Tektronix 070-8030-01 User Manual

Theory of Operation

1780R-Series Service Manual

The Waveform Monitor high voltage supply generates all of the potentials
required to power the CRT, except for the deflection voltages. The high voltage
is derived from an Armstrong Oscillator-generated 33-kHz signal. The Error
Amplifier, which controls oscillator base current, samples the voltage on the
100-volt supply, which is also generated by the High Voltage Oscillator.

The PP Clamp provides the proper amplitude RF signal to the Grid Drive
Rectifier, which outputs a DC voltage proportional to the driving Z-axis signal.
The Focus Amplifier sets the voltage on the bottom of the focus divider. By
varying the Focus Amplifier output, the focus voltage higher up the divider
string can be varied a small amount. In line select, the CRT is driven very hard
and the Line Select Focus circuit causes the focus voltage to change during the
selected line, and then return to normal the rest of the time. Changing focus for
the selected line and then changing back keeps the readout signal, which does
not drive the CRT as hard, in focus.

The Z-Axis Amplifier provides the fast rise time signal, to the CRT control grid,
that unblanks the Vectorscope CRT.

Osc. Q221 is the active element of an Armstrong Oscillator, with C230 and the
primary of T240 resonating at 30 kHz. L110 and C120 filter the 30-kHz signal
out of the +60 volt supply.