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69
Moreover,
this
transistor
improves
the
stability
of the pre-amplifier.
The
external
trigger
input
Is
protected
against excessive positive
input
voltages
by means
of
diodes
GR401
and
GR402.
3.1.
3.3.
Long-tailed
pair circuit
(differential
amplifier)
The
following description
applies to internal
triggering.
From
the pre-amplifier the
triggering signal
is
fed to the long-
tailed
pair circuit
with
transistors
TS403
and
TS404.
The
signal
is
applied to the base
of transistor
TS403
if
+
push-button
SK8
Is
depressed
and
to
the base
of
TS404
if
—
push-button
SK9
is
depressed.
This allows
triggering
on
either
the
positive
or negative slope of the
signal.
The
+ push-button
SK8
is
a
mechanical
release
for
—
button
SK9
and
is,
therefore,
not included
in
the
circuit
diagram.
A
d.c.
voltage
which
is
variable
with
LEVEL
potentiometer R3'
is
applied to the base of the
non-driven
transistor
of the
long- tailed pair
circuit.
As
a
long- tailed pair circuit
amplifies the difference of the base voltages, the setting of
potentiometer R3'
determines
which
part of the
signal
will
be amplified
and,
thus,
the
trigger
level.
The
output
signal
of the
long-tailed pair circuit
is
fed to
emitter follower
TS406.
If
AUTO
push-button
SK10
is
depressed, the
a.c.
component
of the emitter
signal
of
TS406
is
applied to the full-wave
rectifier
with diodes
GR404
and
GR406. The
rectified
voltage across
LEVEL
potentiometer
R3"
corresponds
to the
peak-to-peak
value of the
a.c.
component
of the
triggering
signal.
This
d.c.
voltage
is
fed to the base of transistor
TS404
of
the
long- tailed pair
circuit.
The
result
is
that
in
the
auto
mode
the
trigger
level
range
corresponds
to the peak-
to-peak value of the
triggering
signal.
3. 1.3.4.
Synchronisation separator
If
T.V. push-button
SKI
3
is
depressed,
a
synchronisation separator
for
television
is
inserted into
the
triggering
signal
path.
The
sync
separator
comprises
transistor
TS407. The
television
signal
is
clipped
in
such
a
way
that
only
the
synchronising
pulses reach the collector of transistor
TS407.
In
positions
.2
jus
to
20
jus
(TV
LINE)
of
TIM
E/cm
switch
SK2,
these pulses are supplied direct to emitter follower
TS408.
In
positions
50
jus
to
.5
s
(TV
FRAME)
the
composite
synchronising
signal
is
Integrated
by
means
of
R439,
C412,
GR407, R442
and
C413
at
such
a
timexonstant
that the
frame
pulses are separated.
The
separated
pulses
are
applied to emitter following
TS408.
3.1.3.5. Trigger-pulse
shaper
The
trigger-pulse
shaper comprises
transistors
TS501
&
TS502
in
Schmitt-trigger configuration.
With
a
repetitive trigger
signal, a
square-wave
voltage of
constant amplitude
and width
arises at
the collector of
TS502.
This square-wave voltage
is
differentiated
by
C502
and
R514
into
narrow
positive
and
negative pulses.
The
positive pulses are short-circuited
by
GR501
so that sweep-gating multivibrator
TS503-TS504
receives
only
negative
pulses.
3.1.4.
TIME-BASE
GENERATOR
The
time-base generator
comprises
a
sweep-gating
multivibrator,
a
sawtooth
generator,
a
hold-off
circuit and
an auto
circuit.
X
FINAL
"amplifier
Fio.
3.4.
Timfhhase aenerator
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