DESCRIPTION
General Electric Test Amplifier Model
4EX16A1O uses a single Integrated Circuit
module for operation as a high impedance m
amp Ii f ier . lYhen used wi t h RF Probe
19C3 1137OG1, the Test Amplifier can be corl-
nected to Test Set Models 4EX3A1O & 11 (or a
standard multimeter) to function as a high-
sensitivity RF voltmeter.
The amplifier and probe are designed
for measuring the gain of receiver front end
and IF circuitsr oscillator injection volt-
ages, and for measuring RF leve1s in other
RF circuits. The amplifier may also be used
for amplifying low level audio signals.
OPERATION
All operating controls and the input
and output binding posts are conveniently
Iocated on the front of the amplifier. The
binding posts are spaced for use with a dual-
banana plug if desired.
GAIN SELECTOR
Gain selector switch SlOOl selects the
Xl (unity) , X10 and X5O amplif ier ranges,
and also turns the amplif i.er on and of f .
BAI"ANCE
Balance potentiometer R1OOZ is used to
set the 4EX3A1O (or multimeter) on zero be-
fore maklng measurements. with the Test set
and RF Probe connected to the anplifier and
the gain selector on X5O, R1O02 is adjusted
for zera meter reading on the Test Set or
multimeter.
ATTEI\TUATOR
Attenuator RlOOl controls the input
level to the Test Amplifier. To obtain
actual gains of XI, X10 or XbO, Rl0O1 must
be turned fully clockwise to the CALTBRATE
position.
References to symbol numbers mentioned
in the following text may be found on the
appricable outline Diagrailr schematic Dia-
gram or Parts List (see Table of contents).
CIRCUIT ANALYSIS
TEST AMPLIFIER
The basic amplifier circuit consists
of Integrated Circuit module IC-I and 8s-
LB I _40978
sociated circuitry mounted on printed wiring
boards A1OO1. IC-I is a high performance,
operational amplifier whose gain is con-
trolled by three feedback circuits. The
feedback circuits are selected by GAIN switch
S10O1. Resistors RB and R9 form the Xl
(unity) feedback loop; resistors R6 and R7
form the X10 feedback loop, and R4 and R5
form the X50 feedback loop. Instructlons
for setting potentiometers R5, R7 and R9 are
contained in the Maintenance section of this
manual (see Tab1e of Contents).
The input is coupled through ATTENUATOR
R1OOI and a voltage divider network (nf and
R2) to terminal 5 of the IC. The output is
taken from terminal 10 and applied to the
feedback loops and the output terminal.
Battery voltage (L4 volts) is applied to the
IC through terminals 11 (+) and 6 (-).
Terminal 4 connects to ground through R3.
A small difference in potential called
the "offset" voltage is present at terminal
10 regardless of the input voltage applied
to IC-l. This voltage can be cancelled out
by BAI"ANCE potent iometer R1002 so that the
Test Set or multimeter can be set on zeta.
Instructions for setting the BAI"ANCE control
are contained in the OPERATION section of
the manual as listed in the Table of Con-
tents.The amplif ler may also be used f or 8fi1-
plifying audio signals in the DC to z0-kEz
range. The audio frequency response of the
amplifier at the different gain levels is
shown in Figure 1.
RF PROBE
RF Probe 19C31137OG1 is a highly sen-
sitive, uncalibrated probe for detecting RF
s ignals in the 5-MIIZ to 500-MHz range .
Point-contact diodes are used in the probe
for better sensitivity. A curve showing
the frequency response of the probe is shown
in Figure 2.
The probe is terminated in a dual-ba-
nana plug that connects to the Test Amplifier.
The probe may also be connected directly to
a rc oscilloscope for checking RF levels.
As an aid to the servi.ceman in trouble-
shooting RF clrcuits, a calibration proc€-
dure is provided for calibrating the RF
Probe (see Table of Contents).
TIAIilTENANCE
DISASSEMBLY
To disassemble the amplifier for s€r-
vicing, remove the two Phillips-head screws
in the front of the nameplate and carefullyI
