Tektronix 070-8462-03, Инструкция по эксплуатации

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Theory of Operation
4–28
1735 HD High Definition Waveform Monitor
HV Osc and Error Amp. The high voltage power supply is generated by a sine
wave oscillator and step-up transformer. Q7 and T1 are the principal elements of
an Armstrong oscillator running at about 25 kHz. The error amplifier, U2,
regulates the +100 V output, and keeps the high voltage power supply constant
under varying load conditions by controlling the base current to Q7, through Q9
and Q10. The +100 V output is monitored directly, while the high voltage power
supply is monitored through a feedback circuit.
R40, C15, and R63 form the high voltage power supply positive feedback
circuit. As the current from the high voltage power supply is increased, the
voltage to the + side of the error amplifier (U2) increases, which reduces the base
drive to Q7, the high volts oscillator. This positive feedback compromises the
regulation of the 100 V supply to keep the high voltage constant with varying
intensities.
C26 and Q8 are a start delay circuit that holds the error amplifier output low,
through CR11, until C26 is charged from the 15 V supply. Delaying the start of
the high voltage oscillator allows the low voltage power supply to start,
unencumbered by the load from the high voltage oscillator
Power Supply Outputs.
CR6 is the high voltage rectifier. Smoothing capacitors
C6 and C7 work with CR6 to provide –2750 V to the CRT cathode. U1 is a
four-times multiplier, pro11 kV to the CRT anode.
Focus Amplifier.
Q2 and Q1 form an operational amplifier that sets the voltage at
the bottom of the focus divider. The front-panel FOCUS control determines the
voltage at the bottom of the focus divider. The Center Focus control, R10, is set
for optimum beam focus, as viewed on the CRT, with the front-panel FOCUS
control set to mid range. Once the Center Focus adjustment has been set,
adjusting the front-panel FOCUS control changes the voltage at the bottom end
of the divider and, consequently, the voltage on the CRT focus anode.
Grid Drive Circuit.
The grid and the cathode of the CRT are at a 2750 V potential
with the grid effectively DC coupled to the Z-axis amplifier by the Grid Drive
circuit. The unrectified, 25 kHz sine-wave output from the +100 V supply
winding is input to a modulating circuit, where it is clipped and rectified for use
as CRT control grid bias.
The sine wave from the 100 V supply winding of T1 is coupled through C16 to a
clipping circuit consisting of CR7 and CR8. Clipping level for the positive
excursion of the sine wave is set by the CRT Bias adjustment, R52; negative
clipping level is set by the front-panel intensity control through the Z-axis
amplifier. The clipped sine wave is coupled through C11 to a rectifier made up of
CR4 and CR5.