Circuit
Description-Type
453/R453
base controls conduction. A dual transistor, Q764, and a
dual diode,
D764,
provide temperature stability for the
comparator circuit.
0769
maintains a constant current
through the conducting transistor. Reference voltage for
the comparator circuit
is
provided
by
the
DELAY-TIME
MULTIPLIER
control,
R760.
The
voltage to
this
control
is
filtered by
R759-C759
to hold
it
constant and allow precise
delay pickoff.
The
instrument
is
calibrated
so
that the major
dial markings of
R760
correspond to the major divisions
of horizontal deflection
on
the graticule.
For
example,
if
the
DELAY-TIME
MULTIPLIER
dial
is
set to 5.00, the B
Sweep Generator
is
delayed
five
divisions of the A sweep
time before
it
can produce a sweep
(B
sweep delay time
equals
five
times setting of A
TIME/DIV
switch).
The
output sawtooth
from
the A Sawtooth Sweep Gen-
erator stage
is
connected to the base of 0764A.
The
qui-
escent level of the A sawtooth biases 0764A
on
and
its
collector
is
negative enough to hold
0772
in
the Delay
Multivibrator stage
in
conduction.
As
the A sweep output
sawtooth begins to
run
down, the base of 0764A also goes
negative. When
it
goes more negative than the
level
at
the base of
07648
(established by the
DELAY-TIME
MULTI-
PLIER
control), Q764B takes over conduction of the
com-
parator and 0764A shuts off.
This
also switches the Delay
Multivibrator stage to produce a negative-going reset pulse
to the B Sweep
Reset
Multivibrator.
When the A sweep resets, 0764A
is
again returned
to
conduction and Q764B
is
turned
off.
This
also resets the
Delay Multivibrator to produce a positive-going output
pulse.
If
the B sweep
is
still
running,
this
positive-going
pulse forces the B Sweep
Reset
Multivibrator to reset and end
the B sweep also.
Delay Multivibrator
The
Delay Multivibrator, Q768 and Q772, provides a
lockout for the B Sweep Generator circuit during the A
Sweep Generator reset and holdoff time
to
allow accurate
delayed-sweep measurements when the
DELAY-TIME
MULTI-
PLIER
dial
is
set near
0.
This
stage prevents the B Sweep
Generator
from
being triggered before the A Sweep Gen-
erator
is
triggered
(B
Sweep Generator
must
always be
triggered after the A Sweep Generator
is
triggered}.
This
circuit also produces a pulse which resets the B Sweep
Reset
Multivibrator stage after the delay period so the B Sweep
Gate
tunnel diode can be enabled to produce a sweep.
Transistors Q768 and
0772
are
connected as a Schmitt
bistable multivibrator.
O~iescently,
Q772
is
held on by the
negative
level
at
the collector of 0764A and
0768
remains
off.
The
circuit remains
in
this
condition
until
the incoming
A
Sweep switches the Delay-Pickoff Comparator
(see
Delay-
Pickoff
Comparator discussion). Then, the base of
0772
goes positive and
it
turns off.
At
the same time, the base of
0768
is
pulled negative by the collector
level
of
07648
and
it
turns on.
The
collector of
0772
goes negative and a
negative-going output pulse
is
coupled to the B Sweep
Reset
Multivibrator stage through
C77
4.
This
pulse resets the
B Sweep
Reset
Multivibrator which
in
turn
enables the B
Sweep
Gate
stage.
Sweep
Reset
Multivibrator
The
basic B Sweep
Reset
Multivibrator configuration and
operation
is
the same as for the A Sweep Generator.
How-
3-20
ever, several differences do exist.
The
B Sweep
Reset
Multi-
vibrator dos not have a sweep length network for variable
,,
sweep length or a Holdoff Capacitor and associated circuit
to reset the B Sweep
Reset
Multivibrator after the retrace.
Instead, the negative-going sweep
from
the B Sweep
Reset
Emitter
Follower, 0753,
is
conneded to the base of Q785
through
D7
48.
Diode
D7
48
is
forward biased when the
sweep voltage
at
the emitter of
0753
drops about 0.5 volts
more negative than the
level
at
the base of
0785
established
by
voltage divider
R784-R785
between +
12
volts and the
collector of 0775.
This
negative-going sawtooth turns
on
Q785 and
its
collector goes positive to switch the B Sweep
Gate tunnel diode,
D705
to
its
low-voltage state, which resets
the B Sweep.
0785
remains
on
and holds the B Sweep
Gate tunnel diode locked out
until
the B Sweep
Reset
Multi-
vibrator
is
reset by the Delay Multivibrator.
When the B Sweep
Reset
Multivibrator
is
reset by the Delay
Multivibrator,
0775
comes
on
and
0785
turns
off.
The
collector of
0785
goes negative and the B Sweep Gate
tunnel diode,
D705,
is
enabled.
The
state
in
which
D705
remains depends upon the B
SWEEP
MODE
switch and the
HORIZ
DISPLAY
switch. When the B
SWEEP
MODE
switch,
SW635,
is
set to the
TRIGGERABLE
AFTER
DELAY
TIME
position,
D705
is
biased
so
it
can be switched to
its
high-
voltage state by the next trigger pulse
from
the B Trigger
Generator. However,
if
the B
SWEEP
MODE
switch
is
set
to the B
STARTS
AFTER
DELAY
TIME
position, the setting
of the
HORIZ
DISPLAY
switch,
SW801
A,
determines opera-
tion of the B Sweep
Gate
tunnel diode.
In
the A position, the
B trigger pulses are blocked
in
the B Trigger Generator
circuit
so
the B Sweep Generator cannot be triggered and
does not produce a sweep.
In
the A
INTEN
DURING
B '
and
DELAYED
SWEEP
(B)
position,
-12
volts
is
connected
to the cathode of
D705
through
R786
and
R789.
This
voltage
pulls the cathode of
D705
negative enough so that
it
auto-
matically switches to
its
high-voltage state after
it
is
enabled
by the B Sweep
Reset
Multivibrator stage.
This
produces
a free-running B sweep
Reset
similar to the
no
trigger
AUTO
TRIG
mode
in
the A
Swe·ep
Generator. However, since
the B Sweep
is
reset (and automatically retriggered)
at
a
fixed point
on
the A sweep sawtooth, the display
is
rela-
tively stable.
The
best delayed sweep stability
is
provided
in
the
TRIGGERABLE
AFTER
DELAY
TIME
position, since the
B sweep
is
triggered by the trigger signal
in
this
mode .
B
Ends
A
Pulse
Amplifier
The
positive-going voltage as the B unblanking gate ends
is
coupled to the B
Ends
A
Pulse
Amplifier, Q734, through
C731
and
D731.
When the A
SWEEP
LENGTH
control
is
in
the B
ENDS
A position,
this
pulse saturates
0734
to
produce a negative-going ouput pulse
at
its
collector.
This
negative-going pulse
is
connected to the A Sweep
Reset
Multivibrator stage to reset the A sweep
at
the end of the
B sweep for maximum delayed sweep repetition rate.
HORIZONTAL
AMPLIFIER
General
The
Horizontal Amplifier circuit provides the output signal
to the
CRT
horizontal deflection plates.
In
all positions of
...-
the
HORIZ
DISPLAY
switch except
EXT
HORIZ,
the hori-
zontal deflection signal
is
a sawtooth
from
either the A
Sweep Generator circuit or the B Sweep Generator circuit.
@
To Next Page
Loading...
Need help?
General
