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13
the
negative
feed -back in such
away
that
if
the output
voltage
increases
the negative
feed-back also
increases,
so
that the
output
voltage remains
eons
tant.
The
level of the oscillator
voltage
can
be
adjusted with
R26. Thermistor R9
stabilises
the bias
conditions
!il
TS2 up to a temperature of
approximately
40°C.
D. THE OUTPUT VOLTAGE
The output circuit is
indicated
in the block diagram
(Fig. 2)
by
the letter C. The
output voltage
can
optionally
be
either
sinusoidal
or
square.
The
sinusoidal voltage can
be
taken
from the Wien bridge
while
the
square
wave
voltage
is disch arged from the
sinusoidal voltage
by limiter
circuit
TS6
/
TS1. These transistors
are alternately
cut
off
and
saturated.
The
output volta ge
of stage
TSl can be kept
more
constant with
the aid
of
Zener diod
e
GRZ1. The
square wave
voltage consists
of negative-going
pulses. But the
d.c.
voltage level
can be
changed
by
a
circuit
for adjusting
the d.c.
voltage
level (see
Chapter III, C2).
The
mark/
space
ratio can be adjusted with trimming potentiometer
R20
(Fig. 4).
The
output
potentiometer
(R2)
enables
continuous amplitude va
riation
of both the
sinusoidal and
the
square wave volta ge.
E. SUPPLY
The
apparatus is supplied
by two
9-V
batteries connected
in series.
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