Tektronix 434, Instruction Manual, Page: 44 / 222

C irc u it D e s c rip tio n —
C han nel 1 D io d e G ate
C U R R E N T P A T H
R E V E R S E -B IA S E D D IO D E S
V e rtic a l
signal to
D e la y -L in e
D riv e r Stage
Fig . 3-5. E ffe c t o f D io d e G ates on signal p a th (s im p lifie d p a th ). C o n d itio n s sh o w n f o r C H 1 m o d e o f o p e ra tio n .
S w itch in g M u ltiv ib ra to r stage through R435 and C R 428 or
CR426. F or exam ple, if Q 420 is co n d u ctin g , cu rre n t is
supplied to Q 420 through C R 426. The c u rre n t flo w
th ro u g h c o lle c to r resistor R 420 drops the C R 405-C R 406
cathode level negative w ith respect to the cathodes o f
C R404 & C R 408, so the Channel 1 D iode Gate is blocked,
as fo r Channel 2 o n ly operation. The signal passes through
the Channel 2 D iode Gate to the D elay-Line D river.
The alternate-trace sync pulse is applied to Q 435
through C 430 at the end o f each sweep. This d iffe re n tia te d
negative-going sync pulse m o m e n ta rily in te rru p ts the
c u rre n t through Q 435, and b o th Q 420 and Q 425 are turned
o ff. When Q 435 tu rn s on again a fte r the alternate-trace
sync pulse, the charge on C425 determ ines w hether Q 420
or Q 425 conducts. F or exam ple, when Q 420 is co nducting,
C 425 is charged m ore p o sitive ly on the CR426 side to the
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