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t6
F. FINAL
AMPLIFIER
(Fig. 25'l
The input stage of the final amplifier consists of an
asymmetrically driven long-tailed pair. The signal
enters via emitter-follower TS402 at the base of
TS404. The shift contro'l enters via TS403 at the
base of T5406.
At the emitter side of the long-tailed p'air, screw-
driver-set potentiometer Rl enables a vernier ad,just-
ment o,f the deflection coefficient. With
trimmer
C4l6 the rise-time can be adjusted to optimum. The
output stage is provided with two co'mplementary
pairs of emitter-followers.
They allow for both fast rise and fall when displaying
a squarewave, in spite of the capacitance load, pre-
sent at the input o,f the Y-amplifier and the trigger-
amplifier.
The signals enter via forward biased diodes whose
standing current can be adjusted by R449 respecti-
vely R457. If, for instance, the voltage at the col-
lector of TS404 rises, the current through GR403
decreases and the current through GR404 increases.
This gives rise to an increase of the base-current of
the NPN transistor TS407 which will become more
condictive; so the output will become more positive.
The increase of the current through GR404 causes
a decrease of the base-current of PNP transistor
TS408, which will become less conductive, offering
a higher impedance to the NPN emitter-fo,llower. As
a whole, the capacitance present at the output of the
final amplifier will be charged rapidly from a low
ohmic cuÍTent source.
At the time that the voltage at the co,llector of TS404
rises, the vo,ltage at the collector of T5406 falls. The
current through GR406 will decrease, thus opening
PNP transistors TS409.
The output capacitance will be discharged rapidly
through this low ohmic path.
The output voltage of the final amplifier is offered
directly to the Y-amplifier of the basic oscilloscope
via terminals IBU-Y
and 17BU-Y. The trigger-
amplifier receives the same voltages via R236 and
R237 next to terminals 16BU-Y and 32BU-Y.
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