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HP 120A - Page 39

HP 120A
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Sect.
Ill
Page
5
It
is
desired
to
prevent
triggers
from
initiating
an
other
sawtooth
until
the
integrator
has
time
to
dis
charge
the
timing
capacitor
and
recover
fully.
The
resistance-condenser
combination
in
the
cathode
of
the
hold-off
cathode
-follower
accomplishes
this
by
permitting
only
a
slow
decay
on
the
grid
voltage
of
the
start-stop
trigger
to
a
voltage
level
2
volts
above
the
lower
hysteresis
limit.
This
level
is
set
by
the
sweep
stability
control
so
that
negative
triggers
from
the
trigger
generator
will
reach
below
the
lower
hys
teresis
limit
to
trigger
the
start-stop
trigger
gene
rator
thus
initiating
a
sweep.
The
sweep
length
adjustment
in
the
grid
circuit
of
the
Hold-Off
Cathode
Follower
adjusts
the
voltage
sup
plied
to
the
circuit
and
thus
the
length
of
time
that
it
will
take
the
sweep
to
reach
its
upper
hysteresis
lim
it.
The
sweep
stability
control,
in
the
cathode
cir
cuit
of
the
Hold-Off
Cathode
Follower
adjusts
the
bias
on
the
Start-Stop
Trigger.
This
is
adjusted
to
place
the
voltage
just
above
the
lower
hysteresis
limits.
g.
Gate
Inverter
-
Another
function
of
the
Start
-
Stop
Trigger
is
to
furnish
a
pulse
to
blank
and
unblank
the
Cathode-ray
Tube.
Since
both
a
posi
tive
and
a
negative
pulse
is
needed,
a
phase
inver
ter
is
inserted
in
the
signal
path.
The
positive
un
blanking
pulse
is
condenser-coupled
to
the
grid
of
the
Cathode-ray
Tube.
This
ac-coupled
path
will
turn
the
Cathode-ray
Tube
on
rapidly,
for
fast
signals.
However,
being
only
ac-coupled,
it
does
not
furnish
any
voltage
to
hold
it
on
for
the
duration
of
the
sweep.
This
is
the
function
of
the
negative
gate
signal.
The
signal
from
the
plate
of
the
phase
inverter
is
fed
di
rectly
into
the
section
of
the
High
Voltage
Power
Sup
ply
that
is
connected
to
the
cathode
of
the
Cathode
-
ray
Tube.
The
cathode
is
also
connected
to
the
re
sistor
string
that
controls
the
regulation
of
the
os
cillator
in
the
High
Voltage
Power
Supply.
The
ne
gative
pulse
is
fed
into
this
regulator
string
at
a
slow
enough
rate
that
the
regulator
can
take
control
keep
ing
the
-2250
volt
cathode
supply
constant.
This
re
quires
that
the
high
voltage
oscillator
put
less
energy
into
the
cathode
winding
of
the
high
voltage
transfor
mer.
The
grid
winding
being
tightly
coupled
also
re
ceives
proportionally
less
energy
and
its
de
output
changes
by
the
amount
of
the
applied
gate
signal.
Since
this
supply
provides
the
de
reference
for
the
cathode-ray
tube
grid,
a
path
has
been
provided
for
the
de
coupling
of
this
unblanking
signal.
3-6
LOW
VOLTAGE
POWER
SUPPLIES
The
Low
Voltage
Power
Supply
consists
of
two
sepa
rate
supplies
furnishing
plate
voltages,
a
regulated
de
filament
supply,
and
the
usual
ac
filament
supplies.
a.
Plate
Voltage
Supplies
in
the
Low
Voltage
Power
Supply
-
The
Low
Voltage
Power
Supply
contains
two
plate
voltage
supplies,
one
furnishing
+
380
volts
and
+100
volts
and
the
other
furnishing
-150
volts.
The
positive
plate
supply
voltage
supply
consists
of
a
transformer,
a
5Y3
rectifier,
a
6U8
(pentode
sec
tion)
amplifier,
and
a
12B4A
control
tube
in
the
usual
regulated
power
supply
configuration
followed
by
a
6U8
(triode
section)
cathode
follower.
This
supply
has
a
+
380
volts
regulated
and
a
+100
volt
low-im
pedance
supply
from
the
cathode
of
the
cathode-fol
lower.
The
negative
voltage
supply
consists
of
a
transformer,
a
6X4
rectifier,
a
6AU6
amplifier,
a
5651
voltage
re
ference
tube
and
a
12B4A
control
tube
in
the
usual
regulated
power
supply
configuration.
This
supply
has
a
single
output
at
-150
volts.
This
supply
is
used
for
reference
and
in
addition
as
a
negative
return
for
the
circuits.
b.
Transistorized
Filament
Supply
-
This
supply
furnishes
regulated
+
24
volts
for
use
as
a
fila
ment
supply
for
two
twelve-volt
critical
filament
volt
age
tubes
in
series.
These
tubes
are
the
first
two
tubes
in
the
Vertical
Amplifier.
Any
change
in
the
filament
voltage
of
these
tubes
will
be
greatly
ampli
fied
and
appear
as
drift
on
the
face
of
the
cathode-ray
tube.
By
supplying
this
filament
voltage
from
a
regu
lated
source
the
possibility
of
drift
due
to
the
filament
supply
is
greatly
reduced.
The
supply
consists
of
a
transformer,
a
1N1081
silicon
power
rectifier,
and
two
pnp
type
transistors,
one
CTP1113
and
one
TS-600C,
as
regulators.
The
CTP1113
is
operated
with
a
grounded
emitter
acting
similar
to
a
series
tube
in
a
conventional
regulator
circuit.
The
TS-600C
is
an
emitter
follower
driving
the
CTP1U3,
and
acts
as
the
control
amplifier.
Reference
voltage
is
obtained
from
the
-150
supply
with
a
1%
divider
.
3-7
HIGH
VOLTAGE
POWER
SUPPLY
The
High
Voltage
Power
Supply
consists
of
a
Hartley
oscillator,
two
separate
secondary
winding
supplies
and
two
tube
regulators.
a.
Hartley
Oscillator
-
The
Hartley
oscillator
con
sists
of
a
6AQ5
oscillator
tube,
and
a
tapped
winding
on
the
high
voltage
transformer
which
is
se
ries
fed
from
tire
+
380
volt
supply.
This
circuit
os
cillates
at
approximately
60
kc.
This
supply
has
two
separate
secondaries
and
two
separate
5642
rectifier
tubes.
One
of
these
supplies
is
connected
to
the
grid.
The
INTENSITY
and
Intensity
Limit
potentiometers
in
series
with
the
ground
return
of
this
supply
deter
mine
the
voltage
on
the
intensity
grid
and
thus
the
brilliance
of
the
pattern.
The
positive
gate
unblanking

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