Table of Contents
Advertisement
•
Models 461A/462A
SECTION IV
THEORY OF OPERATION
Section IV
•
4·1. GENERAL DESCRIPTION.
4-2. The Models 461A and 462A Amplifiers are
essentially identical. In the Model 462A some of the
component values are changed slightly to improve its
pulse response. In this section both instruments will
be presented in terms of the Model 461A.
4·3. Figure 4-1 shows a simplified block diagram of
the Model 461A. The amplifier is a five stage,
stagger-tuned,
cascaded
amplifier
with
emitter
follower input and output stages. The gain is switched
from 40 dB to 20 dB by attenuating the input by 20
dB. The power supply is a conventional series
regulated supply with +15 volt and -IS volt outputs.
4·4. AMPLIFIER CIRCUITS.
4-5. Figure 5-12 shows the schematic diagram of the
Model 461A. A3Q3 is the input emitter follower,
matching the 50 ohm input impedance to the input
impedance
of the amplifier. Transistors A3Q4
through A3Q8 constitute a live stage, RC coupled,
cascaded amplifier. Each stage has a gain of 8.4 dB. 2
dB is lost in the input and output emitter followers,
giving the amplifier a total gain of 40 dB.
4-6. Each stage has an an LR feedback circuit with
an adjustable inductor. The feedback circuit in each
stage controls the overall gain of the amplifier at a
different frequency
l
so the amplifier must
be
stagger-tuned, There is some interaction between the
stages at certain frequencies. A3Q9 is the output
emitter follower, and it matches the amplifier output
to
a
50 ohm output impedance.
4-7. POWER SUPPl Y.
4-8. The power supply generates +15 volts and -IS
volts bias supply to the amplifiers. Breakdown diode
A2CR3 establishes a IS volt reference. Control
transistor
A2Q2
detects differences between the
reference voltage and the supply output, and its
output controls the series regulator Ql.
•
IINPUTI
IOUTPUT I
ATTENUATOR
->
EMITTER
--->
AMPLIFIERS
--..-.
EMITTER
,
~
,
,
FOLLOWER
FOLLOWER
AI
04-08
~
03
09
~
I
I
I
PRIMAR)'
I
o
POWER 8 GAIN
SWITCH
,
51,53
\
\
\
SERIES
PRIMARY
REGULATED
!
POWER
POWER SUPPLY
OJ -02-
.'_L.",'''"
I
Figure 4-1. Simplified Block Diagram
4-1
Advertisement
Table of Contents
