converted to larger screen operation in accordance
with the suggestions made in General Electric's publication. "Techni- Talk."
TECHNICAL
CHARACTERISTICS
Dielectric constant -2.8
to 3.4 (1,000 cycles)
Dielectric strength -400
to 800 (number of volts
necessary to cause elec.
Inc arc through Krylon
coat one mil thick)
Electrical resistance -
lOta ohms /cmr
142
In U.S.A. and CANADA
SU TOUR JOBBER
Or Write Direst
Department 2704
KRYLON, Inc. 1/4
*CRY Lit SPIO
° er rNwhJNr
2601 N. Brood St., Philadelphia 32, Pa.
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