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Circuit
Description
—Type
502A
(or
C440 for Input B) plus the tube and stray capacitance.
C410 is then adjusted so
that the total input capacitance
is
47 pf.
When
the
X100 attenuator is connected
into the circuit,
C406L
(or C407L
for Input B) shunts the 47 pf capacitance.
This value
of capacitance is then reduced to
a very small
value by
series
capacitor C406J (or C407J). The capacitor
at
the input to the attenuator
then
shunts this small capa
citance, and
is
adjusted to make the total capacitance 47 pf.
The
X10 attenuator is designed in the same manner, except
that
stray capacity forms the lower
branch of the divider.
Since
the
attenuator networks are frequency-compensated
voltage
dividers, a constant attenuation ratio is maintained
from
DC to the upper-frequency limits of the Vertical Ampli
fiers.
The Input
Amplifier
When
the
Input Selector
switch is in the A position (either
AC- or DC-coupled) the
grid of V414 is connected to the
input
circuit
and the grid of V444 is returned to ground
either
through the
switch or through one of
the
series at
tenuator
networks. When in position B (AC
or DC), V444
is
the input tube
and V414 is the grounded-grid tube. With
either of
these configurations, the
Input Amplifier is a
cathode
coupled, paraphase
amplifier; it converts a single-
ended
input
signal to a push-pull output signal.
The
cathode
resistor
R408 plays an important role in
determining
the amount
of negative feedback applied to
the
Input Amplifier stage.
As
mentioned previously, this
feedback
voltage comes from the cathodes of the Driver
C.F.
stage
and the
Output Amplifier stage. The feedback
from
the Driver
C.F.
stage is applied through a divider
consisting of
R470 on one side and R408, and R480 on the
other
side of R408. To
this compensated feedback network
is
added a
small
amount
of feedback
from the uncompen
sated
network of R465
and R467. This feedback from the
Output
Amplifier stage helps in positioning the trace.
The smaller
the value
of R408 the greater the drop across
the
series
resistor (R470, R480, R465, and R467) and the less
the
negative feedback applied to the Input Amplifier stage.
Conversely, the greater
the value of R408 the
greater
the
drop
across
it
and the greater the negative feedback. Thus,
for
very small
input voltages, when the SENSITIVITY switch
is
set so that
the resistance of R408 is quite small,
there is
very
little negative feedback and the Input
Amplifier stage
operates with
high gain. When the
SENSITIVITY switch
is
set
to accommodate larger input voltages the resistance
of R408
is increased. This means that there is a greater
amount
of negative feedback and the gain
of the Input
Amplifier stage is
decreased.
The switch
diagram shows
the makeup of R408. R408A is
in
the
circuit
for all positions of
the SENSITIVITY switch
In
the .2, 2, and 20 VOLTS/CM positions of the switch, R408A
alone
makes up
the resistance of R408. In all other positions
of
the switch R408A is shunted by at least one other resistor.
In
the .1
mVOLTS/CM
position R408A
is shunted by both
R408L
and C409L; in the .5 mVOLTS/CM through
.1 mVOLTS/
CM positions,
and
in the .5, 1, 5 and
10 VOLTS/CM positions,
it
is
shunted
by
both a resistor and an R-C network. The total
value
of R408
is determined by the degree to which R408A
is
shunted. The greater the shunting of R408A the smaller
the
value of R408
and the greater the gain of the Input
Amplifier
stage. Conversely,
the less the shunting
of R408A
the
greater the values of
R408 and the smaller the gain of
the
stage.
The
cathodes of the
Input Amplifier stage are "long-tailed"
to the —
150
volt supply through 82.5K resistors
and R429
(VAR
DC
BAL).
With
the grids of
the Input Amplifier at ground potential,
the
cathodes will operate very close to ground (actually,
a
couple
of
volts positive to bias the stage). The approx
imately
150
volt drop across the 82.5K cathode resistors
(R427
and R428) and R429 provides a
constant supply of
cathode
current to
stabilize the performance of the 6AU6
Input
Amplifier
tubes.
In
order
for the Input Amplifier stage to remain in a
state of
DC balance, there must be no dc voltage drop
across R408
when there is
no input signal. This means that
the
difference in potential between
the two cathodes must
always
be
zero, regardless of the value of R408. In order
to provide for
equal cathode voltages under this condi
tion,
the screen voltage of the two tubes can be varied
with
respect
to each other with the DC BAL Control. Any
change
in the
voltage at the screens will be reflected to the
cathode
by
a factor
of 1/μ. (the screen grid μ) and thus the
cathode
voltages can be equalized.
