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24 Circuit description
give rise to a shift of the light spot on the screen. This is avoided by
equalizing the values of the d.c. voltages on the anodes of Bl' and B2'
by means of potentiometer R57 (DC-Balance), so that no d.c. voltage
arises across R6.
Resistor R37 in the control grid circuit of valve Bl serves to limit the grid
current in the case of positive input signals. The adverse influence of this
resistor on the square wave response is eliminated by parallel capacitor
C34.
3. Output stage
Output amplifier B3-B3' is preceded by the cathode followers Bl' and
B2', which are provided to reduce the influence of the high input capa-
citance of the output valves on the anode impedance of the valves Bl and
B2. As a result the bandwidth of the amplifier is larger than if the valves
Bl and B3 or B2 and B3' were directly coupled to the preceding stage. The
shift controls R4-R4' are included in the control grid circuit of the
cathode followers. By means of these potentiometers the d.c. voltage on
the control grids of Bl' and B2' can be varied. The variation on the grid
of B l ' opposite to that on the grid of B2'. As a result the image will
shift in the vertical direction across the screen. The shift voltage is applied
to the control grids of Bl' and B2' via the voltage dividers with high
impedance R76-R64 and R72-R70 respectively. By means of these
voltage dividers the anode potentials of valves Bl and B2 are made in-
dependent of the position of the shift controls (R4, R4'), so that the d.c.
balance is maintained. Capacitors C36 and C37 prevent the voltage
dividers from affecting the square wave response. By means of potentio-
meter R80 the feedback of both output valves is adjusted in such a way
that the maximum Y sensitivity is 10 mV
p
-
p
/div.
The symmetry of the signal in the output stage is increased due to the
common cathode resistor. The anodes of B3 and B3' are directly con-
nected to the Y deflection plates. For driving the time base generator in
the case of internal triggering use is made of that part of the anode volt-
age of B3, which is applied to the first valve (B501) of the trigger pulse
shaper via switch SK5.
B. TRIGGER PULSE SHAPER (unit D, Fig. 31)
The trigger pulse shaper consists of an amplifier stage (B501) and a
Schmitt trigger (B502-B502').
The trigger signal, which may originate from the Y amplifier (R85) as
well as from an external voltage source, is applied to the control grid of
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