positive
voltage is
required
at
the
grid
of
VI
10
A
which
is
high
enough
to cause plate
current
to
flow.
The
positive
voltage
for
return
ing
the
multivibrator
to
its
quiescent
state
is
supplied from
the time-base
generator
when
it
has
completed
its
sweep.
The
STABILITY
and PRESET
controls
adjust
the
grid voltage
of
VI
10
A
near
the
point
of
free running.
Time-Base
Generator
The
time-base
generator
is
a Miller
integrator
circuit.
The
circuit includes disconnect
diodes
V150A
and
V150B,
cathode-follower
V160A,
timing
capacitor
C160
and
the
Miller
tube,
V160B. In
the
quiescent state
between
sweeps,
the
plates
of
diodes V150A
and
V150B
rest
at
-2.5
volts.
Very
little
current flows
through
V150B
to
the
grid
circuit
of
V160B,
and
the
grid
of
V160B
rests
at
-2.5
volts.
More
current
flows
through
V150A
so
that
its
cathode
is
about
.5
volt
lower
at -3
volts.
The
timing
capacitor,
Cl
60,
which
is
connected
between
these
two
points, therefore has
a
charge
of
about
.5
volt.
The
grid
of
cathode-follower
V160A
is con
nected
to
the
plate
of Miller
tube
V160B
through
neon
glow
tube
B160.
The
grid
of
V160A
therefore follows
the
plate
changes of
V160B
but
remains
55
volts
below
the
plate.
Network
C161,
R161, improves
the
risetime
of
the
circuit.
The
-2.5
volt
bias on
the
grid
of
V160B
places
the
tube
in
the
class
A
region
of its
operating characteristic,
where the
plate-to-
cathode
voltage
is
inversely
proportional
to
the
grid
to
cathode
voltage.
The
plate
rests
at
about
+55
volts.
The
negative
step
from
the
multivibrator
to the
plates
of
diodes
V150A
and
V150B
lowers
the
plates
below
their
cathodes
and
they
no
longer
conduct.
The
Miller-tube
grid,
and
the
cathode
follower
are thus
released
to
seek
their
own
voltage
levels.
The
grid
of
Miller
tube
V160B,
which
is
returned
to
-150
volts
through
R150,
starts
negative.
When
the
grid
starts
negative
the
plate starts
positive
carrying cathode-follower
V160A
grid
and
cathode
positive.
This
raises
the
top
end
of
C160
positive
which
thus
tends
to
prevent
the
Miller
tube
grid from going negative.
The
gain
of
the
Miller
tube
as
a
class-A
amplifier is
so
high
that
the
plate
signal
coupled
back
through
charging
capacitor
C160
keeps
the
grid
voltage
constant
within
a
fraction
of
a
volt.
Meanwhile, C160 is
charging
with
current
through
R150 from
the
-150-volt
bus.
Since
the
grid
of
V160B
remains
constant
within
a
fraction
of
a
volt,
the
current
through
R150 remains
constant,
and
C160
thus
charges
at
a
constant
rate.
As C160 charges
the
voltage
of
the
upper
end
therefore
rises
linearily.
Any
departure
from
a linear
rise
of
the
cathode
of
cathode
follower
V160A
will
result
in
a change
in
Miller-tube grid
voltage
in
the
direction
that
will
correct
for
the
error.
A
bootstrap
capacitor, C165,
increases
the
plate
current
in
V160B
at
the
higher
sweep
speeds
to
help
maintain
a
linear
voltage
rise.
The
linear
rise
of
the
cathode
of
V160A
is
used
as
the
time-base
sawtooth.
Charging
capacitor
C160
is selected
by
means
of
a
step
switch,
SW155,
labeled
TIME/CM
on
the
front
panel. Charging
resistor
R150
is
also
selected
by
the
TIME/CM switch
so
that
both
the
size
of
the
capacitor
being
charged
and
the
current
charging
the
capacitor
can
be
selected
to
cover
a
wide
range
of
sawtooth slopes.
The
cathode of
V160A
continues
to
rise
linearly
until
a
positive
step
from
the
multi
vibrator, V120B,
returns
the
disconnect
diode
plates
back
to
their quiescent state
raising
the
Miller
tube
grid.
When
the
Miller
tube
grid
rises,
its
plate
drops carrying
cathode
follower
V160A with
it
until
its
cathode
clamps
again
through
V150A
at
the
quiescent
level
of
-2.5
volts.
The
Miller-tube
plate
will
always
rest
at
about
+55
volts
after
the
sweep,
because,
as
V150A
begins
to
conduct,
its
plate
drops
slightly.
This
reduced plate voltage
allows
the
Miller-tube
grid
to
go
slightly
more negative,
stopping the
fall
in
plate
voltage.
Sawtooth
Amplitude
The
positive
step from
multivibrator
V120B,
which
stops
the
sweep, occurs
when
a
positive
voltage is
delivered
to the grid
of
multivibrator
V110A.
The
time-base
sawtooth
is
applied
to
the
multivibrator
through
cathode
followers
V140A
and V140B from
a
tap
on
the
cathode
load
resistor
of
V160A.
This
tap
is adjustable
by
means
of
potentiometer
R156, labeled
Saw
tooth Amplitude,
a
screwdriver adjustment.
When
the
voltage
of
this
tap
is
properly
set,
the
sawtooth
will
terminate
when
the
spot
has
passed
the
right-hand limit
of
the
graticule.
C130
on
the
grid
of
V140B
retards
the
return
3-4
Circuit
Description
- Type
515/515A