Tektronix 531 User manual

CATHODE RAY OSCILLOSCOPE
TYPE 531/541
INSTRUCTION
MANUAL
TEKTRONIX, INC.
MANUFACTURERS OF CATHODE-RAY AND VIDEO TEST INSTRUMENTS
Sunset Highway and Barnes Road ¢ P.O.Box 831 © Portland 7, Oregon, U. S.A.
Phone: CYpress 2-2611 ¢ Cables: Tektronix
070-203

NOTE
This instruction manual has been prepared to
cover TEKTRONIX Type 531/541 Oscilloscopes of
all serial number ranges. Text, diagrams, and
parts lists have been expanded to incorporate all
circuit modifications adopted during the course of
manufacture. The serial ranges of instruments to
which various modifications were applied before
shipping from the factory have been noted wher-
ever necessary.
However, because many instruments have been
modified in the field and out of serial sequence,
component values and circuitry of a given instru-
ment may differ considerably from those indicated
in this manual for its serial number. Theuser is
urged, therefore, to enter whatever changes may
be necessary to bring this manual intoagreement
with the present circuitry of his oscilloscope.
When ordering parts, always include the fol-
lowing information:
Instrument Type (531/541).
Instrument Serial Number (as, S/N 9999).
Part Circuit Number (as, R999).
Part Description (value, type, rating,
tolerance, etc.).
5. The 6-digit TEKTRONIX part number (as,
999-999),
kone
SAFETY NOTICE
This oscilloscope employs dangerously high voltages, Since
some maintenance must of necessity be performed with the
case removed, great care should be taken. Use only insulated
tools, stand on a dry floor and if possible keep one hand in
your pocket. Care should also be used in making any con-
nections to the deflection plates of the cathode-ray tube through
the access panel. It is advised that the access panel never be
removed until the power has first been turned off. The instru-
ment should not be operated with this protective cover removed,

CONTENTS
GENERAL DESCRIPTION SECTION 1
Characteristics. Functions of Front-Panel Controls and Connectors.
OPERATING INSTRUCTIONS SECTION 2
Preliminary Instructions. First-Time Operation. Triggering Modes.
‘Triggering Instructions. Sweep Operation. Auxiliary Functions. Sim-
plified Sweep Diagrams.
CIRCUIT
DESCRIPTION
SECTION
3
Block Diagram. Vertical-Deflection System. Horizontal-Deflection
System. Power Supply. CRT Circuit.
MAINTENANCE SECTION 4
General Information. Trouble Shooting. Recalibration Procedure.
PARTS
LIST
SECTION
5

SECTION 1
GENERAL DESCRIPTION
NOTE
The
Types
531
and
541
are
high-speed
laboratory
oscilloscopes,
designed
for
general
laboratory
use.
Their
extremely
fast
rise-
time,
wide
sweep-speed
range
and
10-kilovolt
accelerating
volt-
age
permit
accurate
analysis
of
many
types
of
waveforms.
Addi-
tional
adaptability
is
provided
by
plug-in
preamplifiers
which
extend
the
use
of
these
oscilloscopes
to
practically
all
laboratory-
oscilloscope
applications.
Accurately
calibrated
sweep
speeds
and
vertical-deflection
sensitivity
permit
quantitative
time
and
amplitude
measurements
to
be
made.
CHARACTERISTICS
Cathode-Ray Tube
A Tektronix 5-inch post-deflection accelera-
tion cathode-ray tube is furnished with the in-
strument.
With
10-kv
acceleration
potential
the
trace is bright enough that a single sweep can be
photographed
with
a
Pll
screen
even
at
the
fast-
est sweep speeds. A P2 phosphor is furnished
unless other phosphors are specially requested.
Vertical-Deflection System
A dc-coupled vertical amplifier in the main
unit
is
adjusted
for
optimum
transient
response
and
wide
passband.
A
plug-inchannel-switching
unit
provides
a
dual-trace
presentation
for
re-
petitive
signals.
Input
to
the
vertical-deflection
system
must
be
made
through
one
of
the
avail-
able types of plug-in units.
Horizontal-Deflection System
Sweep Circuit
The linear sweep generator is a Miller runup
generator
with
excellent
linearity,
and
the
ex-
tremely
wide
speed range
of
.02
microseconds
per centimeter to 12 seconds per centimeter.
Twenty-four
calibrated
sweep
speeds
are
avail-
able
accurate
within
three
per
cent.
The
main
sweep
control
has
eight
positions,
.1,
1,
10,
and
100
microseconds
per
centimeter,
1,
10,
100
milliseconds
per
centimeter,
and
1
second
per
centimeter.
Three
multiplier-switch
positions
1, 2,
and
5
times,
provide
a
total
of
twenty-
four
speeds.
Remaining
positions
of
the
multi-
plier
switch
provide
continuously
adjustable
ie
531/54I—GENERAL. DESCRIPTION
multipliers of 1 to 2.5 times, 2 to 5 times, and
5 to 12 times so that the above range is also
covered
continuously.
The
five-times
sweep
magnifier increases the maximum sweep speed
to .02 microseconds per centimeter.
Magnifier
Sweep magnification is produced by increasing
the sweep output amplifier gain five times. The
center two centimeters of the trace is expanded
to 10 centimeters, Any one-fifth of the sweep
so magnified can be positioned to show on the
screen by means of the HORIZONTAL POSI-
TION control.
DC-Coupled Unblanking
The
unblanking
square
wave
is
dc-coupled
to
the
grid
of
the
cathode-ray
tube
to
assure
uni-
form
unblanking
bias
for
all
sweep
times
and
repetition
rates.
Triggering System
The sweep can be triggered by a wide range
of triggering voltages either derived internally
from the signal to be displayed, or through a
front-panel connector from an external source.
The circuit permits the sweep to be triggered
from any selected point along the triggering
waveform. A recurrent triggering arrangement
which runs at a fifty-cycle repetition rate will
synchronize with repetitive trigger signals from
sixty cycles to two megacycles.
PAGE 1-1

Horizontal-Deflection Amplifier
A de-coupled horizontal-deflection amplifier
provides horizontal sensitivity of 2 volts per
centimeter to approximately 15 to 20 volts per
centimeter, continuously adjustable by means
of a ten-to-one continuously adjustable control
and a 10X and 1X switched attenuator.
Because this amplifier was designed for op-
timum performance with a sweep sawtooth, its
performance with sine waves is limited. This
sine-wave limitation can best be defined by an
amplitude-frequency product, which can be ex-
ceeded only at the expense of considerable dis-
tortion. The amplitude-frequency product is
2.4 centimeter-megacycles. Thus a full 10-
centimeters of deflection can be used at 240 kc,
and a 2.4-me sine wave can be viewed if the
amplitude is one centimeter peak-to-peak or
less. The amplifier frequency response toa sine
wave is down less than 30% at 400 kc when the
amplitude is within this limitation.
Output Waveforms Available
Front-panel connectors provide a positive-
going sawtooth, a positive gate synchronized
with the sweep, and a signal derived from the
displayed vertical signal. The calibrator pro-
vides an adjustable amplitude symmetrical
square wave with a repetition rate of about one
kilocycle, The amplitude is adjustable intwenty
steps between .2 millivolts and 100 volts.
Power Supply
All de voltages are regulated to accommodate
line-voltage variations between 105 and 125 volts
or 210 volts to 250 volts, 50 to 60 cycles, ac,
and for the differences in dc loads imposed by
the different plug-in units.
Power Consumption
At 117 or 234 volts, 475 watts with plug-
in unit in place.
Cooling
Safe operating temperature is maintained with
filtered, forced-air ventilation. A thermal dis-
connect device turns off the ac power in the
event the fan fails or the air intake becomes
blocked.
Illuminated Graticule
The graticule is accurately scribed in centi-
meters and fifths of centimeters. The scribed
lines can be edge-lighted either by white or by
red light. A green filter is supplied to increase
contrast in the presence of room brightness.
At extra cost, a light shield is available con-
structed so that it will slip onover the graticule
bezel.
Mechanical Characteristics
Construction
The cabinet and chassis are madeof electric-
ally-welded aluminum alloy.
Finish
Photo-etched anodized aluminum -alloy panel,
wrinkle-enameled cabinet.
Dimensions
24 inches long, 13 inches wide, 16-3/4 inches
high.
Weight
61-1/2 pounds.
FUNCTIONS OF FRONT-PANEL CONTROLS
AND CONNECTORS
TRIGGERING MODE (red knob)--Five-position
switch arranges trigger circuits for five
kinds of triggering: DC, AC SLOW, AC
FAST, AUTOMATIC and HF SYNC, In Type
531 instruments, S/N 101-6010 and in Type
541, S/N 101-5414, AUTOMATIC is labeled
AC AUTO, In Type 531, S/N 101-592, there
is no HF SYNC position.
PAGE 1-2
TRIGGER SLOPE--Six-position switch selects
source of trigger signal and converts to
negative-going output, either negative-going
Or positive-going input.
TRIGGER INPUT--UHF coax connector to trig-
gering circuits through EXT positions of
TRIGGER SLOPE switch.
531/541—GENERAL DESCRIPTION

