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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.

                                                                   INPUT METER:
       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. )

                                                                   INPUT ATTENUATOR:
                                                                     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.

       HUM LEVEL:
         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.

    00090-2                                                                                                                         iii
Table of Contents,                                                                                                                                          Model    205AG

List of Illustrations and Tables

                                                                     TABLE               OF        CONTENTS
                                                                                                                    ~ !                                                Page
Section                                                                             Page              Section
I         1-1
          1-2     General.
          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
          2-3       Output
                    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

                                                                                                      v      REP
                                                                                                             5-2     O
                                                                                                                    ~I      CEABLE
                                                                                                                           de    ring           P
                                                                                                                                         InformationARTS.               V-l
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
                                                                                                             Top             Cabinet
                                                                                                                                  Cabinet Removed
                                                                                                                                              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

    iv                                                                                                                                                              00090-2
     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.
                                                              Power Cable
     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-
                                                              conductor receptacles.
     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
     IMPEDANCE                                                meter.
     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.
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
                                                         600 ohms.
 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
                            Multiplying Faetor

             50                   0.289

           200                    0.577

           5000                   2.89

     Mode1205AG                                                     Sect.   n   Page   3

     o      +20




                            10                            100                     1000

:}                               IMPEDANCE-OHMS

                  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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