Horizontal Output Amplifier

The Horizontal Output Amplifier converts the single-ended output of the Preamplifier into the differential output required to drive the crt horizontal deflection prates. The output stage consists of an input paraphase amplifier and an output complementary amplifier.

Horizontal signal voltage from Q736 is applied to the base of Q763. The base of the other transistor (Q753) in the paraphase amplifier, is biased through a voltage divider composed of R758, R757, and R756. Horizontal centering between the X1 and X10 Magnified sweeps is accomplished by adjusting Mag Registration potentiometer R758.

Gain of the paraphase amplifier is determined by components connected between the emitter leads of Q763 and Q753. The exact gain is adjusted by Horiz Gain potentiometer R752.

Transistor Q747 supplies the emitter current to both Q763 and Q753. The horizontal portion of the Beam Find circuitry affects the available current to Q747. Normally, -8.6 V is applied to the emitter of Q747 from the BEAM FIND switch via CR745 and R746. When the BEAM FIND push button is pressed in, the direct -8.6 V is removed. In this condition, -8.6 V is supplied via R745 which reduces the current available, thereby reducing the output voltage swing capability of Q763 and Q753. Diodes CR772, CR782, CR783, and CR773 prevent the paraphase amplifier from overdriving the output amplifier stage when the X10 Magnification feature is in use.

Final amplification of the horizontal deflection signal is provided by the complementary-pair output stage. Both sides of the differential output amplifier are identical in function, so only one side is discussed in detail.

Transistors Q780 and Q785 form a cascode feedback amplifier. Gain of the stage is set by feedback resistor R785, and high-speed compensation is provided by C783 and adjustable capacitor C784. For dc and low-frequency components of the horizontal deflection signal, Q789 acts as a current source for Q785. High-frequency components of the signal are coupled through C789 to the emitter of Q789 to speed up the output response time.

Emitter voltage for both Q780 and Q770 is supplied by a circuit composed of Q765 and associated components. The emitter voltage is maintained at a level that provides proper biasing for Q763 and Q753. Diodes CR770 and CR780 set up an emitter-bias difference between Q780 and Q770, causing the base voltage of both transistors to be equal.

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