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Model 205AG Specifications
FREQUENCY RANGE : OUTPUT METER:
20 cps ta 20 kc in three decade bands: Calibrated in volts and dbm (0 dbm = 1 mw,
600 ohms). Full scale values 65 volts, 37 dbm.
Xl 20 cps ta 200 cps Reads on 600 ohm basis regardless of output
XlO 200 cps ta 2 kc impedance selected.
XlOO 2 kc ta 20 kc
Calibration covers approximately 270 degrees OUTPUT A TTENUA TOR:
on 6 inch diameter main dial. Provides 110 db in 1 db steps.
CALmRATION ACCURACY: Calibrated in dbm (0 db = I mw 1 600 ohms)
Within %2%at normal ambient temperatures. from -5 to + 8 dbm and in volts from 0 to 2 v
(Includes warm-up and changes due to aging rms. Voltage accuracy is :!:5% of full scale.
of tubes and components. )
Extends meter range to + 48 dbm and to 200 v
OUTPUT: rms in 5 db steps. Accuracy + 0. 1 db.
5 watts maximum into resistive loods of 50,
200, 600 and 5000 ohms. Output circuit is
balanced and center tapped --any terminaJ
may be grounded. POWER StJPPLY:
115/230 volts %10%,50-1000 cps, 150 watts.
:1 db 20 cps to 20 kc at output levels up to
Cabinet Mount: 20-3/4 in. wide, 12-3/4 in.
+ 30 dbm with output meter reading held at
high, 15-1/2 in. deep.
+ 37 db, :1. 5 db 20 cps to 20 kc at output levels
above + 30 dbm with output meter reading held
at + 37 db (reference 1000 cps).
Less than 1% at frequencies above 30 cps.
Approximately 1/6 load impedance with zero
attenuator setting. Approaches load impedance
with attenuator settings of 20 db or more.
More than 60 db below the output voltage or WEIGHT:
90 db below zero level (1 mw, 600 oluns), Cabinet Mount: 56 tbs, shippingweight 78lbs.
whichever is the larger. Rack Mount: 49 tbs, shippingweight 71lbs.
Table of Contents, Model 205AG
List of Illustrations and Tables
TABLE OF CONTENTS
~ ! Page
Section Page Section
GENERAL Inspection DESCRIPTION 1-1 IV MAIN ENANCE. IV-1
1-1 4-1 C binet Removal IV -1
1-1 4-2 be Replacement IV -1
4-3 Distortion IV -1
4-4 Cfl.pacitor Drive Lubrication .IV -1
II 2-1 Controls
OPERATING and Terminals.
INSTRUCTIONS ... 11-1 4-5 F1:equency Ca11bration Adjustment IV -1
4-6 O tPUt Level Meter Adjustment
~ IV -2
4-7 I put Level Meter Adjustment. IV-2
Oscillator Level Operation
Meter Operation .. ll-l
4-8 R placement of Lamp R11 ..IV -2
4-9 I termittent Output. IV -3
2-4 Input Level Meter Operation. .. ll-2
de ring P
rn CIRcurr DESCRIPTION m-l
3-1 General. llI-1 V-l
LIST OF ILLUsTRATIONs
Number Title Page Number Title Page
1-1 Model 205AG Audio Signal Generator . 1-1 3-1 Bloc k Diagram. m-l
2-1 Output Voltage Correction Factors 4-1
4-2 Botto~ V~ew View
Removed .. IV-4
when using Output Attenuators ... n-o IV-5
2-2 Input Level Meter Correction Curve . n-3 4-3 Schematic Diagram. IV-6
LIST OF TABLES
Number TUle Page
4-1 Troubleshooting Chart I. . IV-3
5-1 ReplaceableParts V-l
Model ~O5AG Sect. II Page 1
2-1 CONTROLS AND TERMINAILS and an unbalanced output may be obtained by con-
necting the~terminal to one of the output terminals
POWER ON with the captive link provided
This switch ccntrcls the power supplied tc the instru-
ment trom the power line. OUTPUT LEVEL
This meter indicates the voltage at the output ter-
LOAD ON minals when the IMPEDANCE switch is set at 600,
This switch is usedta cannect an intern 11laad acrass output attenuators OOth zero, and the instrument
the OUTPUTterminals. is loaded with the internalor an external 600 ohm
load. Under other oper~ting conditions the meter
INPUT may be used as a monitor to insure constant output
These terminals are the input for the audio fre- voltage .
