418 Highvoltage Power Supply

4-19. Figure 4-3 is a block diagram of the high voltage power supply. The output of a regulated transistor oscillator is stepped up in voltage and applied to a series of high-voltage rectifiers. The positive output of the voltage doubler is connected to the post-accelerator of the CRT. The negative output voltages are used in the gun assembly of the CRT and its associated controls. The Z-AXIS INPUT can be used to apply an intensity modulating signal to the cathode of the CRT.

4-20. Figure 5-8 is a schematic diagram of the highvoltage power supply, including the CRT. Oscillator Q302 operates at a frequency of about 32 kc. Any change in the output voltage is applied to the grid of V301, which converts the voltage change to a current change. This current change is applied by emitter follower Q301 to the base of the oscillator transistor. The amplitude of oscillations is changed in such direction as to oppose the original output voltage change. High Voltage Adjust R319 sets the amplitude of oscillation to produce the correct output voltage.

4-22. Two separate negative supplies are used, one for the control grid of the CRT, and one to provide CRT cathode and focusing voltages. Both supplies use half-wave rectifiers (V304 and V305). The un-blanking gate from the horizontal plug-ins (via pin 1, J2) is applied to the return side of the grid supply, and changes the negative grid voltage by about +50 volts to unblank the trace. A positive pulse of about 20 volts will blank the trace when applied to Z-AXIS INPUT. When Z-AXIS INPUT is not used, S301 is set to INT to receive chopped blanking from a dual-trace plug-in.

4-22. The voltage doubler circuit (V302/V303) provides the 5-kc post-accelerating voltage required by the CRT.

4-23. The ASTIGMATISM adjustment (R341) affects the roundness of the spot, and the Geometry adjustment (R343) is used to optimize pattern shape.

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