Theory
ol Operation—465B Service
discharge rapidly
through Q7465 as pin
8
goes LO. C6121,
C6122,
C6112, R6115
and R6114
in the A and
B
Timing
Switch
circuit compose
the holdoff timing circuits
which
are
switch
selectable, and A Trigger HOLDOFF Rl4498is
a
variable resistor
that allows
lengthening
of
the time
constant to
increase holdoff time.
A Sweep Holdoff
Amplifier
The A Sweep Holdoff
Amplifier is Q7460. The holdoff
gate
waveform from pin 17 of U7375 is
applied tothe base
of
Q7460 through R7461
and
C7461.
When Q7460 is
turned off
(during holdoff
time),
its
collector is LO and
CR7451 is
forward biased, thus resetting both the Arm and
Firing
Trigger tunnel diodes in
the A Trigger
Generator.
When Q7460 is
turned on
(any time other than holdoff
time), its collector
level
is
HI and CR7451 is
reverse biased.
This allows the
trigger
tunnel
diodes in the
A Trigger
Generator to
respond to the next
adequate triggering
signal.
B Sweep
Holdoff Amplifier
The B Sweep Holdoff
Amplifier is Q7155. Its circuit
action is
identical
to
that described for the A Sweep
Holdoff Amplifier with the
exception that two gate
signal
sources
control the state of the stage.
The two sources are
the holdoff gate
from pin 17 of U7375
(through CR7363)
and
the collector of Q7075 in
the Delay Pickoff Com-
parator.
Both
gate
sources must be in their LO state for
B
Sweep to be
triggerable. Either source in its HI state
will
disable the B
Trigger Generator tunnel diodes.
A
Sweep Z-Axis
Gate
Q7181
and Q7182 comprise the
A Sweep Z-Axis Gate.
They form
an
emitter-coupled stage where only
one
transistor can be
conducting at any time. The
controlling
signals consist of inputs
from the collector of Q7254 inthe
A Sweep Gate, the
unblanking
signal
from
Q4582 in the A
Sweep
Generator, and Q4492 in the
Horizontal Display
Logic circuit. The
unblanking signal for use in the Z-Axis
Amplifier is
taken from the
collector
of Q7182
(through
CR7387). The
collector signal of Q7181 is applied
tothe A
+Gate Emitter
Follower
(Q7083).
The
Horizontal Display
Logic circuit
controls
the bias
voltage on CR7281.
When the
diode is
reverse biased, as
it
is
for all
horizontal modes except
for
B DLY’D,
-8
volts is
connected to
the anode of
CR7281 through Q4492.
This
allows the
gate signal at the
collector of Q7182 to pass
through CR7387
creating
the unblanking signal to
the
Z-
Axis Amplifier. In
the B DLY’D mode, Q4492
is turned off
and CR7281 is
forward biased
through R7281 to the +5
volts
supply. CR7387will now be reverse
biased, and the A
unblanking signal is blocked
from reaching the Z-Axis
Amplifier. In the
ALT Horizontal
Display mode, CR7281
will be
reverse biased during
the
A
sweep and
forward
biased during the B sweep.
B Sweep Z-Axis
Gate
The B
Sweep Z-Axis Gate is comprised of
Q7093 and
Q7095. These transistors
form an emitter-coupled stage
where
only one transistor can be
conducting
at
anytime.
The
controlling signals come from the collector of
Q7053
(B Sweep Gate),
and the blanking signal from
the collector
of
Q4562 in the B Sweep
Generator. The emitter current in
the gate
transistors is supplied
partly
by
Q7195 which is
controlled
by
B
INTENSITY control R14398. The B
INTENSITY control sets the
level
of
the
B Sweep
unblank-
ing signal to control the B
Sweep intensity separately
from
the overall display intensity. The
collector
of
Q7095
supplies the
unblanking signal tothe Z-Axis
amplifier and
the collector
of
Q7093 supplies the
signal to the B +Gate
Emitter Follower
(Q7092).
When
the A
Horizontal display is
selected,
-8
volts from
Q4491 in the Horizontal
Display
Logic circuit is
applied
to
the cathode
of CR7381. This reverse
biases CR7383 and
allows the collector of
Q7095 to be pulled positive
through
CR7385
and R7283
to
the
+5
volt supply. CR7386
will be
reverse biased
and the B Sweep Z-Axis Gate (Q7093
and
Q7095)
will
not
affect
crt unblanking.
When either A
INTEN, ALT,
or B
DLY'D
Horizontal Display is
selected,
-8
volts is
applied to the anode of CR7385 to
reverse bias it
and
allow the Horizontal Display Logic
circuit to control
the
B Sweep Z-Axis Gate.
In A Intensified
Horizontal Display, CR7381
becomes
reverse biased
and CR7383 becomes forward
biased.
Diode CR7386 is
still reverse biased, but
when B Sweep
starts,
the collector
of
Q7095 steps
negative enough to
forward bias CR7386
and
add a
slight amount of unblank-
ing to the
A Sweep
unblanking already present. This
provides further
intensification for the B Sweep
portion of
an A Intensified
display. In ALT
Horizontal Display,
the
Horizontal Display Logic
circuit controls the A
Sweep Z-
Axis Gate (Q7181
and Q7182) and the B
Sweep Z-Axis
Gate (Q7093
and
Q7095).
The B Sweep
unblanking signal
is added to the
A Sweep unblanking
signal during the A
Intensified
display, the A Sweep
unblanking signal is
blocked
during the B DLY'D display. In B
DLY'D Horizon-
tal Display,
the
A
Sweep Z-Axis Gate output
diode CR7387
is
held reverse biased,
and the only unblanking
signal
presented to the
Z-Axis amplifier input is the
B Sweep
unblanking signal.
A
+Gate and B -(-Gate
Emitter Followers
Emitter followers Q7083
and
Q7092
provide the
A
+Gate
and the
B
+Gate output
signals available at the
instrument rear panel.
The
output
signals are positive-
going
rectangular
waveforms, approximately +5.5
volts in
amplitude. The
amplitude is set
in
the
collectors of Q7181
and Q7093.
For example,
when
Q7181
is conducting,
the
base of Q7083
cangonomorenegativethan
approximate-
ly
-0.7
volt
(limited
by
CR7078).
When Q7181 is not
conducting,
the base of Q7083
rises tothe
+5
volts
power
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