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Circuit description
E. CATHODE RAY TUBE CIRCUIT (unit B, Fig. 35)
1. Intensity and brightness control
%
The brightness of the picture can be changed by varying the potential on
the Wehnelt cyclinder by means of RI.
A pulse-shaped voltage, which is applied to the Wehnelt cylinder via
capacitor C519, is taken from the anode of B503. This pulse-shaped
voltage is high during the forward sweep of the sawtooth voltage and low
during the flyback. As a result the electron beam is suppressed during the
flyback of the sawtooth voltage, because the positive peak of the pulse-
shaped voltage is retained by diode GR30I almost on the level adjusted
with Rl. Capacitor C30I serves to prevent crosstalk of the brightness
pulse on the negative supply voltage and to smooth the ripple of the
negative supply part.
2. Focusing and astigmatism
The line on the screen can be adjusted sharply by means of potentiometer
R2. This potentiometer regulates the voltage on the focusing anode g3
of valve B301. Astigmatism of the electrostatic lens can be corrected by
adjusting the voltage on the last acceleration anode (g4) to the correct
value by means of potentiometer R305.
3. Barrel and pincushion distortion
This is due to faults (for instance fringe areas) in the electrostatic lens and
can be corrected by adjusting the voltage at the beginning of the post-
accelerating coil to a certain value by means of potentiometer R309.
F. SUPPLY PART (unit E, F, Fig. 38)
The supply part delivers voltages of +280 V, +160 V, —150 V and
+ 1610 V.
The voltage of +280 V is electronically regulated and stabilised.
1. +280 V
The Graetz circuit GR 1001 . . . GR 1004 supplies a full-wave rectified
voltage, which is applied to the control circuit.
This control circuit consists of a series regulator (B 1001), control valve
(B1001') and a stabiliser (B1002), The latter keeps the cathode of B100I'
at a constant potential of 85 V. A load variation or mains voltage varia-
tion in the +280-V supply circuit will result in a change of the +280-V
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