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external negative pulse is applied through R113, C104, and CRIOI to the gate of
Q102, causing the firing level of the unijunction to decrease.
The sawtooth voltage at the anode of Q102 is directly coupled to the base of
Q103.
Q103 is a driver amplifier and has two transistors wired as a darlington
pair; their input and output leads exit as a three-terminal device. This device
exhibits a high input impedance to Q102, and thereby maintains excellent impedance
isolation between Q102 and Q104.
The output waveform from the unijunction oscillator is not suitable, as yet,
to produce a satisfactory vertical sweep. Such a waveform would produce
severe stretching at the top of the picture and compression at the bottom. C105
and C106 modify the output waveform to produce satisfactory linearity. The
sawtooth waveform output at Q103 is coupled through R122, the vertical linearity
control R121, and on to C106 where the waveform is shaped into a parabola.
This parabolic waveform is then added to the oscillator' s waveform and
changes its slope.
Slope change rate is determined by the position of the variable
resistor R121.
Q103 supplies base current through R123 and R124 to the vertical output
transistor, Q104. Height control R124 varies the amplitude of the sawtooth voltage
present at tlie base of Q104 and, therefore, varies the size cf the vertical raster
on the CRT.
The vertical output stage, Q104, uses a power type transistor which operates as
a class A amplifier. No output transformer is required since the output impedance
of the transistor permits a proper impedance match with the yoke connected
directly to the collector. C107 is a DC-blocking capacitor which allows only
AC voltages to produce yoke current. LI is a relative high impedance compared
to the yoke inductance. During retrace time, a large positive pulse is developed
by LI whcih reverses the current through the yoke and moves the beam from the
bottom of the screen to the top. Resistor R126 prevents oscillations by proridirig
damping across the vertical deflection coils.
A-3
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