quency INPUT LEVEL vacuum tube voltmeter in
the instrument. INPur LEVEL
This meter measures the voltage applied to the input
INPUT ATTENUATOR (DE) terminals and the range of the meter is controlled
This switch is the range switch for the INPUT LEVEL by the INPUT ATTENUATOR (DB) range switch.
meter and is calibrated in steps of 5 db from 0 to
40 db. FUSE
The fuseholder, located Dn the back of the chassis,
FREQUENCY RANGE contains the power line fuse. Refer ta the Table
The position of this switch indicates the multiplying of Replaceable Parts for the correct fuse rating.
factor to be used with the frequency dia! indication.
FREQUENCY Dial The three conductor power cable is supplied with a
This dial is calibrated in cycles per second. The oUt- NEMA approved three-prong plug. The third con-
putfrequencyis the frequency dial indication multi- ductor provides a chassis ground. An adapter may
plied by the FREQUENCY RANGE switch position. be obtained to permit use of this plug with two-
This control adjusts the amplitude of oscillator OUTPUT A TTENUA TORS
voltage applied to the output amplifier. The cali- These two attenuators are used to reduce the output
bration is in arbitrary units. level in one db steps to a maximum of llO db below
the output level indicated on the OUTPUT LEVEL
This switch selects the instrument output impedance.
The available impedances are 50,200,600, and
5000 ohms. 2-2 OSCILLATOR OPERATION
OUTPUT The procedure for operating the Model 205AGAudio
The instrument output appears at four terminals. Signal Generator is as follows:
The terminal marked CT is the center tap of the
line matching transformer. The-4-terminal is con- a. O:>nnect instrwnent ~wer cable to a ll5/230 V
nected to the chassis. The two vertically spaced alternating current power line and the output
terminals are connected to the line matching trans- terminals to the equipment being tested. Set the
former through the IMPEDANCE switch. A mlanced IMPEDANCE switch to match the load. When the
output is obtainedfrom the vertically slXtcedterminals Signal Generator is operated into a high impedance
Sect. li Page 2 Model 205AG
load, the Load Switch must be turned on, otllerwise For example: with an Output Level Meter indication
the Output Level M!ter and the Attenuator indications of 40 volts and the output attenuators set at 40 db,
will not be correct. The Load Switch shoul,dbe oH we find from Figure 2-1 that the true output voltage
when the instrument is connected to loads within into 600 ohms would be 40 volts multiplied by 0. 01
the range of the line matching impedance!), or 0.4 volts. To convert this to a voltage across
a 200 ohm matched load multiply by 0. 577 or 0. 4 x
b. Turn the power switch to ON and allow ~pproxi- 0. 577 = 0.2308 volts.
mately five minutes for the instrument to stabi-
lize. Set the Freq. ~nge control and the frE~quency
dial so that their indications whenmultiplied together 2-4 INPUT LEVEL METER OPERATION
equal the desired frequency. For example: Fre-
quency dial indication 20, FREQUENCY RANGE The Input Level meter is an independent audio tre-
X100, 20x 100 = 2000 cycles/second. quencyvacuumtube voltmeter, suitable for monitor -
ing the output voltage of a device under test. The
c. Set the output at tenuators and the AMPLrrUDE meter is calibrated involtsanddbabove 1 milliwatt
in 600 ohms when the INPUT A TTENUA TOR (DB)
control to obtain the desired output level Dis-
switch is on zero.
tortion in the output will be minimized by I~eeping
the Output Level meter indication near maxim.umand
When making comparative measurements across a
reducing the output with the output attenuators. constant impedance the meter and INPUT A TTENU -
A TOR (DE) switch will indicate directly the change
in db in the circuit under test.