STABILITY (red knob)--Contro] for adjusting
the
stability
of
the
sweep
circuits
for
a
stable
display.
The
control
has
a
PRESET
position
suitable
for
most
triggering
ap-
plications. Type 531, S/N101-6710, and
Type 541, S/N101-5942, have no PRESET
position on the STABILITY control.
TRIGGERING
LEVEL--Potentiometer
deter-
mines
part
of triggering
waveform
where
sweep
triggers.
TIME/CM-
-Eight-position
switch
selects
timing
capacitors
to
determine
sweep
speeds,
and
determine
duration
of
trigger
holdoff
period.
MULTIPLIER-
-Six-position
switch.
Three
po-
sitions
place
precision
charging
resistors
in
series
with
timing
capacitors
to
determine
sweep
speeds
in
conjunction
with
selected
timing
capacitor.
Three
positions
, marked
in
red,
place
adjustable
charging
voltages
in
series
with
timing
capacitors
for
contin-
uous
control
of
sweep
speeds.
5X
MAGNIFIER--Two-position
switch
removes
or
inserts
feedback
in
sweep
amplifier
to
change
sweep
speeds
by
a
factor
of
five.
HORIZONTAL
DISPLAY--Three-position
switch
connects
sweep
amplifier
to
internal
sweep
generator
in
one position,
or to front
panel
connector
directly
or
through
10-1
fixed
attenuator
in second
and
third
positions.
EXTERNAL
SWEEP
ATTENUATOR,
10-1---
Continuously
adjustable gain
control on
hor-
izontal
amplifier.
Switched
out
of
circuit
for
internal sweeps.
EXTERNAL
SWEEP
IN--Front-panel
connector
to
horizontal
amplifier
through
HORIZON-
TAL
DISPLAY
switch.
Magnifier
must
be
switched
to
ON
for
undistorted
10-cm
deflection.
VERT.
SIG.
OUT--Front-panel
connector
sup-
plies
signal
from
vertical
amplifier
via
trigger
cathode
follower.
HORIZONTAL POSITION-- Positions trace along
horizontal axis.
al
531/541—-GENERAL DESCRIPTION
VERNIER (red knob)- -Fine adjustments of hori-
zontal positioning, with five times the reso-
lution of the coarse adjustment.
SQUARE-WAVE
CALIBRATOR
(red
knob)---
-
Three-position
switch turns
on
calibrator
plate
voltage
and
switches
in
or
out
1000-
to-1
voltage
divider
to
give
either
volts
or
millivolts
output.
SQUARE-WAVE
CALIBRATOR
(black
knob)---
Nine-position
switch
selects
nine
taps
on
precision
voltage
divider
in
calibrator
cir-
cuit.
Provides accurate
voltages
of .2, .5,
1,
2, 5, 10,
20,
50, and
100 volts
in VOLTS
position,
or millivolts
in the MILLIVOLTS
position
of
the
red
concentric
control
knob.
CAL OUT---UHF coax front-panel connector
from the calibrator.
+GATE
OUT---Front-panel
binding
post
sup-
plies
positive
20-volt
square
pulse,
dc-cou-
pled
through cathode
follower
,
synchronized
with
the
internal
sweep.
SAWTOOTH
OUT---Front-panel
binding
post
supplies
150-volt
positive-going
sawtooth
dc-coupled
through
cathode
follower,
syn-
chrenized
with
the
internal
sweep.
POWER---On-off
switch
in
primary
of
power
transformer
and
ventilating-fan
lead.
FOCUS--
Adjustable
voltage
for
the
cathode-ray
tube
focusing
grid.
INTENSITY--Bias
adjustment
to
cathode-ray
control
grid.
ASTIGMATISM-
Adjustable
voltage
for the
astig-
matism
grid
of
the
cathode-ray
tube.
SCALE
ILLUM-
-Adjustable
series
resistor
con-
trols
voltage
across
graticule
lights.
Beam-
position
indicators,
unlabeled,
marked
with
arrows.
Thé
arrow
nearest
the
illuminated
indicator
shows
which
way
the
beam
is
off
the
screen
if
it
cannot
be
seen.
Rear of Cabinet
CRT CATHODE--Binding post connects to crt
cathode through high-voltage capacitor. In-
put impedance 8 k to 15 k. Discharge
time eonstant about 15 milliseconds.
PAGE 1-3

SECTION 2
OPERATING INSTRUCTIONS
PRELIMINARY INSTRUCTIONS
Cooling
The Oscilloscope is cooled by filtered, forced-
air ventilation. The instrument must therefore
be
placed
so
the
air
intake
is
not
blocked,
and
the filter must be clean enough to permit ade-
quate air circulation. If the interior tempera-
ture does rise too high for some reason, a
thermal cutout switch will disconnect the power
and keep it disconnected until the temperature
drops to a safe value.
Time-Delay DC Power Relay
A time-delay relay delays application of the
rectified dc to the circuits long enough for all
heaters to reach operating temperature. The
time delay is approximately 25 seconds, If you
switch the ac power off, even briefly, the time-
delay relay will delay reapplication of the dc.
Cathode-Ray Tube Controls
The Tektronix cathode-ray tube inthis instru-
ment has a total accelerating voltage of 10,000
volts. The spot intensity with this amount of
acceleration can be bright enough to damage the
screen in a short time if the spot is left in one
place. Be careful not to leave a fixed bright
spot or slow sweep on the screen. Turn the
INTENSITY control counterclockwise so that
the spot is dim whenever you leave the instru-
ment unattended.
The separate FOCUS, ASTIGMATISM and IN-
TENSITY controls are somewhat interdependent,
and may require readjustment for different IN-
TENSITY control settings.
Illuminated Graticule
The adjustable graticule lighting control la-
beled SCALE ILLUM., can be adjusted to suit
the lighting conditions of the room. Thecolored
filter supplied is colored to provide the maximum
trace contrast for the P2 phosphor in the pres-
ence of room light.
The graticule is accurately scribed in centi-
meters and fifths of centimeters. These scale
markings and the calibrated fixed vertical-de-
flection sensitivities and sweep times, can be
used to convert deflections in centimeters into
volts and seconds. Vertical sensitivities are
calibrated in volts per centimeter, and hori-
zontal sweep-times are calibrated in seconds per
centimeter, which, if multiplied by centimeters
of deflection, give volts and seconds.
The graticule can be mounted in either of two
positions rotated 180 degrees from each other.
In one position, the graticule illumination is
colored red, and in the other position in white.
The white will reproduce well photographically.
FIRST-TIME OPERATION
First get atrace onthe screen by the simplest
method, and then proceed with the presentation
you want after you get an idea of the functions
of the controls To get a simple trace on the
screen,
insert
a
preamplifier,
and
proceed
as
follows:
Turn the POWER switch to OFF. Connect the
power
cord
toa
source
of
117-volt,60-cycle
pow-
er. Then set the front-panel controls as follows:
INTENSITY
Counterclockwise (CCW)
FOCUS
eo
Center
531/541-OPERATING INSTRUCTIONS
ASTIGMATISM
Center
POWER
ON
TRIGGERING LEVEL
CCW
STABILITY (red knob)
PRESET or CCW
TRIGGER SLOPE
+ INT
PAGE 2-1

