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Circuit Description - HP AR Operating And Servicing Manual

Wide band amplifier
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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-

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460ar