The pre-distorted signal is applied to the input transistor
of a differential amplifier comprised of Q702, Q703 and
constant current source Q704. The current supplied by
0704 is split almost equally between Q702 and Q703
resulting in similar no signal collector voltages within
5% of the supply level. Very heavy negative feedback is
applied to the base of Q703 from across R720, a non-
inductive current sensing resistor. The voltage across
which supplies an accurate representation of yoke cur-
rent and forces the amplifier to correct any distortion pre-
The signal present at the collector of Q702 is current
amplified by 0705 and this in turn is used to drive Q706
which then drives the output transistors Q708 and Q709
forcing current through the x-winding of the yoke and pro-
ducing beam deflection.
The output transistors are current driven with the actual
driver transistor being Q706 and its constant current
source being Q707. D708 is used to hold the bases of
Q708 and Q709 separate by 0.6 of a volt. This results in
output transistors that are biased class B. Because of
push pull arrangement of output transistors, and the
cancelling effect of such a stage on any common ripple
component considerable amount of power supply rippie
can be tolerated. Any small amount of crossover distor-
tion that may result from class B operation is removed by
means of the very heavy negative feedback present. C704
is used to maintain a low impedance path across D708.
Q704 is a constant current source with fixed bias voltage
maintained by D706 and D707 with R711 allowing current
to flow through them from -ve rail to ground.
Q707 works exactly the same way as Q704 except R716
has been added to dissipate more power where total cur-
rent flowing through both Q707 and R716 is constant.
R712 is a suppressing resistor to prevent spontaneous
oscillation of Q707. C701 is an H.F. bypass.
R721 is a resistor critically selected to damp the yoke
and minimize any tendency for ringing.
In case of a failure of an output device or an extreme ex-
cursion of the electron beam, F700 will open and prevent
damage to the yoke or sense resistor as well as remove
all loading from Q708 and Q709, thus protecting those
from potential failure also.