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i t s grid rises to ground. When the COINCIDENCE SENSITIVITY
control is moved counterclockwise away from the NORMAL posi-
tion, the circuit is prepared for coincidence operation. During
coincidence operation, the same rapid rise of plate current in
V207A a s that produced by the early transition of the 3-1000-psec
gate must be obtained; thus fast triggers are necessary to operate
the coincidence circuit. Their duration i s relatively unimportant
but their rise time should exceed 0.2 p s e c over a 5-volt interval.
4.4.4 DELAY TRIGGER AND SYNC GENERATORS. The net-
work in the plate of V208A shapes the negative delayed trigger.
This pulse is amplified and inverted inV208B to form a positive
sync applied to V207B, the cathode-follower output stage. The
presence of the delayed sync a t the output terminal is indicated
by a stage comprising half of V104B. The positive delayed syn-
chronizing pulse causes this stage to draw grid current, charging
C251. The discharge of C251 through R279 in the time between
pulses keeps V104B off and causes V209, the DELAY MONI-
TOR lamp, to light.
proaches unity. The rising cathode voltage is coupled through
C330 and drives the cathode of D303 positive. D303 opens, and
the plate-timing networks for V303 are carried up along with the
cathode of V304. If the gain of V304 were exactly unity, a rise
of 1 volt a t the grid of V304
would cause the same rise a t the
cathode of V304 and an equivalent increase in B-plus, and the
current through the timing resistor would be constant. If this
happened, the sweep would be ideally linear. The small depar-
tures of the sweep with linearity are due to small departures
from a cathode-follower gain of unity. A very large resistance i s
thus needed in the cathode of V304 during the active portion of
this cycle. The linearly rising sweep voltage always attains an
amplitude of about 140 volts a t the grid of V306, the sweep am-
plitude comparator. The d-c reference voltage for this stage is
fixed to establish the correct sweep amplitude. When the sweep
h a s attained the 140-volt amplitude, V306 triggers, producing a
voltage rise a t the plate. This causes V305A to conduct, pro-
ducing the negative reset trigger that turns V302 off and V301
on. The sweep gate i s now reset to i t s normal condition. The
4.5
SWEEP CIRCUITS.
sweep generator is brought back into conduction, the keyed
4.5.1 GENERAL. The sweep circuits consist of a bistable con-
trol multivibrator, sweep generator, amplitude comparator, and
reset trigger amplifier. This loop is identical in configuration to
that in the delay circuits. The only difference is that the sweep
is generated by a bootstrap-type sweep circuit, which produces
a linearly rising sawtooth rather than the simple exponential
form produced in the delay circuits. The bootstrap-type sweep
generator produces a positive-going, linearly rising sawtooth,
which i s fed through a cathode follower to the positive sweep
output terminals, and from this cathode follower through an am-
plifier inverter to a negative-output cathode follower for t h e
negative phase. Also, a single-tube amplifier-inverter stage is
providedto produce negative and positive gates during the sweep
time.
4.5.2 SWEEP CONTROL GATE AND SWEEP GENERATOR. The
sweep gate multivibrator comprises V301 and V302 and their as-
sociated components. The low plate voltage of V301, which is
normally on, keeps V302 beyond cutoff. The plate voltage of
V302 is very nearly equal to the positive power supply voltage
(55 volts). Therefore, bothV303, the sweep generator, andV309,
the keyed clamp, are in conduction.
When a negative sweep trigger is received, V301 is turned
off and the resulting regenerative action causes V302 to switch
on rapidly. When V302 comes on, V303 and V309 are turned off,
and the sweep is started. Sweep timing
is
controlled by the r-c
"networks in the plate circuit of V303. Resistance
is
controlled
by S301, the SWEEP DURATION switch. Capacitance is con-
trolled by the SWEEP MULTIPLIER switch, S302. In Figure
5.3, the SWEEP MULTIPLIER switch is shown s e t to 1, the
SWEEP DURATION switch to 3 psec. Thus the sweep-timing
r-c network is C321, R323, and R329. Initially, with V303 in
zero-bias conduction, i t s plate voltage is very nearly a t ground.
The voltage a t grid 2 of V304A
is
low and i t s cathode voltage
is only slightly positive with respect to the grid. When V303
goes off, the selected sweep-range capacitor begins to charge
through i t s associated resistance network towards +300 volts.
The grid voltage of the cathode follower r i s e s and the cathode
follows. The cathode resistance of V304 with V309 off is very
high, s o that the gain of this stage a s a cathbde follower ap-
clamp is turned on, and the sweep-timing capacitor is discharged.
The conducting sweep generator can quickly reduce the voltage
across the sweep-timing capacitor to a small value, but the vol-
tage a t the cathode of the cathode follower, V304, must be re-
duced by the discharge of strays and by the replacement of
charge on the bootstrap coupling capacitor (C330) by V309. To
increase recovery time, this voltage must be brought back to i t s
quiescentvalue a s quickly a s possible; therefore, the plate cur-
rent of V309 is increased during the discharge period by V307A,
the reset cathode follower. The grid of V307A is driven positive
by differentiation of the negative sweep voltage a t V308B. This
voltage spike causes V307 to conduct, and momentarily in-
creases the screen voltage on V309, increasing i t s plate cur-
rent during the discharge interval.
T h e positive sweep a t the cathode of V304 is connected
t o the pulse-timing amplitude comparators to provide timing trig-
gers to start and stop the main pulse. V308A is the output cath-
ode follower for the positive sweep phase. Part of the positive
sweep voltage from the cathode of V308 is amplified and in-
verted by V307B, producing the negative sweep fed to the
SWEEP NEG output terminals through cathode follower V308B.
The trailing edge of the negative sweep drives the grid of
V310B through C331 to cause the spike of positive voltage a t
the grid of V310. Grid current charges C331, and the discharge
of C331 through R369 cuts V310B off. The rise in plate voltage
of V310B ionizes theSWEEP MONITOR lampV311 and indicates
the presence of the sweep a t the output terminal.
The grid of V305B
is
directly connected to the plate of
V301 and is thus positive during sweep time. The positive
sweep gate is present a t the cathode, and an equalnegative gate
is present a t the plate. This push-pull gate waveform is con-
nected through 1-pf coupling capacitors C339 and C338 to the
GATE output terminals on the panel.
4.5.3 SWEEP RESET SYSTEM AND SWEEP PROTECTIVE
CIRCUIT. The sweep-generating loop h a s the same monostable
characteristic a s the delay generating loop; that is, when the
gate is opened by the sweep trigger, the sweep rises until the
amplitude comparator triggers and feeds back a stop trigger to
close the gate. If, because of rapid warmup of V302 or simul-
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