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Section IV
Paragraphs 4-68 to 4-75
DISPLAY
Model 1814/AR
O
|
t
CRT
HORIZONTAL
DEFLECTION
PLATES
R3
o HORIZONTAL
E
POSITION
I8LA—B—2
Figure 4-9.
Horizontal Amplifier Block Diagram.
trol.
When
EXT
CAL is selected,
this control,
Ri,
is shorted; the output amplitude,
therefore,
is deter-
mined by the amplitude of the input signal.
4-68. The signal selectedis fed into the output ampli-
fier where it is summed with a current established by
the HORIZONTAL
POSITION controls.
Theresultant
current
is converted to a differential signal, ampli-
fied, andappliedto the C RT horizontal deflection plates.
4-69, External input signalsare preamplified by A3Q1
. and A3Q2 (refer to Figure 8-10).
The high input im-
pedance of A3Q1 minimizes loading of the external in-
put source.
Diode A3CR1
protects A3Q1 from high
level inputs.
A3Q2
has a low output impedance suit-
able for driving A3Q3.
The BANDWIDTH/PHASE
Switch, A3S1, would be positioned in PHASE when accu-
rate X-Y
measurement
is desired.
In the PHASE
position, A3C2and A3C3 arè switched in, decreasing
the preamplifier bandwidth.
'Thetotalhorizontalamp-
lifier
signal delay
is therefore made equal to signal
delay
in the Vertical Plug-In.
The vernier
balance,
ASR",
is adjusted so that 0 vde appears across the
HORIZONTAL
DISPLAY control, thus eliminating any
horizontal dc shift as the control is operated.
4-70. Input signals to A3Q3 are summed in the low im-
pedance emitter circuit with a current established by
the setting of the POSITION controls A3R2 and A3R3.
A3Q6
is driven by the low impedance
of emitter fol-
lower
À3Q4.
The
input signal to A3Q6
is coupled
through the MAGNIFIER
switch, $4, tothe complemen-
`
tary driver
A3Q7.
S4 provides for selection of incre-
mental gain levels by selecting the amount of emitter
degenerationemployed with A3Q6 and A3Q7.
Increas-
ing degeneration decreases gain. Adjustment A3R30
along with A3R31
controls
the gain when in the X10
position, A3R32/A3R33 control the X5 gain, and A3R34/
AS3R35determinethe X1 horizontal gain,
The dc bal-
ance of A3Q6
and A3Q7
is adjusted by A3R37
which
controls the emitter potentials.
Transistor A3Q5 pro-
vides a low impedance
voltage source for the base of
ASQ.
The differential signalat the collectors of A3Q6
and A3Q7
is applied to the complementary feedback
amplifiers
(current-fed amplifiers),
A3Q8-Q10
and
A8Q11-Q13,
convertedtoa voltage, and coupled to the
horizontal deflection plates of the CRT.
A3CR3 pre-
vents A3Q6 from saturating,
while A3CR6
serves the
same
purpose
for A8Q7.
Diodes A3CR2/CR4
and
4-8
. wave signal.
A3CR7/CR8 limit the amplifier output to the CRT de- .
flection plates to within+6vand «94v regardless of the
amplitude of the input signal.
4-11. Depressing FIND BEAM switch 83 disables lim-
iter ASCR7 /CR8 andblocks the input signal to A3Q11.
The differentialgainis effectively reduced by half and
the electron beam is confined to the horizontal limits
of the CRT
screen.
4-12. The gain of the complementary feedback ampli-
fier is made very stable by coupling a generous amount
of negative feedback from the collectors of A3Q9/Q10
to the base of A3Q8, andfrom the collectors of A3Q12/
Q13 to the base of A3Q11.
The high frequency feed-
back of each amplifier is adjusted by A3C6 or A3C19
individually, while A3C9 adjusts the feedback for both.
Diodes A3CR5 and A3CR9 provide temperature compen-
sation for A3Q10 and A3Q13.
4-73.
PULSE
CIRCUIT.
4-14. Pulses of adjustable level and width are used to
controlthe variable persistence and storage capability
of the Model 181A/AR Oscilloscope.
They are ap-
plied to the
CRT storage
mesh when
operating in the
WRITE
and MAX WRITE
modes,
applied to the flood
gun accelerator in the STORE mode, and used to key
the gate amplifier for CRT unblanking.
4-75, VARIABLE
PERSISTENCE,
The multivibrator
circuit, (Figure 8-17), isthe source of a 1 kHz square
This signal,
in turn, is applied to the
pulse circuit which modifies the width and level of the
pulse.
A -100v square wave is obtainedfrom the junc-
tion of A1C14 and A1R28 and fed to the base of A6Q3
through A6R8.
Inverted and level-shifted by A6Q3,
the resultant «15v square wave atthe collector of A6Q3
is applied through A6CR2 and differentiated byA6R13/
A6C2.
Applied to the base of A6Q4 through A6CR3,
the amplitude of the pulse at the anode of AGCR3
is
established by the ratio of AGR12 andthe PERSISTENCE
control setting,
R9.
Asaresult of the charging time
constant of A6C2/A6R13,
the variable amplitude sig-
nalisfeltas a variation in width (i.e. duration) at the
base of A6Q4.
By varyingtheconduction time of A6Q4,
thetime requiredtoeraseatrace
has been controlled.
In other words, varying the erase time is essentially
the same as varying
the display time,
and this, in
turn, is known as variable persistence.
02612-2
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