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R273
is
the
feedback
resistor for
the operational
am-
plifier
circuitry
including
IC215A and
its
discrete
output
stage.
The
signal
is
then applied
across
P21 3
providing
variable output attenuation.
R
1
25
is
a current limiting
resistor for
the
meter.
Power
Supply:
The
AC
enters
the
chassis
and
is
applied through
the
fuse to
the
power
transformer.
This
transformer
may
be
strapped
for
115
volt or
230
volt
operation;
instructions
for
doing
so are
found
in
the
INSTALLATION:
ELEC-
TRICAL
section.
The
center-tapped secondary
of
the
power
transformer
is
applied
to
two
pairs
of diodes,
CR601-604,
operating
as a
pair
of
full-wave
rectifiers
to
derive unregulated
voltages
of
approximately
+22.5
volts
DC.
The
outputs
of the
rectifiers
are
smoothed by
energy-storage capaci-
tors
C601
,
602
Most
of the positive regulator
is
contained
in
IC601
,
a
723C
voltage regulator.
IC601 contains a
stable
source
of reference voltage (nominally
7.15
volts),
an operation-
al
amplifier
to
compare
the output with the reference, a
series pass transistor to
drive the external
power
transistor
Q604,
and
a
current-limit
transistor.
The
reference vol-
tage
output
at
pin
6
is
filtered
by
C603
to
reduce
noise
and
is
introduced
to
the
(+)
input of the
opamp,
pin 5.
The
unregulated
positive
voltage
is
applied
to pins
1
and
12,
and
to
the collector of
series pass transistor
Q604,
operated
as
an
emitter-follower.
The
output current of
Q604
passes
through R601,
which
develops
a
voltage drop
proportional to the current
through
it.
This
voltage drop
is
sensed across
pins 2
and
3 of
IC601
.
If it
exceeds
ap-
proximately
0.55
volts,
the
internal
current
limit transis-
tor turns
on and
prevents
further
increase
in
output cur-
rent, thus
providing
short-circuit protection
for
Q604.
The
output
is
sensed
by
the voltage divider
R602, 603,
P601
,
and
is
applied
to
the
(-)
input of the internal
opamp
(pin 4).
The
voltage divider reduces the output voltage
until
it
is
equal
to the reference voltage.
The
output vol-
tage
is
therefore held
at
a multiple
of the
reference vol-
tage by
means
of
feedback.
This
multiple (and therefore
the output voltage)
is
adjusted
by means
of P601
.
C604
frequency-compensates
the
interna!
opamp
to
prevent
high-frequency
oscillations.
Further stabilization
is
pro-
vided by
C605
across
the output of the regulator.
The
-15
supply
is
generated by
means
of a
741C opamp,
IC602,
in
conjunction with
external
transistors.
IC602
is
connected
as
an
inverting, unity
gain amplifier with
input
resistor
R607
and feedback
resistor
R606.
Thus, the
negative output
tracks
changes
in
the
positive
output.
The
positive
power
supply
for
IC602
is
provided
by
IC601
.
IC601 contains
an
internal
6.8
volt
zener diode,
which
drops the
+15.7
volt
output of the
internal series
pass transistor to
approximately +9
volts.
This
voltage
is
available
at
pin 9.
Negative
supply voltage
for
IC602
is
provided by the unregulated negative supply.
This
scheme
assures that
the
total
supply voltage
for
IC602
can
never
exceed
IC602
's
maximum
36
volt
rating.
IC602
drives a
conjugate
emitter follower,
Q602,
603, R604.
As
in
the case
of the positive
supply, the
output current
is
dropped
across
R605, and
if
the
voltage
across
R605 exceeds approximately 0.55
volts,
Q601
turns
on
and
shunts drive current
away
from
Q602,
simul-
taneously activating
the protective current limiting cir-
cuitry inside
IC602 which
limits
IC602's
own
output cur-
rent to a safe level
FACTORY
SERVICE
Factory service
is
available through the
life
of
the
418
from the address
above.
During
the
warranty
peri-
od, no charge
will
be
made
for parts or
labor, subject to
warranty
conditions.
After expiration
of
the warranty,
a reasonable
charge
will
be
made
for parts,
labor,
and
packing.
In
any
event,
transportation
charges (which
are
usually quite nominal)
shall
fall
on the customer.
Before returning
any
unit
for
repair,
please write
or
telephone
for
instructions, stating
the trouble
experienced.
Often
a
problem can be
solved
by
consultation, saving
everyone
the delay,
inconvenience, and expense
of
ac-
tually returning
the
unit.
SHIPPING INSTRUCTIONS
If
the original
packing
material
is
available,
it
should
be employed.
Otherwise,
a carton
of at least
200
lbs
bursting
test
should
be
obtained
which
is
no
smaller
than
22
x
15x9
inches.
The assembly
should
be packed
so that
there
is
at
least
1-1/2"
of
packing
material protecting
every
point.
Cushioning
material
such
as
Air-Cap, Bubble-Pak, foam
"popcorn",
or fibre
blankets are
acceptable.
Folded
newspaper
is
not suitable.
Blanket-type material
should be
tightly
wrapped
around
the assemblies
and taped
in
place
to
prevent the
unit
from
shifting
out of
its
pack-
ing
and
contacting
the walls of the carton.
The
carton should be
packed evenly and
fully
with the
packing
material
filling all
voids
so that
the
units
can-
not
shift in
the carton.
Test
for this
by closing
but not
sealing the carton
and
shaking vigorously.
If
the
unit
can
be heard
or
felt
moving,
use
more packing.
The
carton should be well-sealed with
3"
reinforced
sealing tape applied
across
the top
and bottom
of the
box
in
an
"H"
pattern.
Narrower
or
parcel-post type tapes
will
not
withstand the
stresses
applied
to
commercial
ship-
ments.
The package
should
be marked with
the
name
of
the
shipper
and
the words,
in
red,
DELICATE
INSTRUMENTS,
7
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