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23
SERVICE DATA
Circuit diagram
I
A. Y AMPLIFIER (unit A, Fig. 29)
The amplifier for the Y deflection is a d.c. coupled push-pull amplifier.
The voltage under test is connected to socket BU2 (DC) or to socket BU3
(AC) and subsequently applied to the output amplifier via an attenuator
circuit and a phase inverter.
1. Attenuator circuit
An attenuator circuit, which is operated by means of SK3, is included in
the input circuit of the Y amplifier.
In the positions "3 V/div." and "10 V/div." of SK3, thesignal to be measur-
ed is attenuated by the voltage dividers R34-R26//R41 and R35-R27//R41
A step attenuator with high impedance (R36-R28 ... R32) is included
in the other positions of SK3. The attenuator switch has eight calibrated
positions. By means of the trimmers C27, C28 and C29 and the capacitors
C30, C31, C32 and C33, the attenuators are adjusted in such a way that
in all positions of SK3 the attenuation is frequency independent.
2. Phase inverter stage
Via the attenuator circuit the signal to be measured is applied to the
phase inverter stage with the valves Bl and B2. This stage is driven on the
control grid of valve Bl. Valves Bl and B2 are coupled via the common
cathode resistor R40. As the control grid of B2 is connected to earth via
R42, this valve is driven by a voltage whose magnitude is equal to the
signal to be measured, but opposed in phase to the latter. The voltage on
the anodes of Bl and B2 are symmetrical with respect to the average d.c.
voltage difference between these anodes.
The amplitude of the signal can be adjusted continuously by varying the
value of the anode resistors R43 and R49 - and thus the amplification -
by means of potentiometer R6.
Turning potentiometer R6 would also result in a variation of the average
d.c. voltage on the input of the next amplifier stage (B1 '-B2'), which would
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