Table of Contents
Advertisement
28 Circuit description
a constant current supplied by capacitor C5I8, as a result of which the
voltage across this capacitor increases linearly (this is the forward sweep
of the sawtooth voltage). As soon as the amplitude of the sawtooth
voltage has reached a given value, valve B503 becomes conductive.
As a result the Schmitt trigger B503-B503' switches over to the condition
B503 conductive - B503' cut-off. The voltage on the control grid of B503
then drops to the cathode voltage of valve B503. The resultant grid
current of valve B503 causes the control grid voltage of valve B501' to
drop likewise. This voltage drop is applied to the cathode of diode GR503
via valve B501' connected as a cathode follower and capacitor C518.
This diode becomes again conductive and the potential of the junction
R53I-C518 is again determined exclusively by the potential of the anode
of valve B501'. In this period the time base capacitor discharges across
R530, across the diode formed by the control grid and the cathode of
valve B503 and across resistor R52I until the voltage across the capacitor
is equal to the cathode voltage of B503 (this is the flyback of the sawtooth
voltage). At the end of the flyback C518 is charged again via diode
GR503 and the low output impedance of cathode follower B501'. This
condition, the waiting period, is maintained until multivibrator B503-
B503' is again changed over by a trigger pulse.
3. Linearity of the sawtooth voltage
The sawtooth voltage has a good linearity due to the good transmission
of the cathode follower, the large capacitance of capacitor C518 and the
use of diode GR503.
4. Sweep time
The slope of the sawtooth voltage- and thus the sweep time per division-
depends upon both the value of the time base capacitor and the charging
current. The sweep time can thus be varied by changing the value of the
time base capacitor. The time base capacitors are selected with SK2, by
means of which twelve sweep times can be adjusted. By means of R533
the charging current is adjusted in such a way that the sweep times per
unit of length comply with the orientation values on the text plate to
within 25%.
5. Sawtooth voltage
The sawtooth voltage is available across resistor R733 (Fig. 33). The
amplitude of the voltage applied to the X amplifier is determined by the
value of R733.
Advertisement
Table of Contents
