Volts Div Var Circuit and X1X10 Amplifier

The appropriate voltage divider signal output (-M, +2.5, or -i-5) is selected by VOLTS/DIV switch S105B and routed to the Volts/Div Var circuit composed of C141, R141, and R143.. Changes that occur in the Buffer Amplifier output impedance due to setting R141 or switching the divider output are sensed via R139M. These changes modify the slow-path feedback signal to cause U120 to again match the gain of both paths.

From the Volts/Div Var circuit, the signal is applied to the input of the X1/X10 Switchable-gain Amplifier U145. Amplifier U145 produces a differential output signal from the single-ended input signal. The gain of the amplifier is controlled by the setting of VOLTS/DIV switch S105.

Amplifier gain is changed by switching between two pairs of transistor amplifiers contained in U145. Gain of the X10 amplifier pair is adjusted by R145 to obtain the

Transistors U170D and U170E form a common-emitter amplifier. The gain of U170D and U170E is set by R180 (connected between the emitters), and the high-frequency response is compensated by C180. The emitters are also connected to the bases of U170C and U170B respectively to provide an internal trigger signal pickoff point. Vertical signal output current flows from the collectors of U170D and U170E to the emitters of common-base amplifiers Q177 and Q187. A shunt resistor gain network (R176 and R186) sets the gain of the common-base stage. Channel 1 POSITION control R190 supplies a variable offset current to the emitters of Q177 and 0187 which allows the trace to be vertically positioned on the crt. The common-base amplifier stage converts the differential signal input current to a differential signal output voltage that is applied to the Diode Gate circuitry (Diagram 3).

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