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73
3. 1.6.4.
Blanking
circuit
The
blanking
circuit
blanks the
c.r.t.
during the
fly-back of the
time-base
and unblanks
the
c.r.t.
during the
sweep and
constantly
If
TIME/cm
switch
SK2
occupies
position
X
via Y/\.
The
blanking
circuit
operates
on
a
low
voltage
level
and comprises an
a.c.
and
a
d.c.
path.
Transistor
TS706
is
driven
by
the collector
signal
of transistor
TS504
in
the sweep-gating multivibrator.
Transistor
TS706
forms
together with
transistor
TS704
a
single-ended push-pull
circuit.
—
A.C.
Path:
The
amplified
a.c.
components
of the blanking
signal are
fed
direct to
the
Wehnelt
cylinder
of
the
c.
r.t.
via
H.T. capacitor
C707.
—
D.C. Path:
For
the
d.c.
component
of the
blanking
signal,
the
signal
of
oscillator
TS702
&
TS703
is
used.
The
oscillator signal
Is
modulated
with
the blanking
signal.
The
amplified
modulated
signal
on
the
collector
of
transistor
TS703
is
via
capacitor
C706
fed to
demodulator
GR702-R713.
After
demodulation,
also the
d.
c.
component
of the
blanking
signal
is
available.
The
a.c.
and
d.c.
amplifications
are
equalized
by means
of
potentiometer
R71
1.
3.1.7.
CALIBRATION
VOLTAGE
The
calibration voltage
generator
consists of
free-running multivibrator
TS750
&
TS751.
The
generator frequency
is
approximately 2 kHz.
The
amplitude
of the
generated square-wave
voltage
is
kept
at
a
constant
value
by
means
of zener
diode
GR751. The
exact value
of the calibration voltage
is
set
with the
aid
of
potentiometer
R761.
3.1.8.
POWER
SUPPLY
The power
supply comprises
the
mains
transformer,
stabilized
supply and
converter,
and
the
circuit for
the
graticule illumination.
EXT. DC.
SUPP.
Fig.
3.8.
Power
supply
3.1.
8.1.
Mains transformer
Mains transformer
TS801
has
three
primary windings which,
together
with one secondary winding, can be
combined by means
of voltage
adapter
SK21.
This
combination
allows the
instrument
to
be used with
mains
voltages of
1
1
0
V,
1
27
V,
220
V
and
240
V.
The
voltage
on secondary winding S3
is
full-wave
rectified.
The
resulting
negative
d.c.
voltage,
or
alternatively^
a
negative
d.c.
voltage
on
EXT DC SUPPLY
input socket
BUS,
is
applied to the voltage
stabilizer
and conveter.
Part of
the
a.c.
voltage
on winding
S3
of the
mains
transformer
is
fed to
MAINS
trigger
source switch
SK7,
to enable
internal triggering
on
the
mains
frequency.
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