Hewlett-Packard AR Operating And Servicing Manual
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Several
amplifiers
can
be
cascaded
when
more
than
20
db
gain
is
desired.
The
maximum
gain
which
can
be
used
will
be
limited
by
the
effective
noise
generated
in
the
input
circuit
of
the
amplifier.
The
noise
figure
is
approximately
10
db.
When
amplifiers
are
cascaded.
the
rise
time
will
be
greater
than
that
of
a
single
unit
in
accordance
with
the
relation:
1/2
T • t
(n)
where:
T
is
total
rise
time
t
is
the
rise
time
of
a
single
unit
(3
X
10-9
sec.)
n
is
the
number
of
460
units.
The
total
rise
time
of
any
number
of
460
Amplifiers
in
conjunction
with
any
load
may
be
found
approximately
by
the
following
relation:
T
'"
[nt
2
+
(440C)2J
1/2
where:
)
2-5
CIRCUIT
DESCRIPTION
n •
number
of
460
Amplifiers
t -
rise
time
of
one
460
=
2.6
X
10-9
sec.
C •
total
shunt
capacitance
on
the
output
of
the
460
in
farads.
T =
total
rise
time.
The
Model
460AR
is
an
amplifier
which
has
a
very
wide
transmiss-
ion
band.
It
has
two
stages
with
five
tubes
in
the
first
stage
and
seven
tubes
in
the
second
stage.
The
grids
of
these
tubes
are
con-
nected
along
one
transmission
line
for
the
input
circuit
and
the
plates
of
the
tubes
are
connected
along
a
second
transmission
line
for
the
output
circ
uit.
A
wave
traveling
down
the
input
line
ex-
cites
the
grids
in
succession
and
half
of
the
corresponding
wave
generated
in
the
plate
circuit
travels
down
the
plate
line
toward
the
output
and
is
reinforced
at
each
successive
plate.
The
part
of
the
wave
in
the
plate
line
which
travels
in
the
reverse
direction
is
absorbed
by
a
termination
of
the
other
end
of
that
line.
By
the
time
the
wave
in
the
plate
line
reaches
the
output.
it
has
been
am-
plified
by
about
10
db.
The
second
stage
adds
another
10
db
to
make
a
total
of
20
db
gain
for
the
unit.
The
Model
460AR
will
amplify
pulses
with
an
extremely
short
rise
time
and
with
virtually
no
overshoot.
The
time
of
rise
of
the
am-
plifier
itself
is
approximately
3
millimicroseconds.
The
amplifier
has
an
amplitude
response
closely
matching
the
Gaussian
Curve.
which
is
the
ideal
transmission
for
pulse
amplifications
when
ring-
or
overshoot
cannot
be
tolerated.
-5-