Along with the
DC BAL Control, the
DC unbalance in
the
Input Amplifier tubes is
also removed by R429. Adjust
ment
of this
control
will remove any vdltage change which
might
be
seen as a positioning change by the Output
Amplifier.
Vertical
positioning
of the crt beam is accomplished
through
the
action
of the POSITION control. This is a dual
control,
connected
between —150
volts and +100 volts.
It is
wired
so that as the voltage between —150 volts and
the
movable arm
in one
side increases, the voltage between
—150
volts and
the movable
arm in the other decreases.
A change
in the
setting of the POSITION Control will
produce a
large change in the cathode voltage
of
the
Output
Amplifier stage
and at the same time produce a
small
voltage change at the cathodes of
the Input Amplifier
stage. However,
the compensated negative feedback
circuit
of
the
Driver
C.F. stage reacts quickly to prevent any
change
in the cathode voltage of the Input Amplifier
stage,
and as
a result a change in the voltage at the
cathodes
of the Driver C.F. stage
is produced. This change
in voltage at the
cathodes
of
the Driver C.F. stage along
with
the voltage
change at
the Output Amplifier cathode,
is
amplified by
the Output Amplifier
and appears as a
change
in the positioning voltage at
the vertical-deflection
plates.
When
the Input Selector switch is set to the A-B
DIFF
position
both grids
of the Input Amplifier stage are connect
ed
to the Input circuit. With
this configuration the
Input
Amplifier
stage is connected for differential operation.
Two
input voltages are required,
and the push-pull output
voltage is proportional
to the difference between the two
input
voltages.
The
.2 MV/CM DIFF BAL Control R435 adjusts the plates
of
the Input Amplifier stage for equal voltages
when
common mode
signals
are applied to the grids. This control
is
equally
effective in
all
positions of the SENSITIVITY
switch,
but is primarily
adjusted in the high-sensitivity
position
(.2 mVOLTS/CM). The .2V/CM DIFF BAL control
3-3
Содержание 502A
Страница 4: ......
Страница 22: ...Circuit Description Type 502A Fig 3 2 Simplified Sweep Trigger Circuit t i CO ...
Страница 27: ...Circuit Description Type 502A Fig 3 4 Simplified Horizontal Amplifier 3 9 ...
Страница 30: ...Circuit Description Type 502A 3 12 NORMALLY CLOSED LOCATED ON REAR PANEL Fig 3 6 Simplified CRT Circuit ...
Страница 32: ...Circuit Description Type 5O2A Fig 3 7 Simplified Calibrator Circuit 3 14 ...
Страница 34: ...NOTES ...
Страница 56: ...NOTES ...
Страница 60: ...Parts List Type 502A LEFT SIDE 6 4 ...
Страница 64: ...Parts List Type 502A RIGHT SIDE 6 8 ...
Страница 67: ...Parts List Type 502A TOP 6 11 ...
Страница 70: ...Parts List Type 502A BOTTOM 6 14 ...
Страница 73: ...Parts List Type 502A REAR 6 17 ...
Страница 89: ...TYPE 502A OSCILLOSCOPE A ...
Страница 90: ...A BLOCK DIAGRAM MRH Z6 3 ...
Страница 91: ... TYPE 502A OSCILLOSCOPE A ...
Страница 92: ...A CIRCUIT NUMBERS 1 THRU 59 I Ixj 263 TIME BASE TR IGGER ...
Страница 93: ......
Страница 95: ...TI M I NG RESI 5TORS TIMING CAPACITORS TYPE 502A OSCILLOSCOPE ...
Страница 96: ...SWI6O HOLD OFF CAPACITORS 4 RESISTORS TIM ING CAPACITORS o A TIMING SWITCH job ...
Страница 98: ... 1 INPUT AMPLIFIER OUTPUT AMPLIFIER A CIR CUIT NUMSER 5 300 THR U 399 ZG3 joe ...
Страница 100: ...CMO 363 VERTICAL ATTENUATOR SWITCH A ...
Страница 103: ...TYPE 5O2A OSCILLOSCOPE OOM HEATER WIRING DIAGRAM ...
Страница 104: ...POWER SUPPLY CIRCUIT NUMBERSI 600 THRU 799 ...
Страница 106: ...CIR CUIT NUMBER S 800 THR U 869 CRT CIRCUIT c 9G4 ...
Страница 107: ...CA LIBp A TOp MULTIVIBP A TOR 1 IOOV o TYPE 5O2A OSCILLOSCOPE A ...
Страница 108: ...CAL OUT CF CALIBRATOR A CIRCUIT NUMBERS 8 7O THRU 899 4Z ...
Страница 110: ...TYPE 502A TENT S N 23430 PARTS LIST CORRECTION CHANGE TO V152 157 0104 01 Selected 6AL5 M913U 665 ...