Circuit
Description-Type
453/R453
Input Amplifier stage to a push-pull output signal which
is
necessary to drive the horizontal deflection plates of the
CRT.
In
all positions of the
HORIZ
DISPLAY
switch except
EXT
HORIZ,
a positive-going sawtooth signal
is
connected
to the base of Q834 through Q814.
This
produces a nega-
tive-going sawtooth voltage
at
the collector of Q834.
At
the same time, the emitter of Q834 goes positive and
this
change
is
connected to the emitter of Q844 through the
gain-setting network,
R835-R836-R845-R846.
In
all positions
of the
HORIZ
DISPLAY
switch except
EXT
HORIZ,
no
signal
is
connected
to
the base of Q844 through Q824
so
that Q844
operates as the emitter-driven section of a paraphase amp-
lifier. Then, the positive-going change
at
its
emitter
is
amp-
lified to produce a positive-going sawtooth signal
at
the
collector.
Thus
the single-ended input sawtooth signal has
been amplified and
is
available as a push-pull signal
at
the
collectors of Q834 and Q844.
In
the
EXT
HORIZ
position of the
HORIZ
DISPLAY
switch,
the external horizontal deflection signal
is
connected to the
base of Q844 through Q824 and the sawtooth signal
at
the base of Q814
is
disconnected. Now, the circuit operates
much
the same as
just
described
with
the sawtooth input.
A positive·-going external horizontal deflection signal pro-
duces a negative-going change
at
he
base of Q844 which
decreases the current
flow
through
this
transistor.
The
col-
lector of Q844 goes positive while the emitter-coupled signal
to Q834 produces a negative-going change
at
the collector
of Q834.
This
stage also provides adjustment to set the normal and
magnified gain of he Horizontal Amplifier circuit, and the
MAG
switch to provide a horizontal sweep which
is
mag-
nified
10
times.
For
normal sweep operation
(MAG
switch
set to
OFF),
R835
and
R836
control the emitter degeneration
between Q834 and Q844 to set the gain of the stage.
R835,
Normal Gain,
is
adjusted to provide calibrated sweep rates.
When the
MAG
switch,
SW801
B,
is
set
to
the X
10
position,
R845
and
R846
are connected
in
parallel
with
R835
and
R836.
This
additional resistance decreases the emitter degen-
eration of
this
stage and increases the gain of the circuit
10
times.
R845,
Mag Gain,
is
adjusted to provide calibrated
magnified sweep rates. When the
MAG
switch
is
set to
X
10,
the
MAG
ON
light,
8849,
is
connected
to
the +
150-
volt supply through
R849.
8849
ignites
to
indicate that the
sweep
is
magnified.
In
the
EXT
HORIZ
position of the
HORIZ
DISPLAY
switch, the magnifier
is
connected into the circuit
so
the horizontal gain
is
correct
for
external horizontal
operation regardless of the setting of the
MAG
switch.
However, both sides of
Bl
049
are connected
to
ground
so
it
does not ignite.
Output Amplifier
The
push-pull output of the Paraphase Amplifier
is
con-
nected to the Output Amplifier.
Each
half of the Output
Amplifier can be considered as a single-ended, feedback
amplifier which amplifies the signal current
at
the input
to
produce a voltage output
to
drive the horizontal deflection
plates of the
CRT.
The
amplifiers have a
low
input imped-
ance and require very little voltage change
at
the input
to
produce the desired output change. Diodes
D851-D852
and
D861-D871
protect the amplifier
from
being overdriven
by
excessive current swing
at
the collectors of Q834 and Q844.
Negative feedback
is
provided
from
the collectors of the
final transistors,
0884
and Q894,
to
the bases of the input
3-22
transistors through
C882-R882
and
C892-R892.
C882
and
C892
adjust the transient response of the amplifier
so
it
has
good linearity
at
fast sweep rates.
The
Mag Register adjustment,
R855,
balances the quiescent
DC
current
to
the base of Q863 and
0873
so
a center-screen
display does not change position when the
MAG
switch
is
changed
from
X
10
to
OFF.
The
TRACE
FINDER
switch, SW330, reduces horizontal
scan
by
limiting the current available
to
Q884 and Q894.
Normally the collectors of these transistors are returned to
+
150
volts. However, when the
TRACE
FINDER
switch
is
pressed
in,
the power
from
the unregulated + 150-volt supply
is
interrupted and the collector voltage
for
Q884 and Q894
is
supplied
from
+75
volts through
D884.
Since the collectors
are
returned to a lower potential, the output voltage swing
is
reduced to
limit
the horizontal deflection within the grati-
cule area.
Z AXIS
AMPLIFIER
General
The
Z
Axis
Amplifier circuit controls the
CRT
intensity
level
from
several inputs.
The
effect of these input signals
is
to
either increase or decrease the trace intensity, or
to
completely blank portions of the display.
Fig.
3-15 shows a
detailed block diagram of the Z
Axis
Amplifier circuit. A
schematic of
this
circuit
is
shown
on
diagram
16
at
the
rear of
this
manual.
Input Amplifier
The
input transistor, Q1014,
in
the Input Amplifier stage
is
a current-driven, low-input impedance amplifier.
It
provides termination for the input signals as well as isola-
tion between the input signals and the following stages.
The
current signals
from
the various control sources are
connected to the emitter of
Ql
014
and the
sum
or differ-
ence of the signals determines the collecter conduction
level.
Dl
015
and
Dl
016
in
the collector provide limiting
protection
at
minimum
intensity. When the
INTENSITY
con-
trol
is
set
fully
counterclockwise
(minimum),
the collector
current of
01014
is
reduced and
its
collector
rises
positive.
Dl
015
is
reverse biased to block the control current
at
the
base of Ql023, and
Dl
016
is
forward biased to protect
the circuit
by
clamping the collector of
01014
about
0.5
volts more positive than the emitter level of 01023.
This
limiting action also takes place when a blanking signal
is
applied. The clamping of
Dl
016
allows
Ql
014
to recover
faster to produce a sharper display with sudden changes
in
blanking level.
At
normal intensity levels,
Dl
016
is
reverse
biased and the signal
from
Ql
014
is
coupled to emitter
follower
01023
through
Dl
015.
The
input signals vary the current drive to the emitter of
Ql
014,
which
produces a collector
level
that determines the
brilliance of the display.
The
INTENSITY
control sets the
quiescent
level
at
the emitter of
Ql
014.
When
Rl
005
is
turned
in
the clockwise Jirection, more current
from
the
INTENSITY
control
is
added
to the emitter circuit of 01014
which results
in
an increase
in
collector current to provide a
brighter trace. However, the vertical chopped blanking, Z
Axis
Input and A and B unblanking signals determine whether
the trace
is
visible.
The
vertical chopped blanking signal
blanks the trace during foal-trace switching.
This
signal
®I
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