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Circuit description
29
D. X AMPLIFIER (unit C, Fig. 33)
Except for the input circuit and the anode circuit of valve B703 the X
amplifier is equal to the Y amplifier.
1. Input circuit
As desired, either an external voltage or the sawtooth voltage can be
applied to the X amplifier. In the first position of SK4 the sawtooth
voltage is taken from resistor R733 and applied to the input of the ampli-
fier. An external deflection voltage can be applied directly (via socket
BU4) or via an isolating capacitor (via socket BU5).
The position of the time base line on the screen is determined by the
potential on the control grid of valve B702. This potential can be adjusted
by means of potentiometer R746. In the other positions of SK.4 the
control grid is connected to earth via R746 and at the same time the
screen grid voltages of the valves B501 and B503 are switched off. As a
result the time base generator no longer starts, so that there is no risk of
crosstalk in the X amplifier.
The attenuator circuit, which is operated with switch SK4, is built up in
the same way as the circuit of the Y amplifier. The only difference is that
the step attenuator has only four possibilities of attenuation, so that the
deflection sensitivity of the X amplifier can be adjusted to seven values.
By means of trimmers C727, C728 and C729 and capacitors C733, C730,
C731 and C732 the attenuators are adjusted in such a way that in all
positions of SK4 the attenuation is frequency independent.
2. Amplifier stages
The amplifier stages are practically identical to those of the Y amplifier.
The difference is that the anode resistor of B703 is not divided into two
halves, as the anode resistor of B3. The anode potentials of valves B701
and B702 are equalized by means of R757 (DC-Balance), so that the
image does not shift in the horizontal direction if continuous attenuator
R7 is turned. With the double potentiometer R5-R5' the image can be
shifted horizontally across the screen. By means of R780 the sensitivity
of the amplifier is adjusted to 30 mV
p
-
p
/div.
The anodes of the valves B703 and B703' are directly coupled to the
X deflection plates.
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