Tektronix CA PLUG-IN Instruction Manual page 12

by the MODE switch. With the MODE switch
in the A ONLY o r
m ultivibrator is held in one of its two possible
States by returning one grid to a positive
voltage and the other grid to a negative voltage.
F o r example, in the A ONLY position the grid
o f V3375A is held positive and this half of the
multivibrator conducts while the grid of V3375B
is held negative and this half is cut off. When
V3375A is conducting the cathode is above
ground which causes V3384B to conduct and it
in turn pulls the grid of V3393B toward ground
lowering the plate voltage of V4334 and V4354.
This reduced plate voltage cuts off the following
stage (V4364 and V4374) and the B-channel
am plifier is held in a non-conducting state.
The converse is true of the A-channel am plifier.
The grid of V3384A is near ground potential
with reduced plate current, therefore, the plate
o f V3384A and consequently the grid of V3393A
are permitted to become m ore positive thus
providing plate voltage for V3334 and V3354.
The A-channel am plifier then conducts.
A L T E R N A T E
Turning the MODE switch to the ALTE R NATE
Position returns both grids of the multivibrator
to a negative potential.
multivibrator. At the end of each sweep cycle
a negative-going trig g e r is generated and is
coupled to the m ultivibrator through the T rig g er
Coupling Diode V3382.
the multivibrator to " flip "
state to the other. This alternately switches
the am plifiers on and off. The switching rate
is now determined by the repetition rate of
the sweep.
CHOPPED
Turning the MODE switch to the CHOPPED
3-2
B O N LY position the
It is then a bistable
Each trigger causes
from one stable
Circuit Description - Type CA
Position returns both grids of the multivibrator
to a positive voltage and the multivibrator
fre e runs at a rate determined by the time
constant of the grid circuits. The two amplifiers
are alternately cut off and allowed to conduct
at the free-running rate of the multivibrator.
ADDED ALGEBRAICALLY
Turning the MODE switch to the ADDED
ALG E B R A IC ALLY position returns both grids
of the multivibrator to a negative voltage. Both
sides of the multivibrator (V3375) are held
sufficiently negative so that incoming triggers
have no effect on the multivibrator grids.
The cathodes of both halves of the multivibrator
follow the grids down, driving V3384A and
V3384B to cut off. With V3384A and V3384B
cut off the plate voltage rises, carrying the
grids of the following stages, V3393A and V3393B
with it. The cathodes of V3393A and V3393B
follow the grids up.
up, both am plifier channels conduct equally
in the absence of any Signal.
Note
Plate voltage fo r the input ampli­
fie r stages of both channels
supplied by the cathodes of either
V3393A or V3393B.
Under the conditions described above Signals
applied to both inputs w ill be amplified equally
by either channel. Algebraic addition of the
Signal occurs at the grids of the output stage,
V4383. In phase input Signals
phase input Signals subtract, at the grid of
each tube if the polarity switches are at the
same setting.
When the cathodes are
is
add, out of
AA