TRIGGERING MODE (red)
Connect a lead between the CAL, OUT ter-
AUTOMATIC or AC AUTO minal and the INPUT terminal of the unit. Set
TIME/CM
100 MICRO SEC
MULTIPLIER
2
HORIZONTAL DISPLAY
INTERNAL SWEEP
HORIZONTAL POSITION
Center
SQUARE-WAVE CALIBRATOR
5
VOLTS, MILLIVOLTS, OFF
VOLTS
the controls of the plug-in as follows:
AC--DC AC.
VOLTS/CM 2
VARIABLE Clockwise
VERTICAL POSITION Center
When
the
POWER
switch
has
been
turned
on
for
about
one
minute,
turn
the
INTENSITY
control
clockwise
until
you
can
see
a
trace
on
the
screen.
With
the
calibrator
waveform
dis-
played,
you
can
set
the
FOCUS,
INTENSITY
,
and
ASTIGMATISM
controls
for
a
sharp
line,
and
position
the
trace
near
the
screen
center
with
the
HORIZONTAL
POSITION
and
VERTICAL
POSITION
controls.
TRIGGERING MODES
Automatic
You
are
now
displaying
the
calibrator
wave-
form,
whose
repetition
rate
is
about
one
kilo-
cycle,
and
whose
amplitude
is
five
volts,
peak-
to-peak,
with
the
AUTOMATIC
mode
of
trigger-
ing.
This
is
about
the
simplest
mode
of
trigger-
ing.
It
is
useful
for
general
purpose
viewing,
and
will
operate
satisfactorily
for
a
wide
variety
of
trigger
signals
whose
repetition
rates
are
be-
tween
sixty
cycles
and
about
two
megacycles.
AC Slow
When
you
have
a
good,
well-focused
trace
of
the
calibrating
waveform
by
the
AUTOMATIC
mode
of
triggering,
try
the
other
four
TRIG-
GERING
MODE
switch
positions.
Turn
the
switch
to
the
AC
SLOW
position.
Advance
the
TRIGGERING
LEVEL
control
clockwise
until
you
getastable
trace
again.
There
may
be
a
con-
siderable
range
of
the
LEVEL
control
over
which
you
can
get
a
stabletrace,and
the
start
of
the
trace
will
move
up
and
down
the
edge
of
the
square
wave
within
this
range.
Notice
that
the
trace
starts
on
the
upgoing
partof
the
calibrator
square
wave.
Now
turn
the
TRIGGER
SLOPE
switch
to
the
-INT
position,
and
readjust
the
TRIGGER-
ING
LEVEL
to
obtain
a
stable
trace
again.
No-
tice
now
that
the
trace
starts
on
the
down-going
portion
of
the
trace
and
that
the
position
of
the
PAGE 2-2
start
can
again
be
changed
somewhat
with
the
LEVEL
control.
DC Triggering
Now turn the TRIGGERING MODE switch to
DC,
Adjust
the
LEVEL
control
for
stable
trig-
gering,
and
then
position
the
trace
with
the
VERTICAL
positioning
control.
You
will
notice
that
triggering
occurs
at
a
vertical
level
on
the
screen
selected
by
the
LEVEL
control
and
that
the
triggering
point
changes
relative
to
the
waveform
as
the
waveform
is
positioned
verti-
cally.
This
effect
will
be
more
noticeable
if
you
look
at
a
low-frequency
sine
wave.
This
triggering
position
is
most
useful
for
low-frequency
signals.
Ir
is
not
suitable
for
applications
where
the
de
level
is
changing
such
as
when
a
Dual-Trace
Unit
is
being
used.
AC Fast
In
the
AC
FAST
position
of
the
TRIGGERING
MODE
switch,
the
circuit
is
quite
similar
to
that
in
the
AC
SLOW
position,
and
you
will
notice
no
difference
when
displaying
the
cali-
brator
waveform.
The
only
difference
is
thatan
re
filter
is
inserted
in
the
circuit,
making
it
insensitive
to
low
frequencies,
and
allowing
it
to
recover
quickly
from
de
level
changes.
This
is
the
position
to
use
when
there
is
hum
present.
This
is
also
the
best
position
to
use
with
the
mn
531/541-OPERATING INSTRUCTIONS

alternate
sweep
feature
of
the
53/54C
unit
if
you
use
INTernal
triggering
with
signals
having
fre-
quency
components
above
10
kc.
HF Sync
The HF SYNC position of the TRIGGERING
TRIGGERING
Triggering Level
The TRIGGERING LEVEL control selects the
point
on
the
triggering
waveform
at
which
trig-
gering will occur. To trigger on small signals
this
control
must
be
set
near
O,
or
near
the
dc
level with dc triggering. The levels are indi-
cated on the panel as positive to the right and
negative
to
the
left.
Negative
positions
of
the
LEVEL
control
cause
triggering
to
occur
dur-
ing
negative
levels
of
the
triggering
waveform
and
positive
positions
cause
triggering
during
positive levels. This control is not used in the
AUTOMATIC
and
HF
SYNC
positions
of
the
TRIGGERING MODE switch.
Trigger Slope
The
+
positions
of
the
TRIGGERSLOPE
switch
(black
knob)
cause
triggering
to
occur
during
the
rising
portion
of
the
triggering
waveform.
The
level
may
be
either
negative
or
positive.
The
-
positions
cause
triggering
to
occur
during
the
falling
portion
of
the
waveform.
Thus
for
slow
rising
waveforms
such
as
sine
waves,
the
triggering
point
can
be
caused
to
occur
at
almost
any
point
in
the
waveform.
An
additional
function
of
the
TRIGGERSLOPE
switch
selects
the
source
of
trigger
signals.
For
each
of
the
available
signal
sources,
the
switch
provides
a
choice
of
positive
or
negative
slope.
Triggering Mode
The
TRIGGERING
MODE
switch
arranges
the
circuits
to
provide
the
kind
of
triggering
you
need.
This
is
the
red
knob
and
the
positions
it
selects
are
labeled
in
red
on
the
panel.
Slowly
changing
waveforms
work
best
on
the
AC
SLOW
and
DC
positions.
In
the
AC
SLOW
position
a
capacitor
removes
the
dc
component
of
the
triggering
waveform
and
makes
triggering
on
the
vertical
signal
independent
of
trace
posi-
a
531/541—-OPERATING INSTRUCTIONS
MODE
switch
is
primarily
for
signals
having
a
repetition
rate
in
excess
of
ten
megacycles.
In
this
position
the
sweep
will
trigger poorly,
if
at
all,
on
the
calibrator
waveform.
To
trigger
on
a
high-frequency
signal,
simply
advance
the
STABILITY
control
until
a
stable
trace
is
ob-
tained.
The
LEVEL
control
is
not
used
in
this
position.
INSTRUCTIONS
tion.
This
position
is
suitable
for
signals
from
twenty
cycles
up to
about
five
or ten
megacycles.
The
DC
position
is the
same
except
that
it
re-
sponds
to
dc
as well.
In
the
AC
FAST
position,
the
circuit
includes
an
rc
filter,
useful
for
pre-
venting
60-cycle,
or
other
low-frequency
com-
ponents,
from
triggering
the
sweep
when
both
high-
and
low-frequency
components
are
present
in
the
triggering
waveform.
The
low-frequency
limit
is
about
two
kilocycles.
In
these three
positions,
if
the
STABILITY
control
is
properly
set,
the
sweep
will
not
run
unless
triggered
by
a
signal.
The AUTOMATIC and HF SYNC switch posi-
tions both arrange synchronizing circuits rather
than strictly triggering circuits. The AUTO-
MATIC
circuit
provides
a
free-running
multi-
vibrator with a normal repetition rate of about
50
cycles,
which
locks
in
and
runs
synchro-
nously
with
recurrent
triggering
waveforms
from
60
cycles
to
about
2
megacycles.
The
synchronized
multivibrator
then
triggers
the
sweep-gating multivibrator,
The
HF
SYNC
switch
setting
arranges
a
cir-
cuit
which
connects
the
triggering
source
di-
rectly
to
the
sweep-gating
multivibrator
so
that
it
can
synchronize
with
the
triggering
wave-
form.
The
sweep-gating
multivibrator
must
be
free-running
for
this
type
of
operation.
It
free-
runs
at
advanced
settings
of
the
STABILITY
control.
It
will
synchronize
with
signals
whose
frequencies
are
as
high
as
30
megacycles,
ata
sweep-repetiton:
rate
up
to
200
kilocycles.
Stability
The
STABILITY
control
adjusts
bias
level
on
the
sweep-gating
multivibrator
near
the
level
at
which
it
will
free-run.
Three
principal
settings
of
the
STABILITY
control
are
used,
the
first
setting
is
with
the
control
advanced
to
the
right,
just
past
the
point
where
the
sweep-gating
mul-
tivibrator
free-runs;
second,
retarded
to
the
left
PAGE 2-3

