Model 450A
SECTION I
GENERAL
INFORMATION
Sections
Iand
II
Paragraphs
1-1
to
2-7
1-1.
DESCRIPTION.
1-2.
The
Model 450A
is
a
general-purpose,
stabi-
lized,
fixed-gain
amplifier
for
use
with
low-level
signals
from
2
cps
to
2
mc.
It
provides
two
calibrated
gain
factors,
lOX
(20 db) and 100X (40 db),
selectable
by atoggle switch on
the
front
panel.
Each
gain
factor
is
accurate
to
within ±
1/8
db in the audio
frequency
range;
frequency
response
is
given in
the
table
of
specifications
(figure
1-1).
Principal
characteristics:
stable
gain with
smooth
attenuation
beyond
rated
fre-
quency
range,
wide
frequency
range,
low
distortion.
1-3.
Typical
uses
include
increasing
the
sensitivity
of
ac
test
equipment
(voltmeters,
oscilloscopes,
bridges,
etc), obtaining
larger
signals
across
lower
impedances
in
test
bench
setups
and
permanent
system
installations.
An
electronically-regulated
power
supply
and
large
amounts
of
degenerative
feedback
around
the
entire
amplifier
circuit
provide
very
re-
liable
and
stable
operation
in
case
of changing
line
voltage,
load
resistance,
or
tube
characteristics.
1-4.
The
amplifier
is
constructed
on a
single
chassis
with
removable
cover
and bottom
plate.
A
leather
carrying
handle
is
provided
on
the
left
side
of
the
cabinet
model.
The
front
panel
is
finished in
light
grey
enamel;
the
rest
of
the
cabinet
is
finished in
dark
grey
wrinkle
paint.
Operating
controls
and
ter-
minals
consist
of
toggle-type
power
and gain
switches
and binding
post
type
input and output
terminals
on
the
front
panel.
Binding
posts
are
spaced
3/4
inch
on-centers
to
receive
dual
banana-plug
connectors.
The
power
cable
is
permanently
attached
to
the
rear
of
the
amplifier
and
is
terminated
in a
3-prong,
grounding-type
plug. A
fuse
is
provided
on
the
rear
and
can
be
replaced
externally.
1-5.
APPLICABLE
LITERATURE.
1-6.
This
handbook
contains
complete
operating
and
servicing
instructions
for
the
450A
Amplifier
and
conforms
to
the
format
specified
in MIL-M-5474C.
)
SECTION
II
OPERATING
INSTRUCTIONS
)
2-1.
INCOMING
INSPECTION.
2-2.
MECHANICAL. When unpacking
the
amplifier,
inspect
it
for
any
sign
of
physical
damage.
If
the
cabinet
is
damaged,
remove
cover
and bottom
plate
and
inspect
chassis
parts
for
further
damage.
Re-
port
all
damage
to
the
carrier
and keep
amplifier
intact
for
inspection
by
carrier
and
insurer.
All
in-
struments
shipped
by
the
Hewlett-Packard
Company
are
insured
against
shipping
damage.
See
Warranty
at
rear
of
manual.
2-3.
ELECTRICAL.
Electrical
inspection
consists
of
testing
certain
electrical
characteristics
of
the
amplifier
to
determine
that
it
functions
normally
after
having been
stored
or
transported.
Only
one
test
is
required;
full
instructions
are
given in
paragraph
4-20
steps
athrough f.
2-4.
INSTALLATION.
2-5.
INPUT CONNECTIONS.
The
amplifier
can
be
connected
to
a
signal
source
through
either
twisted
pair
leads
or
shielded
cable.
Keep input
leads
as
short
as
possible
to
avoid
excessive
capacitive
shunt-
ing of
the
signal
source.
If
necessary,
use
coaxial
cable
to
prevent
unwanted
signal
pickup
from
stray
electric
and magnetiC
fields.
00
NOT
connect
the
amplifier
input
to
circuit
potentials
greater
than
00001-1
400
volts
unless
an
externall-j..lfcapacitorhaving
suf-
ficient
voltage
rating
is
used
in
series
with the input
terminals.
2-6.
OUTPUT CONNECTIONS.
The
amplifier
output
can
be
connected
through any convenient
lead
set
or
cable.
The
low output
impedance
of
150
ohms
permits
shielded
cable
to
be
used
freely
without
capacitive
loading
in
the audio
range
and
permits
twisted
pair
leads
to be
used
with much
less
effect
from
stray
fields.
The
amplifier
is
designed
to
be
used
with
resistive
loads
of 3000
ohms
or
more.
Loads
below
3000
ohms
reduce
amplifier
gain bandwidth, and
maxi-
mum
output voltage
available.
For
higher
frequencies,
the
load
must
have
small
capacitive
reactance
topre-
serve
full output
signal
quality
and
stability.
DO
NOT
connect
the
output
terminals
to
dc
potential
of
more
than
+50
or
-300
volts,
or
output
capacitor
ratings
will be
exceeded.
2-7.
CONSIDERATION FOR LOW SIGNAL LEVELS.
When amplifying
low-level
signals
it
may
be
necessary
to
eliminate
an
electrical
ground
loop
formed
by
the
power
cable
ground
lead
and
signal
ground
lead
between
two
instruments.
If
this
electrical
path
is
completed
(typically a
combination
of
the
signal
groundand
power
line
ground
leads
do),
line
frequency
currents
flow in
the
signal
ground
lead
and develop
voltages
across
the
leads
which
are
in
series
with
the
desired
signal.
To
1-1
2-1
