Section
5
Calibration
Introduction
The
Type
561A
Oscilloscope
should
be
calibrated
af’
er
each
500
hours
of
operation,
or
every six
months,
whichever
occurs
first.
In
addition,
the
calibration
should
be
checked
and
adjusted
as necessary
after
replacement
of
any
port.
Normally,
the
instrument
will be
calibrated with
be
th
plug-in units
inserted.
When
performing
a
complete
cali
bration, you
should
calibrate
the
indicator
unit
first,
then
the
amplifier
unit
or units,
and
then
the
time-base
unit,
if
one
is
used. Either
or
both
of
the
plug-in
units
can
be
calibrated
separately
although
the
power-supply
voltages
in
the
indicator
unit
should
always
be
checked
before
calibrat
ing
any
part
of
the
instrument.
The
following
equipment
is
required
for
a
complete
cali
bration
of
the
Type
561
A
Oscilloscope:
1.
De
voltmeter
(sensitivity
of
at
least
5000
ohms
per
volt),
calibrated
for
an
accuracy
of
±1%
from
0
to
300
volts,
and
for
an
accuracy
of
zh3% at
4000 volts.
2. Variable
autotransformer with
a
rating
of
at
least
250
watts.
3.
Accurate
rms-reading
ac
voltmeter
with
a
range
of
at
least
0
to
125
volts
(0
to 250
volts
for
234-volt
instru
ments).
4. Test
oscilloscope
with
calibrated vertical
sensitivity
of
50
millivolts
per
division
or
better.
5.
Capacitance
meter
capable
of
a
measurement
accuracy
of
0.1
picofarad
or
better
at
16
picofarads; meter
must
have
guard
voltage
available. Tektronix
Type
130
L-C
Meier
recommended.
To
set
up
the
Type
561
A for
calibration,
insert
t
vo
plug-in
units
known
to
be in
proper operating
condition.
If
one
is
a
time-base
plug-in
unit,
adjust
its
controls
so
no
sweep
is
produced.
Connect
the
autotransformer
to
a
suit
able power
source
and
connect
the
Type
561
A Oscillosccpe
to
the
output
of the autotransformer.
Turn
on the
equipment
and set
the
output
of
the
autotransformer
for
the
nominal
operating
voltage
of
the
oscilloscope
(117
volts
or
734
volts).
Allow
the
equipment
to
warm
up
for
about
10
minutes.
Power
Supply
With
the
de
voltmeter, measure
the
output
of
the
—12
2-,
-1
00-,
+125-,
and
+300-volt
supplies
at
pins
16,
23,
15,
and
10, respectively, of
the
plug-in
connectors.
Set
he
— 100
V
adjustment
to
exactly
—
100
volts.
All other
sup
plies
should then
be
within
3% of their
rated
values.
Measure
the
voltage
at
the
HV
TEST
POINT
(Fig.
4-2)
on
the
ceramic
terminal
strip
below the
high-voltage
shir
Id.
Adjust
the
HIGH
VOLTAGE adjustment
for
a
reading
of
—
3300
volts.
Using
the
test
oscilloscope,
measure
the
amount
of
ripple
at
the
output
of
each
supply.
The
ripple
will
be
twice
the
line
frequency.
With
plug-in
units
inserted,
he
nominal
ripple
is
5
millivolts
on
the
—
100-volt
supply,
10
millivolts
on
the
+
125-volt
supply, 80
millivolts
on
the
+
300-volt
supply,
and
3
millivolts
on
the
—
12.2-volt
supply.
Do
not
attempt
to measure
ripple
on the
-3300-volt
supply.
Vary
the
autotransformer
output
voltage
between
105
and
125
volts
(or
210
and
250
volts
if
the
power
transformer
is
wired
for
234-volt
operation)
and
check
to
see that
all
voltages
stay
within
tolerance
over
this
range.
Calibrator
Set the CALIBRATOR
switch
to
OFF
and
set
the
CAL.
AMPL.
adjustment
so
the
voltage
at the
cathode
of
V884B
(pin
7)
is
exactly
+100
volts.
Calibration of
the
various
settings
of
the
CALIBRATOR
switch is
not
necessary.
Crt
Circuit
Check
to
see
that
only
the
face
plate
of
the
crt
extends
beyond
the
front
panel
of
the
instrument. If
it does
not,
loosen
the
crt
clamp
screw
and
move
the tube
forward
by
pushing
on
the
tube
socket.
Then
retighten
the
crt
clamp
screw.
If
you
are using
a
time-base
unit,
set
it
for
a
free-running
sweep.
If
you
are
not
using
a
time-base
unit,
apply a
signal
to
the
right-hand
unit
to
produce
a
horizontal
trace
at
least
10
centimeters long.
Set
the
FOCUS
and ASTIGMATISM
controls
for
the
narrowest
trace
width
and
position the
trace directly
behind
one
of
the
graticule
lines.
Adjust
the
crt
ALIGNMENT
control as
necessary
to
align
the
trace
with
the
graticule line.
Crt
Geometry
The
GEOMETRY
adjustment
is
set
to
achieve
minimum
curvature
of
vertical
lines
displayed
at
the
edge
of
the
graticule.
Insert
a
time-base
unit
into
the
right-hand
opening
and
a
vertical
amplifier unit
into
the
left-hand
opening
of
the
Type
561A.
Connect
the
output
of
the
Calibrator
to
the
vertical
amplifier
and
adjust
the
time-base
unit
to
display
two
to
five
cycles
of
the
Calibrator
signal.
Adjust
the
amplitude
and
position
of
the
display
so
the tops
and
bottoms
of
the
pulses
are
just
visible
at
the
top
and
bottom
of
the
crt.
Then
set
the
GEOMETRY
adjustment
to
eliminate any
curva
ture
of
the
vertical
lines
located
near
the
edge
of
the
graticule.
Effective
Deflection-Plate
Capacitance
The
effective
deflection-plate
capacitance of
the
crt
as
seen
by
the
plug-in units
can
be
adjusted
by
means
of
C760
and
C761
.
This
capacitance
has
been
set
at
the
factory
to
provide
a
standard
effective
deflection-plate
capacitance
of
16
pf.
If
C760
or
C761 has
been
inadvertently
misadjusted,
or
if
the
crt has
been
changed, the effective
capacity
between
one
or
both
pairs
of plates may
be
altered
slightly.
5-1
