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
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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