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Model 181A/AR
UNBLANKING
GATE
' CHOPPED
BLANKING
Z-AXIS
INPUT
PULSE
INPUT
-100V —
x
INT
;
DISPLAY —
(-100V)
|...
VERT
BEAM
FINDER
FIND BEAM]
^
-26V —
/
INTENSITY
9l
Section IV.
Paragraphs 4-60 to 4-67
"AMPLIFIER
UNBLANKING
SIGNALS
DIFFERENTIATOR
ALTERNATE
TRIGGER
iBIA- B--3A
Figure 4-8.
Gate Amplifier Block Diagram.
R6, maintainsthe write gun filamentat cathode poten-
tial.
The voltage tripler circuit of ASCR1-3and A9C1-4
is contained
on Assembly A9, the output of which (+7
kv) is applied to the CRT post-accelerator
anode.
4-60. Changes in output of the -1440vdc supply are de-
tected by the regulator A1Q8-A1Q10tochange the oper-
ating voltage of oscillator Q5.
Assume that the - 1440
supply voltage decreases (goes positive).
Apositive-
-
going signal
is applied through the regulator
to the
base of Q5, causing it to conduct for a greater portion
oftheinputcycle.
The oscillation amplitude is there-
fore varied so as to oppose the original change in out-
put voltage.
This causes a voltage change to appear
on the primary of A5T1 and increases the voltage
of
the secondary.
The steady state value of the CRT
cathode
voltage is established by A1R38,
the High
Voltage Adjust,
by setting the normal dc value on the
base of the A1Q8.
Inductor A4L1 suppresses any pos-
sible high frequency parasitic oscillation.
4-61.
GATE
AMPLIFIER.
4-62. The inputs to the gate amplifier (refer to Fig-
ure 4-8) aretheunbianking gate, the chopped blanking,
the Z-AXIS INPUT,
andthe storage pulse circuit sig-
nals.
These four signals may be present either singly
or simultaneously,
depending upon control
settings.
They are summed with a current established by three
-front panel controls--FIND BEAM,
INTENSITY,
and
HORIZONTAL DISPLAY.
Depressing
FIND
BEAM
. shunts the normally adjustable INTENSITY
control.
and supplies maximum
currentfrom this source.
Set-
ting HORIZONTAL
DISPLAY
to EXT SENS
or EXT
CAL supplies additional current to brighten the beam.
4-63. The gate amplifier,
A1Q1-A1Q4,
senses the in-
put signal current,
convertsitto a voltage,
amplifies
it, and couples itto the control grid of the CRT write
gun.
And in addition, the output signal is also differ-
entiated,
clipped,
and coupled to the Vertical Plug-
In for use as a trigger signal if desired.
02612-2
4-64. The
input currents to the gate amplifier (refer
to Figure 8-7)
are summed
in the low impedance
emitter circuit of A1lQ1.
The resulting current is.
coupled to the complementary feedback amplifier (a
current fed operational amplifier), A1Q2-A1Q4, where
it is converted to a voltage and coupled to the control
grid of the CRT write gun.
The large negative feed-
backfromthe collectors of A1Q3 and A1Q4 to the base
of A1Q2 provides the complementary feedback ampli-
fier with a very stable gain,
Trimmer
capacitors,
A1C8 and A1C9,
adjust the high frequency feedback.
Diode A1CR6 provides temperature compensation for
A1Q3, while AICR7 and A1CR8 protect A1Q3 and A1Q4
from voltage breakdown.
Diode, A1CR10 and A1R5T,
isolate A1Q3 and A1Q4 from the high voltage inthe con-
trol grid circuit of the CRT write gun in the event of
a grid or cathode short to ground.
The output from
A1Q3andA1Q4 is differentiated by A1C13,
A1R22 and
A1R23, andcoupled through A1Q5 andthe positive clip-
per, AÍCRi1i,
to the Vertical Plug-In for alternate
triggering purposes.
4-65.
HORIZONTAL
AMPLIFIER.
4-66. The block diagram,
Figure 4-9, illustrates the
majorcircuitfunctions.
The horizontal amplifier can
be driven by either an internally derived signal or by
an external signal applied to the HORIZONTAL
EXT
INPUT
front panel BNC
jack.
Positioning the HORI-
ZONTAL DISPLAY controlto INT disconnects the ex-
ternal signal input and grounds the horizontal preamp-
lifier input.
The Internal Sweep signal is connected
through the HORIZONTAL DISPLAY switch to the hor-
izontal output amplifier.
4-67. The EXT
INPUT
BNC, J4, is connected to the .
input of the preamplifier when either EXT SENS or
EXT CAL
is selected;
the preamplifier,
in turn, is
coupledtothe outputamplifier.
Selections of EXT SENS
permits varying theamplitude of the preamplifier out-
put by adjustment of the HORIZONTAL DISPLAY con-
4-7
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