about 5 or 10 degrees from the point where
free-running ceases; and third, retarded all the
way left, to make the multivibrator inoperative.
For synchronized operation of the sweep-gat-
ing multivibrator, as used in the HF SYNC posi-
tion, set the STABILITY control to the advanced
position so that the sweep just free-runs, and
keep it to the right of this point while adjusting
its position to synchronize the sweep,
For all triggered modes of operation, except
AUTOMATIC, the STABILITY control should be
retarded 5 to 10 degrees to the left of the free-
run point. In the AUTOMATIC mode and when
the STABILITY control is turned to the PRE-
SET position, the STABILITY control is replaced
by an internal contro! which has been preset to
give reliable triggering for most applications.
SWEEP OPERATION
Time/Cm and Multiplier
These controls determine the speed of the
horizontal trace. The time per centimeter of
horizontal deflection is equal to the product of
the MULTIPLIER setting and the TIME/CM
setting. Times per centimeter from .1 micro-
second to 1 second in steps of lO can be selected
with the TIME/CM switch, and accurate, fixed
multipliers of 1, 2, and 5 times can be selected
with the MULTIPLIER switch, The sweeptimes
so selected can be depended on within three
per cent of their indicated value. The variable
sweep time positions can be checked at the
limits of the 2.5-to-1 times, and 5-to-2 times
positions against the accurate fixed multipliers
to improve their accuracy.
Magnifier
This control inserts or removes a feedback
network in the sweep amplifier that changes the
gain five times. The linearity of the amplifier is
somewhat better when the feedback circuit is
included. The center one fifth of thetraceis ex-
tended to fill the graticule when the magnifier is
switched on. When you use the sweep magnifier
to realize the fastest sweep time, .02 microsec-
onds per centimeter, the linearity is reduced
from three per cent to aboutfive percent. With
a constant repetition rate of triggering you will
need to increase the INTENSITY control settings
as you decrease the TIME/CM control settings
because of the reduced duty cycle.
External Sweep
In the X10 and X1 positions of the HORI-
AUXILIARY
Square-Wave Calibrator
Accuracy of the open-circuit voltage of the
PAGE 2-4
ZONTAL DISPLAY switch, the EXTERNAL
SWEEP IN binding post is connected to the
horizontal amplifier. In both of these posi-
tions you must switch the 5X MAGNIFIER
switch to ON to keep the input amplifier within
its linear range. It will be necessary to ad-
vance the INTENSITY control because the un-
blanking pulse is not present if the sweep is not
running.
The variable EXTERNAL SWEEP ATTENUA-
TOR, 10-1 can be used in conjunction with the
X10 and X1 positions of the HORIZONTAL DIS-
PLAY switch to obtain continuous coverage of
the 100-1 attenuation range. Because the ampli-
fier is dc-coupled, a large dc component in
the signal being viewed may position the trace
off the screen and make it impossible to center
the display with the HORIZONTAL POSITION
control.
Because this amplifier was designed for op-
timum performance with a sweep sawtooth, its
performance with sine waves is limited. This
sine-wave limitation can best be defined by an
amplitude-frequency product, which can be ex-
ceeded only at the expense of considerable dis-
tortion. The amplitude-frequency product is
2.4 centimeter-megacycles, Thus a full 10 centi-
meters of deflection can be usedat 240 kc, and a
2.4-me sine wave can be viewed if the amplitude
is one centimeter peak-to-peak or less. The
amplifier frequency response to a sine wave is
down less than 30% at 400 kc whenthe amplitude
is within this limitation.
FUNCTIONS
calibrator is within 3 per cent of the indicated
voltage. However, since the output impedance
at the CAL. OUTterminal varices with the setting
531/541—-OPERATING INSTRUCTIONS

of the voltage-selector switch, you must be
careful that the load impedance you connect it
to does not change the output voltage. The out-
put impedance varies between about 100 ohms
over the millivolt range to about 500 ohms at
the 50-volt tap. Except at the 100-volt tap, the
output voltage depends on the division ratio of
a voltage divider. Any appreciable change in
impedance of the shunt leg of the divider will
therefore reduce the output approximately in
proportion to the reduction of impedance. The
l-megohm input impedance of the oscilloscope
will cause no appreciable change in voltage at
any setting of the selector switch. At the 100-
volt tap, the out impedance is that of the cath-
ode follower, about 250 ohms.
The rising portion of the calibrator waveform
follows an rc curve with a time constant such
that it requires about | microsecond to reach
90 per cent of peak. Millivolt settings provide
a slightly better risetime of about 0.7 micro-
seconds, and the worst case is the 50-volt set-
ting with about 1.5 microseconds to the 90 per
cent point. Reactive loads will affect these times.
The frequency of the calibrator multivibrator
is nominally 1000 cycles, but may vary 30 per
cent either way. Do not use it for more than a
rough check of sweep-timing accuracy.
Trace-Brightness Modulation
To couple time markers into the cathode cir-
cuit for brightness modulation, disconnect the
ground strap at the rear of the instrument and
connect the source of modulating voltage to the
CRT
CATHODE
post.
A
peak-to-peak
voltage
of
about
50
volts
is
required
to
turn
the
beam
on
and
off.
Input
impedance
is
8
k
to
15k,
depending on the INTENSITY contro] setting.
The circuit is ac-coupled through a high-voltage
capacitor, discharge time constant about 15
milliseconds.
Direct Connection to Deflection Plates
A plastic plate and mounting bracket are
available from the factory for making direct
connections to the crt vertical-deflection plates.
The mounting bracket is designed to clamp
around the neck of the crt shield, adjacent to the
deflection-plate connections. When mounted
correctly, the plate will be accessible through the
ert deflection-plate access hole in the left side-
panel. The bracket and plate may be ordered
with or without the necessary parts for verti-
cal-positioning voltages. Specify part number
013-008 for the unwired unit, or part number
013-007 for the wired unit. Holes can be drilled
in the plastic plate for mounting coaxial or
other connectors. The two pins on the left-hand
side of the crt neck are the vertical-deflection
plates.
To avoid distortion, the average dc potential
on the vertical-deflection plates should be 300
volts. If you use a different voltage, the dis-
tortion can be minimized by adjusting the GEOM.
ADJ. control at the rear of the sweep chassis.
Unless dc coupling is required, connect coup-
ling capacitors in series with the leads tothe de-
flection plates and connect one-megohm resis -
tors from the deflection plates to the leads from
the vertical amplifier. With this connection the
plates are maintained at the proper operating
potential, and positioning control is retained for
the front-panel VERTICAL POSITION control.
Vertical Signal Out
The signal applied to the vertical amplifier
is available at the front-panel VERT. SIG. OUT
binding post. A signal which will cause one centi-
meter of deflection will producea signal of about
two volts, peak-to-peak, at the binding post.
The signal is applied to the binding post ata
relatively
low
impedance
from
a
cathode
fol-
lower.
The
passband
is
dependent
on
the
exter
-
nal load. With a one megohm resistor shunted
by
a
50
wuf
capacitor
as
a
load,
it
extends
from
about 20 cycles to 4.5 megacycles at the 3 db
points. Without the capacitive load the high-
frequency 3-db point is extended to about 6
megacycles.
SIMPLIFIED SWEEP DIAGRAMS
The
trigger
signal
is
normally
coupled
to
the
multivibrator
by
way
of
the
trigger
amplifier.
The
trigger
signal
trips
the
multivibrator,
which
sends
a
negative
gate
through
the
disconnect
diodes
to
two
points
on
the
sweep
generator.
ad
531/541—-OPERATING INSTRUCTIONS
The sweep generator makes a positive-going
sawtooth that is amplified and used to sweep the
beam across the cathode-ray tube.
The speed of the sawtooth depends on the
PAGE 2—5

