V962 are replaced
by
silicon high-voltage rectifier diodes
D951
and
D961
and there
is
no further need
for
the windings
that provided filament voltage to the rectifier tubes. An ad-
ditional
low-voltage
winding
provides the filament voltage
for
the cathode-ray tube.
Positive accelerating potential
is
supplied
by
voltage
doubler
D951
and
D961
(V952 and V962
below
serial num-
ber 44360). Regulated voltage output
is
about
+8
kilovolts.
Ground return
for
this supply
is
through the resistive helix
inside the cathode-ray tube to pin 7 and then to ground
through
R972.
The negative accelerating potential
for
the
CRT
cathode
is
supplied
by
the half-wave rectifier D952.
Voltage
output
is
about
-1.95
kilovolts. A sample
of
this output voltage
is
connected to the High-Voltage Regulator stage to provide a
regulated high-voltage output.
The half-wave rectifier D940 provides a negative voltage
for
the control
grid
of
the
CRT.
Output
level
is
adjustable
by
R940,
CRT
Grid
Bias
adjustment.
The
neon bulbs 8973,
897 4 and 8975 provide protection
if
the voltage difference
between the control
grid
and cathode exceeds
about
165
volts.
The
unblanking
gate
from the Z Axis
Amplifier
is
applied
to the positive side
of
this circuit to produce a
change in output voltage to control
CRT
intensity, unblank-
ing, dual-trace blanking and intensity modulation.
CRT
Control
Circuits
Focus
of
the
CRT
display
is
controlled
by
the FOCUS con-
trol,
R967.
Divider
R963-R968
is
connected between the
CRT
cathode supply and ground.
The
voltage
applied
to the
focus
grid
is
more positive (closer to ground level) than the
voltage on either the control
grid
or
the
CRT
cathode.
The
ASTIG adjustment,
R985,
which
is
used
in
conjunction with
the FOCUS control to provide a well-defined display, varies
the positive level on the astigmatism grid.
The
+90-volt
source for this control
is
provided
by
zener
diode
Dl043
in
the Z Axis
Amplifier
circuit.
Geometry adjustment,
R982,
varies the positive level on
the horizontal deflection plate shields to control the overall
geometry
of
the display. Two adjustments control the trace
alignment
by'
varying the magnetic fields around the
CRT.
The
Y Axis Align adjustment,
R989,
controls the current
through
L989
which affects the
CRT
beam
after
vertical de-
flection but before horizontal deflection.
The
TRACE
ROT
A-
TION
adjustment,
R980,
controls the current through
L980
and affects both vertical and horizontal rotation
of
the beam.
External Z Axis Input
A signal applied to the Z
AXIS
INPUT connector
(see
Z
Axis
Amplifier
schematic)
is
applied
to the
CRT
cathode
through C979-C976-R976.
DC
and
low
frequency Z-axis sig-
nals are blocked from the
CRT
circuit by C979. They are
connected to the Z Axis
Amplifier
circuit to produce an in-
crease
or
decrease
in
intensity, depending upon polarity.
C976 and C979 couple high-frequency signals directly to the
CRT
cathode to produce the same resultant display
as
the
Z Axis
Amplifier
circuit produces
for
low-frequency signals.
®
Circuit
Description-Type
453/R453
This configuration operates
as
a crossover network to provide
nearly constant intensity modulation from DC
to
50 mega-
hertz.
LOW-VOLTAGE POWER
SUPPLY
General
The
low-voltage
Power Supply circuit provides the operat-
ing
power
for
this instrument from three regulated supplies
and one unregulated supply. Electronic regulation
11
is
used
to provide stable, low-ripple output voltages.
Each
regulated
supply contains a short-protection circuit to prevent instru-
ment damage
if
a supply
is
inadvertently shorted to ground.
The
Power Input stage includes the Line Voltage Selector
assembly.
This
assembly allows selection
of
the nominal
operating
voltage
and regulating range
for
the instrument.
Fig. 3-17 shows a detailed block
diagram
of
the Power
Supply circuit. A schematic
of
this circuit
is
shown on
dia-
gram 17
at
the rear
of
this manual.
Power Input
Power
is
applied
to the primary
of
transformer Tl l
01
through the 115-volt line
fuse
Fll
01,
POWER switch
SWl
101,
thermal cutout TKl 101, Voltage Selector switch
SWl
102
and
Range Selector switch
SWl
103.
The
Voltage Selector switch
SWl
102 connects the split primaries
of
Tl
101
in parallel for
115-volt nominal operation,
or
in series
for
230-volt nominal
operation. A second line fuse, Fl 102,
is
connected into the
circuit when the Voltage Selector switch
is
set
to the 230 V
position to provide the correct protection
for
230-volt opera-
tion
(Fl
102
current rating
is
one-half
of
Fl
101
).
The
fan
is
connected across one
half
of
the split primary winding
so
it
always
has
about
115
volts
applied
to
it
(SN
20,000 to
SN
30,720 only).
The
Range Selector switch,
SWl
103, allows the instrument
to regulate correctly on higher
or
lower
than normal line
voltages.
Each
half
of
the primary
has
taps above and
below
the 115-volt
(230)
nominal point.
As
the Range Selec-
tor switch,
SWl
103,
is
switched from LO to M to HI, more
turns are effectively added to the primary winding and the
turns ratio
is
decreased.
This
provides a fairly constant volt-
age in the secondary
of
Tl
101
even through the primary
voltage
has
increased.
Thermal cutout TKl
101
provides thermal protection
for
this
instrument. If the internal temperature
of
the instrument ex-
ceeds a safe operating level, TKl l
01
opens to interrupt the
applied
power. When the temperature returns to a safe
level, TKl
101
automatically closes to reapply the power.
- 12-Volt Supply
The
-12-Volt
Supply provides the reference voltage for
the remaining supplies.
The
output from the secondary
of
Tl l
01
is
rectified by bridge rectifier
Dl
l 12A-D.
This
voltage
is
filtered by
Cl
112
and then
applied
to the
-12-Volt
Series
Regulator stage to provide a stable output voltage.
The
Series Regulator can
be
compared to a variable resistance
which
is
changed to control the output current.
The
current
through the Series Regulator stage
is
controlled
by
the Error
Amplifier
to provide the correct regulated output voltage.
"Cutler,
pp.
559-625.
3-25
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