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-Model
181A/AR
4-76. NORMAL.
Selection of this mode
permits the
Model 181A/AR tobe employedas a conventional oscil-
loscope.
With NORMAL
activated,
the junction of
A6R16/A6R19 is grounded and the storage mesh falls
to -25v.
Because of this negative potential, the vari-
able persistence and storage capabilities are therefore
disabled.
4-77. WRITE and MAX WRITE.
Operating in these
modes allows normal viewing of the display and pre-
pares
it for storing.
MAX WRITE
is used only when
necessary,
suchas in viewing fast single-shot signals.
' 4-78, To obtain display uniformity in the MAX WRITE
mode,
the CRT collimator voltage should be readjusted
in this mode.
Todo so, a multivibrator
consisting of
A6Q16 and A6Q17 is used.
4-19. Whenthe MAX W. pushbutton is depressed,
one
side of the multivibrator
conducts.
Current flow
through A6R47 and A6R46 holds A6Q16 on and A6Q17
off.
Thus, the MAX WRITE ADJ pot A6R17 is para-
lleled with WRITE ADJ.
Atthe same time,
A6R9 is
disabledand MAX WRITE
COLLIMA TION ADJ (A6R29)
is enabled.
The multivibrator
is necessary so that
proper collimation voltage is retained when the VIEW
or STORE mode is selected.
4-80. The setting of the WRITE adjust, A6R18, adjusts
the positive pulse level at the collector of A6Q4 when
operating in the WRITE mode, while A6R18 in parallel
with the MAX WRITE adjust, A6R17,
adjusts the level
in the MAX WRITE mode.
Pulse level control of the
1 kHz pulsestothe storage mesh affords depth of eras-
. ure control
which directly affects
writing
rate.
In
other
words,
the more
negative the storage surface
becomes,
the longer it will take ittobuilduptoa level
high enough to store a trace (refer to Figure 4-4).
4-81. STORE.
When the STORE function is selected,
the base of A6Q1 is grounded, turning it off.
This
allows the current flow through A6R2 and A6CRI to
turn A6Q2 on.
Meanwhile, the «15v square wave sig-
nalatthecollector of A6Q3 is differentiated by A6C1/
A6R2 and applied to the base of A6Q2 through A6CR1.
Thus A6Q2 hasa negative voltage developed at its base
during the charging time of A6C1 which turns it off.
The time constant of AGCI/A6R2 is such that A6Q2 is
off for about 50 microseconds
each millisecond,
and
only during this short interval will a positive poten-
tial be applied to the flood gun accelerator grid.
4-82. While A6Q2
is on,
the flood
gun
accelerator
voltage
is established by voltage divider network,
A6R5/A6R6, at -9v.
With A6Q2 switched off by the
differentiated 1 kHz pulse,
the accelerator
voltage is
443v set by the divider network A6R4, and A6R6.
4-83. With the accelerator grid held at -9v, the flood
gunelectronsarerepelled.
Thus,
when in the STORE
mode, the flood guns are always on, but electronsare
attracted
to the storage mesh only when the acceler-
. ator
grid is at a positive
potential,
about 5% of the
time.
This reduces
the display brightness and pro-
vides for greatly increased storage time.
4-84. VIEW.
Depressing the VIEW push button allows
viewing à previously stored display at a brightness
level determined by the intensity and persistence set-
|
tings duringthe writing process.
At least one minute
02612-2
Section IV
Paragraphs 4-76 to 4-89
of aggregate viewing is available without trace degrad-
ation.
4-85. When
in VIEW,
NORMAL,
WRITE
or MAX
WRITE mode
of operation, A6Q1
is turned on by the
currentflowthroughA6Rltoitsbase.
This effectively
grounds the base of A6Q2, holding it off and keeping
the flood gun accelerator potential at 43v.
4-86. The flood gun grid levelis setto provide an op-
^
timum flood gun electron distribution at.the storage
mesh.
This is adjustable and is determined by the .
setting of A6R42, whichis in series with ASR? and the
-100v supply.
Stray ac signals on the flood gun grid
lead are decoupled from the flood gun by A6C4.
4-87. ERASE.
The push button operating mode selec-
tor switch does not permit
energizing the erase cir-
cuitry unless
the WRITE
or MAX
WRITE
mode
of
operating has been selected.
Activationof the ERASE
switch S7 (refer to Figure 8-12) in either of these modes
`
applies +156v tothe CRT storage meshandto the junc-
tion of A6R36 and A6CR6.
The diode A6CR6 prevents
application of this +156vtothe collector of A6Q4 during
ERASE, while A6CR4 prevents the collector from ris-
ing above
+15v because
of the +100v applied through
'the voltage divider formed by A6R15, A6CR5, A6R16
and A6R19.
Normally nonc onducting, A6Q13 is turned
on by application of the «156v which in turn shuts off
A6Q12.
Thispermits A6C6to charge positive through
A6R33 and A6R37 to about 44. 7v.
Theresultant cur-
.rentthrough A6R37 causes A6Q14 toconduct and A6Q15
to cease conduction.
Currentflowingthrough A6R43,
A1CR15,
AIR10 and into the emitter of A1Q1 causes
the Gate Amplifier to operate so as to blank the CRT
write gun.
A clean erasure
of the storage mesh is
thereby assured since no writing of an input signal can
take place during erasure.
4-88. Releasingthe ERASE switch removes the «156v
fromthe CRT storage meshand from A6R36.
Current
no longer flowsthroughthe base of A6Q13 and conduc-
tionceases.
This permits A6Q12to conduct due to the
current flow through A6R34 into its base.
The result-
ing 4. 7v negative step atthe collector of A6Q12 is dif-
ferentiated by A6C6/A6R32 and applied to the base of
A6Q11,
causing
it to cease conduction.
As a result
of the charging time constant of A6R32 and A6C6, A6Q11
will remain ina nonconducting state for approximately
100 milliseconds.
During this time, A6C5 is being
charged to «4.5
v through A6R31, AO6R38, and A6R2T.
Current flow through A6R38 and A6CRT7
causes the
Blanking Control Amplifier A6Q14/A6Q15 and the Gate
Amplifier to operate and blank the CRT write gun.
4-89. Control of the voltage applied to the CRT colii-
mator is desired during storage mesh erasure.
A por-
tion of the current through A6R31 also flows through
A6R27,
placing A6Q8 in a conducting state, and caus-
ing A6Q9 tocease conduction.
The voltage on the base
of A6Q10,
therefore,
rises to nearly «120v,
causing
heavy conduction through A6Q10.
"This results in its
emitter rising to about «120v due to the voltage drop
across A6R30.
Since the collimator is connected to
the emitter
of A6Q10,
the + 120v developed
across
A6R30 is appliedto the collimator while erasing.
This
ensures
a more uniform erasure of the storage mesh,
particularly of the periphery of the display area.
4-9
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