capacitance of the timing capacitor and the re-
sistance of the charging resistor. The height of
the sawtooth depends on the setting of the sweep
length adjustment. A portion of the sawtooth
voltage is coupled back to the multivibrator con-
trol grid via the sweep-length and holdoff tubes,
where it reverts the multivibrator and turns the
sawtooth generator off.
Quiescent bias on the multivibrator is deter-
mined by the dc level of the stability cathode
follower, which depends on the STABILITY
control setting. The purpose of this control is
to set the multivibrator bias near enough to
triggering that the input trigger will trigger it.
If the bias is lowered still further, the multivi-
PAGE 2-6
brator will trigger itself again as soon as it is
reverted, and will run recurrently.
Although the STABILITY control is mounted
concentrically with the TRIGGERING LEVEL
control, it works only on the sweep generator,
and is not involved in the triggering circuits.
The purpose of the STABILITY control is to
place the grid of the normally-conducting left-
hand multivibrator near enough to cutoff that
the negative trigger signal from the regenerative
trigger shaper can drive the tube to cutoff. The
control therefore requires only one adjustment to
make the multivibrator responsive to that size
of trigger. The multivibrator turns the sweep
generator on when it is triggered.
531/541—OPERATING INSTRUCTIONS

SECTION 3
CIRCUIT DESCRIPTION
BLOCK DIAGRAM
The Block Diagram shows interconnections of the functional
parts of the oscilloscope, except the power supplies. Functions
of the switches are shown instead of their actual connections.
Plug-In Preamplifiers
In the upper left of the Block Diagram is
shown the vertical-deflection system. The block
labeled " Plug-Ins" represents one of the plug-in
preamplifiers available. Connections for power
in and signal-out are made through a multiple-
contact mating plug and socket. Output from
these units is push-pull at low impedance.
Main-Unit Amplifier
The main-unit amplifier amplifies the signal
and drives the delay line which terminates in
the vertical deflection plates. The trigger pick-
off circuits obtain a sample ofthe vertical signal
for triggering the sweep,
Delay Line
In the Type 531, the balanced 24-section
lumped-section delay line adds 1/4 microsecond
of delay to the signal so that the sweep circuits
will have time to get the cathode-ray spot un-
blanked
and
sweeping
before
the
signal
reaches
the vertical-deflection plates.
In the Type 541, a balanced 50-section delay
line adds .2 microseconds of delay for sweep
unblanking purposes.
Trigger Cathode Followers
The trigger signal from the main-unit ampli-
fier passes through two cathode followers. The
first applies the signal at low impedance to the
trigger amplifier and the second connects to the
front-panel VERT. SIG, OUT binding post.
Trigger Amplifier
The trigger amplifier provides either in-phase
Ger
531/541—CI RCUIT DESCRIPTION
or inverted output in order to provide negative-
going output for either negative-going or posi-
tive-going input trigger signals.
Trigger Shaper
The trigger-shaper amplifier makes a sharp
pulse from the trigger signal at a time during
the sloping part of the trigger signal determined
by the setting of the triggering-level control. A
sharpened negative-going pulse triggers the
multivibrator.
Multivibrator
The multivibrator turns on the sweep genera-
tor and generates the crt-tube unblanking pulse
when it is switched from its quiescent state. The
sharp negative-going trigger signal from the
trigger-shaper circuit trips the multivibrator,
which thereafter stays in the second state until
the sweep generator reverts it to its quiescent
state.
Sweep Generator
The sweep generator is a Miller integrator
that
produces
a
positive-going
sawtooth
about
150
volts
peak-to-peak.
The
sweep
generator
turns
itself
off
when
it
reaches
a
prescribed
level
determined
by
the
sweep-length
control,
by
transmitting
a
signal
through
the
trigger-hold-
off circuits to the multivibrator.
Trigger Holdoff
The
trigger-holdoff
circuit
transmits
the
sweep
turn-off
signal
to
the
multivibrator
but
briefly
holds
off
subsequent
trigger
signals
from
starting
the
sweep
again
until
all
parts
of
the
circuit
have
reached
their
quiescent
states.
PAGE 3-1

Sweep Amplifier
The sweep amplifier converts the sawtooth
output of the sweep generator into push-pull
Output at low impedance at the level required
to sweep the beam across the crt-tube screen.
The amplifier gain can be increased by a factor
of five for sweep magnification. The horizontal-
positioning control operates on this stage.
Unblanking
The multivibrator generates the positive-
going unblanking pulse at the same time itturns
on the sweep generator. The positive pulse is
transmitted by means of two cathode followers
through a floating high-negative-voltage supply
to the control grid of the crt tube.
POWER
Plate and Heater Power
The 60-cycle 117/234-volt transformer has
five separate high-voltage windings. AC output
from each winding is rectified through separate
bridge-connected full-wave selenium rectifiers.
Rectified dc output is filtered with capacitors
and regulated by means of series-regulator
tubes. Four positive-voltage supplies giving 100
volts, 225 volts, 350 volts and 500 volts, are
all referred to the negative 150-volt supply for
regulation. The negative 150-volt supply is re-
ferred to a gas regulator tube.
Seven heater windings on the same trans-
former furnish heater voltage to all tubes using
ac in the main unit and the plug-in units. Two
of these windings are also used to supply a sel-
enium bridge rectifier which supplies dc voltage
for the delay-line driver tubes.
External Sweep Amplifier
The external sweep amplifier provides a
means of using external sweep voltage. It
includes a fixed attenuator and an adjustable at-
tenuation control. Choice of internalor external
sweep can be made by means of the HORIZONTAL
DISPLAY switch. The sweep magnifier must
be used with external sweeps.
Calibrator
The calibrator has no internal connection to
the vertical amplifier system. It consists of a
symmetrical multivibrator with a cathode-fol-
lower output tube whose cathode resistor is a
calibrated voltage divider.
SUPPLY
Cathode-Ray Tube High-Voltage
A 60-ke vacuum-tube oscillator has the pri-
mary of a step-up transformer for its oscillator
inductance. A sample of the rectified secondary
voltage is compared to a stable dc source, and
the difference is kept constant by an electronic
circuit that adjusts the oscillator amplitude of
oscillation in the direction to reduce any change.
A voltage tripler vacuum-tube rectifier pro-
vides positive 8650 volts for the post-deflection
acceleration electrode of the crttube. Twonega-
tive supplies, insulated from each other, supply
the crt-tube cathode at -1350 volts and control
grid at -1450 volts. The control-grid supply is
free to assume a voltage 1550 volts more
negative than its positive terminal. The positive
terminal is raised more positive by the positive
unblanking pulse and the negative terminal and
ert-tube control grid therefore also follow the
same positive pulse 1550 volts below.
VERTICAL-DEFLECTION SYSTEM
GENERAL
In the Type 531, the de-coupled, push-pull
main Vertical Amplifier provides the necessary
gain to drive the Delay Line and the vertical
deflection plates of the crt. The main units of
the Vertical Amplifier in Serial Numbers 101
through 7600 are the Input Amplifier and Delay
Line Driver stage, V508 and V509; the Delay
Line Output Cathode Followers, V558A and
PAGE 3-2
V558B, the Output Amplifiers, V570 and V580
and the Output Cathode Followers, V606A and
B, The other circuits are the Internal Trigger
Amplifier, V527, the Internal-Trigger Cathode
Follower, V535A and the Vertical-Signal-Out
Cathode Follower, V535B.
In Serial Numbers 7601 and up, the Vertical
Amplifier Main Units are the Input Ampli-
fier stage V504 and V524, the Driver Cathode
531/541—CI RCUI T DESCRIPTION "S

