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High Voltage; X- And Y-axis Amplifiers; Z-axis Amplifier; Control Circuits - HP 1331A Operating And Service Manual

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(
(
Model 1331A
4-(i:J.
+
12.6 Regulator.
See
schematic 2.
A
sam-
ple
of
the output
of
the 12.6
volt
power
supply
is
selected and compared to a sample of
the
-50 volt
power
supply at
the base of A5Q4. Any
error (dif-
ference)
is amplified by A5Q4
and applied to
the base
of A5Q3. Series regulator Q4 is driven by A5Q3 in
such a
direction as to
correct
the
error.
4-64.
HIGH VOLTAGE POWER
SUPPLY.
4-65. See schematic
3.
When the instrument is first
turned on, Q5 starts to conduct through the primary
winding of A4Tl. Positive feedback to the base of
Q5
occurs
through the tertiary winding of A4Tl
and
the
circuit
oscillates
at a rate
determined· by the
distributed inductance
and capacitance
of the
cir-
cuit.
The conduction
angle of
Q5
(class C) and con-
sequently
the voltage
of
the
output,
is
controlled
by
the voltage at
the
collector of
A3Q2.
4-66.
A sample
of
the
+50
volt power
supply (selected
by A3R8) establishes
a
reference
at
the base of A3Q3.
A
sample
of the -2915 volt output
of
the high voltage
power
supply
is
fed
back to the ba..;e of A3Q3
and
compared
with the reference voltage. Any difference
(error)
is
amplified
by A3Q3
and A3Q2.
The
amplified
difference drives the base
of A3Q5
through the
tertiary
winding of
A4Tl in
such a
direction
as to
correct
the
error.
4-67.
The
oscillations are stepped
up by
A4Tl,
rectified by A4CR1
and
A4CR2, filtered by the
Rand
C components on
A4 and A3,
and applied as opera-
ting potentials to the
control
grid
and cathode of
the
CRT
write gun.
4-68.
The
output of the
gate
amplifier
is
connected
to the return
side of
the control
grid
supply. Any
variations in the
output
of the gate
amplifier,
varies
the total voltage on the control grid and
controls
the
brightness of the
CRT.
4-69. There
are
three inputs to the gate amplifier:
from the INTENSITY potentiometer, from the z-axis
amplifier (schematic
5),
and from the intensity
switch
(A5Q48/
A5Q49 on schematic
7).
The inputs
are
summed
and
the
composite signal
drives the gate
amplifier
to
control
the brightness
(or
blanking)
of
the
CRT.
A3Q9 and A3Q10
form a complementary am-
plifier. A3Q7
and
A3Q8
are
drivers for
A3Q9 and
A3Q10 respectively.
4-70. A portion
of
the
cathode
supply is tripled by
A 7 and provides the potential
for
the CRT post
accelerator.
4-71.
X-
AND Y-AXIS
AMPLIFIERS.
4-72.
See schematic 4. Because
the
x-
and
y-axis
amplifiers
are
nearly identical,
only
the y-axis am-
plifier will be
explained.
4-73. The
input
stage consists
of two
Darlington
pa
irs
(A5Q5A/
A5Q7 and
A5Q5B/
A5Q8) connected
as a differential emitter follower
pair. This
configura-
tion provides the required
high input impedance for
the
Y INPUT
and the current drive for
the
following
amplifiers.
4-74. Common emitter amplifier
A5Q9/
A5Q10 pro-
vides variable gain. Amplifier gain
is
controlled by
adjusting vert gain
potentiometer A5R38.
4-75.
The output
stage consists
of two
cascoded
pairs
(A5Q55A/
Ql4
and
A5Q55B/
Ql5)
connected as
a differential pair with a common current
source,
A5Ql3. This configuration provides the required
differential
drive
for the vertical deflection
plates
of the CRT.
Vertical position
control
is
accomplished
by
changing
the division
of current
through the two
halves
of the differential amplifier
when VERT POSI-
TION
control
R7 is
adjusted.
Compensation for
phase
shift (unequal output capacitance)
between
the
x-
and y-axis amplifiers is accomplished
by
adjusting
phase shift adj
A5Cl3. The
current
source for the
amplifier
is interrupted when BEAM FIND switch S3
is
activated.
This reduces
the gain and output
range
of
the
x- and y-axis amplifiers
to the point where
the
beam cannot
be deflected
off the CRT
screen.
4-76.
Z AXIS AMPLIFIER.
4-77. See schematic 5.
The
z-axis amplifier
increases
the
input
signal
to
a
level
capable of
driving the
in-
tensity gate which,
in
turn, drives the CRT write gun
control
grid.
The
z-axis amplifier
is
a
differential am-
plifier composed of
A5Q53
and
A5Q54.
Zener
diode
A5VR8
limits
the collector voltage of
A5Q53
to
8.25
volts;
this limits the power dissipated by A5Q53.
4-78.
CONTROL CIRCUITS.
4-79.
See schematic 6. The
control circuits consist
of the
ERASE switch, the STORE
switch,
and the
WRITE switch
on
switch
assembly
A8
and
the store
time adj circuits on
program board A6.
4-80. The ERASE switch is
a
spring-return push-
button switch. It will function only when the STORE
switch
is not
activated.
In WRITE mode, pressing the
ERASE switch applies
+158
volts
to the
erase
timing
a
nd storage
erase circuits on schematic
7. It also
applies +158
volts to the storage mesh of the CRT.
4-81.
The WRITE
and
STORE switches
are
push-
button
switches that are mechanically
connected
so
that
both
cannot
be activated
at
the same time. The
WRITE
switch,
when
activated,
interrupts the opera-
ting
current
to the inverter, A5Q35, on
schematic
7.
The STORE
switch,
when deactivated,
connects
the
PERSISTENCE
control
to
the
pulse generator on
schematic 7.
When activated, the STORE
switch
con-
nects the store time adj
control,
A6R2, to the pulse
generator.

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