2-3 OUTPUT LEVEL METER OPERATION
The Output Level meter is calibrated directly in When using the Input Level meter to monitor a 600
output voltage and db above 1 milliwatt when the ohm circuit, the power level in db above 1 milli-
instrument is operating into a 600 ohm load and watt is equal to the meter indication plus the indi-
both output attenuators are set at zero. cation of the INPUT ATTENUATOR (DB) switch.
With any matched load (50, 200, 600, or 500(]lohms) When making power measurements in circuits with
the output power in db above or below 1 milliwatt impedances below 600 ohms, the absolute level in
is equal to the Output Level Meter indication less db above or below 1 milliwatt is equal to the level
the output attenuator settings. For examp,le: an indicated on the meter plus the INPUT A TTENU -
Output Level meter indication of + 35 db and a total A TOR (DB) switch indication plus a correction
output attenuation of 45 db will produce an output factor for the circuit impedance. Figure 2-2 gives
levelof -10 dbm into a matched load. correction factors for impedances between 1 and
Figure 2-1 is a chart of meter voltage multiplying
factors for any value of output attenuation. With The input voltage level for any range of the INPUT
the IM:PEDANCE switch set at 600 ohms and an in- A TTENUA TOR (DB) switch is the voltage indicated
ternal or external 600 ohm load, the output 1roltage by the Input Level meter multiplied by the factor
will be the Output Level meter voltage ind:ication indicated below for the particular range of the IN-
multiplied by a factor obtained from Figure 2-1 PUT ATTENUATOR (DB) switch in use.
opposite the total output attenuation. For e~a.mple :
with the output attenuators set for 40 db aU Output
Level meter indications should be multiplied by
.01 to obtain the true output voltage into a 600 ohm
To obta in the true output voltage into a 50, 200 or
5000ohm load the following factors must be ~Lpplied
to the true voltage across a 600 ohm matched load.
Laad Impedance 600 Ohm Voltage
Mode1205AG Sect. n Page 3
10 100 1000
Figure 2-2. Input 'Level Meter Correction Curve
Model 205AG Sect. rn Page 1
3-1 GENERAL oscillation substantially constant over a wide fre -
quency range. The negative feedback also keeps the
The Model 205AGAudio Signal Generator consists of operation of the system on the linear portion of the
an oscillator, an amplifier, output meter and atten- tube characteristic.
uator, line matching transformer, and a conventional
power supply (see Figure 3-1). The amplifier section consists of a voltage amplifier
tube directly coupled ta a phase inverter which drives
the push-pull output tubes. The tertiary winding on
The oscillator section (tubes VI and V2) is a re- the output transformer provides negative feedback
sistance-tuned type circuit. Basically, this oscil- for the amplifier .
lator is a two-stage resistance-coupled amplifier
which is caused ta oscillate by the use of a positive The output meter and attenuator section is made up
feedback network. This network is a frequency- of an average reading type voltmeter and two bridged
selective resistance -capacity combination which T-type attenuators. The attenuators and voltmeter
controls the frequency of oscillation. By using a are connected between the output transformer sec-
variabIe tuning capacitor for the capacity of the ondary and the primary of the line matching trans-
network, it is possible to tune the oscillator over former.
a wide 10:1 range; and by using a switching arrange-
ment to select different values of resistance for the A full-wave rectifier and a dc milliammeter cali-
network, several ranges are given ta the oscillator. brated in volts and decibels mak.e up the Output
Level meter. The line matching transformer is
Negative feedback is used in the oscillator section used to change the 500 ohms line impedance to 50,
in order to minimize distortion and to obtain a very 200, 600, or 5,000 ohms output
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