Follower stage, V533B and V543B, and the Out-
put
Amplifier
stage
V554
and
V564.
Other
cir-
cuits
in
this
serial
number
range
are
the
Trigger Pickoff Amplifier V584, the Trigger
Cathode
Follower,
V593A,
the
Vert.
Sig.
Out
Cathode
Follower,
V593B,
and
the
Indicator
Amplifier and Lamps V533A and B536A, and
V543A and B546, respectively.
Vertical Amplifier Circuit Details
Type 531, S/N 101-7600
In Type 531, S/N 101 through 7600, signal in-
put from the plug-in units is connected through
terminals 1 and 3 to the grids of input ampli-
fiers V508 and V509. The cathodes of these two
tubes
are
connected
through
a
degenerative
rc
network,
R502,
R503,
R504
and
C503.
This
net-
work lowers the amplifier gain about two per
cent
except
during
the
first
1/4
microsecond
for
a step signal, to compensate tor a response
characteristic of cathode followevs used else-
where in the vertical amplifier system.
Delay Line
The 24-section,1/4-microsecond delay line
introduces an additional 1/4 microsecond of
delay
to
permit
the
sweep
generator
and
unblank-
ing circuits to get going before the triggering
signal gets to the deflection plates, so that the
leading edge of the signal can be observed. The
triggering signal is taken push-pull from the
mid-point of the first delay-line section so
that
the
capacitance
of
the
grids
of
trigger
amplifiers
V527A
and
V527B
can
be
part
of
the
delay-line
shunt
capacitance,
The
line
is
termi-
nated
by
R938
and
R940,
with
C938
and
©940
to
correct
the
phase
angle
of
the
terminating
impedance.
Output
is
taken
from
the
mid-point
of the last delay-line section so that the input
capacitance
of
cathode
followers
V558A
and
V558B
can
be
part
of
the
line
shunt
capacitance.
Delay-Line Output Cathode Followers
Cathode
output
from
V558A
and
V558B
is
connected
through
peaking
coils
L557
and
L558
to
the
grids
of
V570
and
V580,
Gainof
this
stage
can
be
adjusted
over
a
smal]
range
by
an
internal
screwdriver
adjustment,
R574,
labeled
AMPL
GAIN,
which
adjusts
the
amount
of
degeneration
in
the
common-cathode
circuit.
L570
and
L580
are
adjustable
peaking
coils.
531/541—CIRCUIT DESCRIPTION
DC -Shift Compensation
A long-time-constant change in gain which
is characteristic in high-conductance stages is
compensated for by an rc network, R595, R596,
R597, C595A and C595B. A screwdriver adjust-
ment on R596, labeled DC SHIFT COMP per-
mits the amount of compensation to be adjusted
to accommodate tube differences.
Output Cathode Followers
Plate output from V570 and V580 is applied
to the vertical-deflection plates of the cathode-
ray tube through cathode followers V606A and
V606B, and through peaking coils L643 and L635
and damping resistors R634 and R635.
Off-Screen Trace Indicator
Neon glow lamps B628 and B629 are con-
nected between cathodes and +225 volts. The
cathodes are somewhat higher than + 225 volts
when the spot is centered. If the cathode of
either tube rises much above this voltage so that
the
spot
is
not
visible
on
the
screen,
the
neon
glow
lamp
at
that
cathode
will
glow
and
show
which direction off the screen it is positioned.
Internal- Trigger Pickoff
Internally
derived
triggering
voltage
is
taken
from
the
vertical-deflection
signal
through
V527A
and
V527B,
which
are
connected
inorder
to
produce
single-ended
output
from
push-pull
input.
Cathode
follower
V535A
supplies
the
sig-
nal
to
the
INT.
positions
of
the
TRIGGER
SLOPE
switch. SWL.
Vertical-Signal Output
The
vertical-deflection
signal
present
at
the
internal-trigger
amplifier
is
capacitively
cou-
pled
to
the
VERT.
SIG,
OUT
binding
post
via
cathode
followers
V535A
and
V535B.
Vertical
Amplifier
Circuit
Details
Type
531,S/N7601
and
up
In
Type
531,
Serial
Numbers
7601
and
up,
the
signal
input
from
the
plug-in
unit
is
coupled
through
terminals
1
and
3
of
the
interconnecting
plug
to
the
grids
of
the
Input
Amplifier
stage.
The
plate
circuit
of
this
stage
is
compensated
for
both
high-frequency
attenuation
and
dc
shift.
PAGE 3-3

High-frequency compensation is provided by
the series-shunt peaking coils L506 and L523.
These coils extend the bandwidth of the am-
plifier by reducing the high-frequency attenua-
tion caused by the stray capacitance in the
circuit.
De shift in the amplifier tubes--a condition
whereby the dc (and extremely low-frequency)
transconductance is less than at mid-frequen-
cies--is compensated for by a de "boost" net-
work. R507 and C507A, in the plate circuit of
V504, and R524 and C507B, in the plate circuit
of V524, shunt the plate-load resistors in each
circuit. The extremely long time constant of
the circuit is such that the plate-load resistance
remains 1.8 kilohms in the range from dc to a
fraction of a cycle, but reduces in value to a
minimum of 1.77 kilohms for frequencies above
this range. The slightly higher plate-load resis -
tance, in the range from dc to a fraction of a
cycle, compensates for the slightly reduced
transconductance of the tubes in this range, so
that the gain remains substantially constant
from dc to the upper limit of the amplifier.
The Input Amplifier is coupled to the Output
stage by the Driver C.F. stage V533B and
V543B. This cathode-follower stage provides
the necessary low impedance to drive the Out-
put Amplifier. The Output Amplifier is the
driving source for the Delay Line and the verti-
cal deflection plates in the crt. The gain of
this stage is adjusted by means of R570, the
GAIN ADJ., which varies the degeneration in
the cathode circuit. This control is adjusted so
that the vertical deflection on the crt agrees
with the plug-in unit's VOLTS/CM calibration
when
the
VARIABLE
control
is
set
to
the
CALIBRATED
position.
R553
and
R563
are
the
terminating resistors for the Delay Line; they
are also the plate-load resistors for the Output
Amplifier.
Beam-Position Indicators
The beam-position indicators B536 and B546,
located on the front panel above the crt, indi-
cate the relative vertical position of the trace
with
respect
to
the
center
of
the
graticule.
When
the beam is centered vertically, the potential
across
either
neon
is
insufficient
to
light
it.
As
the
beam
is
positioned
up
or
down
the
screen,
however, the grid voltage for the Indicator Am-
plifiers,
obtained
from
a
tap
on
the
Delay
Line
terminating
resistors,
will
change.
The
current
PAGE 3-4
through one amplifier will increase, and the
current
through
the
other
will
decrease. Hence,
the
voltage
across
the
neon
will
increase,
causing
it
to
light,
and
the
voltage
across
the
other
will
decrease,
causing
it
to
remain
ex-
tinguished.
The
neon
that
lights
will
indicate
the
direction
in
which
the
beam
has
been
moved.
Trigger Pickoff
When
internal
triggering
of
the
Time
Base
Generator
is
employed
(black
TRIGGER
SLOPE
knob
in
either
the
+
or
-INT.
position),
a
"sample"
of
the
vertical
signal
is
used
to
develop
the
triggering
pulse.
This
"sample",
obtained
from
the
Driver
C.F,
stage,
is
ampli-
fied
by
the
Trigger
Pickoff
Amplifier
and
coupled
through
the
Trigger
C.F.
to
the
Time
Base
Trigger
circuit.
The
"sample"
of
the
vertical
signal
is
also
ac
coupled,
through
V593B
and
C599,
to
a
front-panel
jack
labeled
VERT.
SIG,
OUT.
Delay Line
The
output
signal
from
the
Vertical
Amplifier
is
coupled
through
the
Balanced
Delay
Line
to
the
vertical
deflection
plates
of
the
crt.
The
function
of
the
line
is
to
delay
the
arrival
of
the
waveform
at
the
deflection
plates
until
the
crt
has
been
unblanked
and
the
horizontal
sweep
started,
This
delay
insures
that
the
very"
front"
of
fast
vertical
signals
can
be
observed.
The
line
is
adjusted,
by
means
of
the
variable
capaci-
tors
connected
across
the
line,
for
optimum
transient
response.
Type
541
Vertical
Deflection
System
General
The
dc-coupled,
push-pull,
main
Vertical
Am-
plifier
provides
the
necessary
gain
to
drive
the
Delay
Line
and
the
vertical
deflection
plates
of
the
crt.
In
Type541
Seria]
Numbers
101
through
6474,
the
main
units
of
the
Vertical
Amplifier
are
the
Input
Amplifier
Stage
V1025B
and
V1040B,
the
cathode
follower
stages
VI050
and
V1052,
and
the
6-section
Distributed
Amplifier
Output
stage.
Other
circuits
of
importance
are
the
Balance
Amplifier,
V1060,
the
Internal
Trigger
Ampli-
fier,
V1066,
Internal
Trigger
C.F.,V1052B,
Ver-
tical
Signal
Out
C.F.,
VLOSOB,
and
the
Indicator
Amplifiers
and
Lamps, V1025A
and
B1010
and
V1040A and B1014, respectively.
oad
531/541-C!I RCUIT DESCRIPTION

