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and
the
voltage
at its plate starts
of
V7350A
and
grid
of
V7350B,
the
rise
in
voltage
at
the
plate
of
V7350A
carries
the
With
the
grid
voltage
of
V7350B
going
up,
to
conduct
the
cathodes
of
both
tubes
begin
to
follow
the
action
of
the
grid
of
V7350B;
hence
the
cathode
voltages
start
going
up.
With the grid of V7350A down and its cathode
up,
this
tube
stops
conducting.
As
V7350B
conducts,
its plate voltage drops,
creating
a
negative-going step at its output. This transition
occurs
rapidly, regardless of how slowly the
When the signal applied to the grid of V7350A
starts
in
the
opposite
direction
the
action
described inthe preceding: paragraphs reverses
itself.
That
is,
V7350A will start to conduct
once
more,
while V7350B is cut off--causing
the
circuit
to
revert
to
its
original
state.
The operation of the Schmitt Trigger is exactly
the
same
for
both +
and
-
positions
of the
TRIGGER SLOPE switch.
However,
the polarity
at
the
output
of
the
Trigger
Amplifier
is
reversed
between the +
and - settings of the
TRIGGER
SLOPE
switch
with
respect
to
a
certain
point
on
the
triggering
signal.
This
causes
triggering to occur at different points
on the waveform being observed.
When the TRIGGER SLOPE switch is in the
+
positions triggering occurs on the positive-
going portion of the waveform and the display
starts at that point. When the TRIGGER SLOPE
switch is in the - positions triggering
occurs
on the negative-going portion of the waveform
and the display starts at a point on the negative
The
TRIGGERING
MODE
switch,
SW7040,
selects
the
type,
or
mode,
of triggering.
In
dc-coupled
from
the
TRIGGER
INPUT
to
the
Trigger
Amplifier,
which
in
turn is dc-
coupled
to
the
grid
of
V7350A
the
Schmitt
Trigger.
R7240
isolates
the
plate
circuit of
V7040A from
the
capacitance
of
the
switch;
R7250 isolates the grid circuit of V7350 from
In the AC position of the TRIGGERING MODE
Switch,
capacitor C7020 is connected into the
input
circuit; this of course, removes any dc
component of the waveform. The Trigger-Input
Amplifier, however, is still dc-coupled to the
In
the
AUTO.
position of the TRIGGERING
MODE switch, the Schmitt Trigger is converted
from
a
bistable
configuration
to a recurrent
configuration, This is accomplished by coupling
the grid circuit of V7350B to the grid circuit
of V7350A via R7370.
In addition,
the dc coupling
between
the
Trigger-Input
Amplifier
and the
Schmitt Trigger is removed when the switch is
The addition of R7370 to the circuit causes
the Schmitt Trigger to free-run in the absence
of a triggering signal.
For example, assume the
grid of V7350A is just being driven into cut-off.
The voltage at
the
plate
of
V7350A starts to
rise,
carrying
with
it
the
grid
voltage
of
V7350B.
As the voltage at the grid of V7350B
rises, V7350B_
starts to conduct.
The
rising
voltage
at
the
grid of
V7350B
is
coupled
to
the
grid
of
V7350A
through
R7370.
The grid of V7350A is prevented from
rising immediately by the action of C7240, which
must be charged sufficiently to raise the voltage
As V7350A starts to conduct, its plate voltage
drops,
which
in
turn
lowers
the
voltage
at
the
grid
of
V7350B.
The voltage at the grid
of
V7350A
now
starts
dropping exponentially
toward
cutoff.
When
V7350A
reaches
cutoff
again,
the circuit has completed one cycle of
its
approximately 50-cycle voltage waveform.
The range of
voltage at the grid of V7350A
about
3
volts
when the circuit is used in the
cutoff, a triggering signal with a peak-to-peak
3-2
Circuit Description - Type T
AA
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