In
Type
541,
Serial
Numbers
6475
and
up,
the
main
units
are
Input
Amplifier
Stage
V1014
and
V1024,
cathode
follower
stages
V1033
and
V1043,
plus
the
6-section
Distributed
Amplifier
output
stage.
Other
important
circuits
are
the
Trigger
Pickoff
Amplifier
,
V1064
and
V1054,
the
Trigger
Pickoff
C.F.
V1223A,
and
Indicator
Amplifiers
and
Lamps,
V1084A
and
B1083,
and
V1084B
and
B1087,
respectively.
In
all
Type
541
instruments,
the
vertical
amplifier
has
separate
preamplifier
units
that
can
be
plugged
into
the
main
unit.
These
units
provide
a
variety
of
passbands
and
sensitivities
and
allow
for
future
developments
in
preamp-
lifiers.
The
plug-in
units
develop
balanced
push-
pull
output
which
is
maintained
push
pull
through
-
out
the
remainder
of
the
amplifier.
The
units
contain
sensitivity
adjustments
and
positioning
controls.
VERTICAL
AMPLIFIER
CIRCUIT
DETAILS
Type
541,
S/N
101
through
6474
In
Type
541,
Serial
Numbers
101
through
6474,
signal
input
from
the
preamp
is
connected
through
terminals
1
and
3
to
the
grids
of
input
amplifiers
V1025B
and
V1040B.
Thecathodes
of
these
two
tubes
are
connected
together
through
the
degenerative
network,
R1026,
R1027
and
R1028.
R1027
labeled
GAIN
ADJ.
is
variable
to
allow
the
amplifier
gain
to
be
varied
over
a
small
range.
1.1022
and
1.1041
provide
series
peaking
for
the
stage.
Triodes
VI0SOA
and
V1052A
provide
the
low
impedance
necessary
for
driving
the
distributed-amplifier
grid
line.
Beam-Position Indicators
Triodes
V1025A
and
V1040A
have
as
their
plate
loads
neon
glow
lamps
B1010
and
B1014
across
1-megohm
resistors.
When
the
trace
is
centered,
the
plate
current
is
insufficient
to
ignite
these
lamps,
but
as
the
trace
is
positioned
off
the
screen
vertically
the
current
through
one
triode
will
increase
causing
the
corresponding
lamp
to
glow
showing
which
way
the
trace
is
off
the
screen.
Trigger Pickoff
The
trigger
pickoff
tubes,
V1060
and
V1066,
convert
the
push-pull
vertical
signal
on
the
dis-
tributed-amplifier
grid
lines
to
single-ended
output
without
disrupting
the
balanced
configura-
tion
of
the
grid
lines.
The
trigger
cathode
fol-
531/541—CI RCUIT DESCRI PTION
lower supplies the amplified vertical signal at
low
impedance
to
the
oscilloscope
trigger
cir-
cuits
and
to
the
vertical-signal-out
cathode
fol-
lower.
This
cathode
follower
applies
a
sample
of
the
vertical
signal,
somewhat
limited
in
pass-
band,
to
the
front-panel
binding
post
labeled
VERT. SIG, OUT.
DC-Shift Compensation
DC-shift
compensation
is
accomplished
in
two
ways
and
corrects
for
two
different
time
con-
stants.
The
series
combination
of
R1080
and
C1045B
on
plate
line
L1080,
and
R1084
and
C1050B
on
plate
line
L1083,
lowers
the
termina
-
tion
resistance
of
these
lines
to
all
but the
very
low
frequencies.
They
provide
a
time
con-
stant
which
corrects
for
the
initial
dc
shift
in
the
amplifier.
The
second
time
constant
is
corrected
by
R1045
and
C1045A
and
R1OSO
and
C1050A.
These
rc
networks
have
a
negligible
loading
effect
on
the
distributed-amplifier
plate
lines,
but
provide
low-frequency
positive
feed-
back
to
the
input-amplifier
plates.
This
feed-
back
corrects
for the
longer-time-constant
dc
shift.
R1059,
labeted
DC
SHIFT
COMP.
permits
the
amount
of
compensation
to
be
adjusted
to
accommodate
tube
differences.
Distributed Amplifier
The
output
amplifier
is
a
six-section,
bal-
anced,
distributed
amplifier.
The
grid
lines
are
driven
by
VLOSOA
and
V1052A
through
re
fre-
quency
-compensating
networks.
The
plate
lines,
L1080
and
L1083,
drive
the
delay
line
directly.
Each
section
of
the
plate
lines
is
tuned
for
op-
timum
response
to
a
square
wave
by
trimmers
connected
line-to-line.
Termination Network
Unless
the
plate
lines
are
terminated
at
the
reverse
end
with
a
resistance
equal
to
their
characteristic
impedance,
signals
traveling
the
reverse
direction
down
the
line
willbe
reflected
and
appear
in
the
output.
Since
resistors
are
not
available,
in
a
suitable
power
rating,
which
ap-
pear
resistive
over
the
wide
passband
of
the
Type
541,
an
adjustable
terminating
network
is
used,
The
coils,
L1070
and
L1071,
are
wound
with
resistance
wire
and
have
a
total
resistance
of
595
ohms.
Each
section
has
a
characteristic
impedance
which
is
approximately
equal
to
the
impedance
of
the
plate
lines
less
the
series
de

resistance between it and the plate lines.
VERTICAL AMPLIFIER CIRCUIT DETAILS
Type 541, S/N 6475 and up
In Type 541 instruments, Serial Numbers
6475 and up, the signal input from the plug-in
unit is coupled through terminals 1 and 3 of the
interconnecting plug to the grids of the Input
Amplifier stage. R1027 varies the cathode
degeneration, and thus sets the gain of the stage
to agree with the Preamplifiers front-panel
calibration when the VARIABLE knob is in the
CALIBRATED position.
The Input Amplifier is coupled to the Distri-
buted Amplifier by the cathode followers V1033
and V1043. The cathode followers isolate the
Distributed Amplifier from the Input Amplifier,
and provide the necessary low-impedance drive
for the Distributed Amplifier's grid lines.
High-frequency compensation for the Input
Amplifier is provided by the variable peaking
coils L1014 andL1024. Variable inductors L1036
and 11046 provide additional peaking at the
very high frequencies.
Output Stage
The output stage is a 6-section Distributed
Amplifier. The tapped inductors in the trans-
mission line, between each grid and between
each plate, isolate each section from the capaci -
tance of the adjacent sections,
The input signal for eachtube is obtained from
the grid line, which is driven by the cathode
followers V1033 and V1043. The amplified signal
at each plate, fed to the plate line, becomes
an integral part of the wave traveling down the
line toward the deflection plates.
The vertical signal is delayed Q.2 microsecond
between the input to the grid line and the verti-
cal deflection plates. This delay insures that
the very "front" of fast vertical signals can be
observed. About 0.015 microsecond of the total
delay time occurs in the Distributed Amplifier;
the remaining 0,185 microsecond occurs in the
Delay Line.
The tapped inductors between each section of
the Distributed Amplifier provide about 0.003
microsecond of delay. By making the delay time
in the grid and plate lines equal, the signal
PAGE 3-6
arriving at each plate, through the electron
stream of the tube, will be synchronous withthe
signal ‘moving down the plate line from the
preceding sections.
DC Shift Compensation
DC shift in the amplifier --a condition whereby
the de and very low-frequency transconductance
is less than at mid-frequencies -- is compensated
for in two ways. R1090 and Ci093B, in plate
line L1104, and R1095 and C1093D in plate line
L1114, form a low-frequency boost network; the
time constant of this network is such that the
termination resistance of the line is increased
in the range from very low frequencies to dc.
A longer time constant, for extremely low-fre-
quency and de compensation, is provided by
R1092, R1094 and C1093A, in one plate line, and
by R1097,, R1099 and C1093C in the other, which
provide a small amount of positive feedback from
the plate lines to the plate circuits of the Input
Amplifier. A variable resistor R1091, the DC
SHIFT COMP. control, is connected between the
two networks to adjust for the proper amount of
compensation.
Beam-Position Indicators
The beam-position indicators, B1083 and
B1087, located on the front panel above the crt,
indicate the relative vertical position of the
trace with respect to the center of the graticule.
When the beam is centered vertically, the po-
tential across either neon is insufficient to
light it. As the beam is positioned up or down
the screen, however, the current through the
Indicator Amplifiers, and hence the voltage
across the neons, will change. The voltage
across one neon will increase, causing it to
light, and the voltage across the other will de-
creasc, causing it to remain extinguished. The
neon that lights will indicate the direction in
which the beam has been moved.
Trigger Pickoff
When internal triggering of the Time Base
Generator is desired (black TRIGGER SLOPE
knob in either the +or-INT. position), a "sam-
ple" of the vertical signal is used to develop the
triggering pulse. This "sample" is obtained
from the trigger pickoff circuit consisting of the
Trigger Pickoff Amplifier V1054 and V1064,
and Trigger Pickoff C.F. V1223B
oe
531/541-CIRCUIT DESCRIPTION

This "sampie" of the vertical signal is also
ac-coupled, through V1223A and C1228, to a
front-panel jack labeled VERT. SIG, OUT.
Delay Line
The output signal from the Vertical Amplifier
is coupled through the balanced Delay Line to
the vertical deflection plates of the crt. The
function
of
the
Delay
Line
is
to
retard
the
arrival of the waveform at the deflection plates
until
the
crt
has
been
unblanked
and
the
hori-
zontal
sweep
started.
This
delay,
as
mentioned
previously, insures that the very " front" of fast
vertical
signals
can
be
observed.
The
line
is
adjusted, by means of the variable capacitors
connected
across
the
line,
for
optimum
transient
response.
The entire Delay Line, which includes the
plate’ line in the Distributed Amplifier, is re-
verse-terminated
in
its
characteristic
impe-
dance,
The
Termination
Network,
shown
on
the
Vertical
Amplifier
diagram,
is
designed
to
dis-
sipate
both
the
dc
and
signal
energy
in
the
line
by presenting a constant resistance over the fre-
quency
range
of
the
amplifier.
The
terminating
resistors R1O71 and R1073 are specially made,
wirewound, noninductive, distributed resistors.
The 600 ohms total resistance in each is
"tapered" | or distributed, in steps. The largest
segment
of
the
terminating
resistance
appears
nearest
the
line;
the
smallest
segment
appears
at the opposite end. Each step of the resistance
is then tuned, by means of the variable capaci-
tors, so that the network will present an opti-
mum. load to the line.
CALIBRATOR
The calibrator is asymmetrical multivibrator
with V670A and V670B connected so it will turn
cathode follower V246A on and off as it oscil-
lates. During the negative pulse at multivibrator
V670A, the grid of the cathode follower is driven
well below cutoff, so the cathode is at ground
voltage. During the positive pulse at the multi-
vibrator the plate is cutoff and rests slightly be-
low +100 volts, The voitage of the plate during
cutoff is determined by the setting of R679, part
of a divider between +100 volts and ground.
R679 is a screwdriver adjustment labeled CAL
ADJ. Cathodes of the multivibrator are returned
to -150 volts. The multivibrator frequency is
about one kilocycle.
Cathode follower V246A has a tapped cali-
brated voltage divider for its cathode resistor.
When the CAL ADJ, control is properly set, the
cathode follower cathode is at + 100 volts when
V670A is cut off. Taps on the divider divide the
100 volts down to 50, 20,10,5, 2,1, .5, and .2
volts. A second divider with a division ratio of
1000 to 1, can be switched inif desired to divide
these voltages into millivolts. C682 from the
cathode-to-ground corrects a slight overshoot.
No internal connection from the calibrator to
the vertical-deflection circuits is provided.
HORIZONTAL-DEFLECTION
SYSTEM
SWEEP
CIRCUITS
Trigger Amplifier
The
TRIGGER
SLOPE
switch
selects
the
source
of
triggering
voltage
and
arranges
the
trigger-amplifier
input
circuit
to
produce
nega-
tive-going
output
for
either
negative-going
or
positive-going
portions
of
the
input
signal.
The trigger amplifier, V8, is agrounded-grid
cathode-coupled
linear
amplifier.
A
capacitor,
C3,
can
be
switched
into
the
grid
circuit
to
remove
the
dc
component
of
the
trigger
signal.
Output
is
always
taken
from
the
A-section
plate,
but the
TRIGGER
SLOPE
selector
connects
either
the
A-section
grid
or
the
B-section
grid
to
the
input
signal
source.
For
positive-going
signals
connection
is
made
tothe
A-section
grid,
and
for
negative-going
signals
connection
is
s
531/541—-Cl RCUIT DESCRIPTION
made to the B-section grid, and in each case
the
opposite
grid
is
connected
to
an
adjustable
dc
bias
source,
adjustable
by
means
of
the
TRIGGERING
LEVEL
control.
R14
adjusts
the
bias
on
one
half
or
the
other
of
V8
to
adjust
the
de
level
of
the
A-section
plate
output.
The
dc
level
of
the
plate
output
is
important
to
the
circuit
operation
in
three
of
the
five
positions
of
the
TRIGGERING
MODE
switch
because
in
these
three
switch
positions
the
input
grid
to
the
trigger
shaper
stage,
V20A,
is
dc-coupled
to
the
plates
of
V8.
The
effect
of
the
dc
level
is
shown
ina
later
paragraph.
Triggering Mode Switch
The
TRIGGERING
MODE
switch,5W5,
has
five
positions
marked
in
red
in
the
upper
right-hand
PAGE 3-7