Agilent Technologies 205AG Service manual

Errata
Title & Document Type: 205AG Audio Signal Generator
Manual Part Number: N/A
Revision Date: N/A
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Model 205AG Specifications
SPECIFICATIONS
1
OUTPUT METER:
Calibrated in volts and dbm (0 dbm = 1 mw,
600 ohms). Full scale values 65 volts, 37dbm.
Reads on 600 ohm basis regardless of output
impedance selected.
FREQUENCY RANGE :
20 cps ta 20 kc in three decade bands:
Xl
XlO
XlOO
20 cps
200 cps
2 kc
200 cps
2 kc
20 kc
ta
ta
ta
Calibration covers approximately 270degrees
on 6 inch diameter main dial. OUTPUT ATTENUA TOR:
Provides 110 db in 1 db steps.
INPUT METER:
Calibrated in dbm (0 db = I mw1 600 ohms)
from -5 to + 8 dbm and in volts from 0 to 2 v
rms. Voltage accuracy is :!:5%of full scale.
CALmRATION ACCURACY:
Within %2%at normal ambient temperatures.
(Includes warm-up and changes due to aging
of tubes and components. )
INPUT ATTENUATOR:
Extends meter range to + 48 dbm and to 200 v
rms in 5 db steps. Accuracy +0. 1 db.
OUTPUT:
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.
FREQUENCY RESPONSE:
:1 db 20 cps to 20 kc at output levels up to
+ 30 dbm with output meter reading held at
+ 37db, :1. 5db 20 cps to 20 kc at output levels
above + 30 dbm with output meter reading held
at + 37 db (reference 1000 cps).
DIMENSIONS:
Cabinet Mount: 20-3/4 in. wide, 12-3/4 in.
high, 15-1/2 in. deep.
DISTORTION:
Less than 1% at frequencies above 30 cps.
INTERNAL IMPEDANCE:
Approximately 1/6 load impedance with zero
attenuator setting. Approaches loadimpedance
with attenuator settings of 20 db or more.
HUM LEVEL:
More than 60 db below the output voltage or
90 db below zero level (1 mw, 600 oluns),
whichever is the larger.
WEIGHT:
Cabinet Mount: 56 tbs, shippingweight 78lbs.
Rack Mount: 49 tbs, shippingweight 71lbs.
00090-2 iii

Model 205AG
Table of Contents,
List of Illustrations and Tables
TABLE OF CONTENTS
Section ~ ! Page
IV MAIN ENANCE. IV-1
4-1 C binet Removal IV -1
4-2 be Replacement IV -1
4-3 Distortion IV -1
4-4 Cfl.pacitor Drive Lubrication .IV -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
4-8 R placement of Lamp R11 ..IV -2
4-9 I termittent Output. IV -3
Page
1-1
1-1
1-1
Section
I GENERAL DESCRIPTION1-1 General.1-2 Inspection
11-1
ll-l
ll-l
11-2
ll-2
II OPERATING INSTRUCTIONS2-1 Controls and Terminals. ...
2-2 Oscillator Operation2-3 Output Level Meter Operation ..
2-4 Input Level Meter Operation. ..
vREP ~CEABLE P ARTS.5-1 I troduction.5-2 O de ring Information V-l
V-l
V-l
rn CIRcurr DESCRIPTION m-l
3-1 General. llI-1
LIST OF ILLUsTRATIONs
Number Page Number Title Page
Title
1-1 1-1 3-1 m-lModel 205AG Audio Signal Generator . Bloc k Diagram.
2-1 4-1 Top V~ew Cabinet Removed4-2 Botto~ View Cabinet Removed ..
4-3 Schematic Diagram.
IV-4
IV-5
IV-6
Output Voltage Correction Factors
when using Output Attenuators ...
Input Level Meter Correction Curve . n-o
n-3
2-2
LIST OF TABLES
Number TUle Page
4-1 IV-3
Troubleshooting Chart I. .
5-1 V-l
ReplaceableParts
00090-2
iv

Model ~O5AG Sect. II Page 1
~
2-1 CONTROLS AND TERMINAILS and an unbalanced output may be obtained by con-
necting the~terminal to oneof the output terminals
with the captive link providedPOWER ON
This switch ccntrcls the power suppliedtc the instru-
menttrom the powerline. OUTPUT LEVEL
This meter indicates the voltage at the output ter-
minals when the IMPEDANCE switch is set at 600,
output attenuators OOthat zero, andthe instrument
is loaded with the internalor an external 600 ohm
load. Under other oper~ting conditions the meter
may be used as a monitor to insure constant output
voltage.
LOAD ON
This switch is usedta cannectan intern11laadacrass
the OUTPUTterminals.
INPUT
These terminals are the input for the audio fre-
quency INPUT LEVEL vacuum tube voltmeter in
the instrument. INPur LEVEL
This meter measuresthe voltage appliedto the input
terminals and the range of the meter is controlled
by the INPUT ATTENUATOR (DB) range switch.
INPUT ATTENUATOR (DE)
This switch is the range switch for the INPUT LEVEL
meter and is calibrated in steps of 5 db from 0 to
40 db.
~
),FUSE
The fuseholder, located Dn the back of the chassis,
contains the power line fuse. Refer ta the Table
of Replaceable Parts for the correct fuse rating.
FREQUENCY RANGE
The position of this switch indicates the multiplying
factor to be used with the frequency dia! indication. Power Cable
The three conductor power cable is supplied with a
NEMA approved three-prong plug. The third con-
ductor provides a chassis ground. An adapter may
be obtained to permit use of this plug with two-
conductor receptacles.
FREQUENCY Dial
This dial is calibrated in cycles per second.TheoUt-
putfrequencyis the frequency dial indication multi-
plied by the FREQUENCY RANGE switch position.
AMPLrrUDE
This control adjusts the amplitude of oscillator
voltage applied to the output amplifier. The cali-
bration is in arbitrary units.
OUTPUT ATTENUATORS
These two attenuators are usedto reduce the output
level in one db steps to a maximum of llO db below
the output level indicated on the OUTPUT LEVEL
meter.
IMPEDANCE
This switch selects the instrument output impedance.
The available impedances are 50,200,600, and
5000 ohms. 2-2 OSCILLATOR OPERATION
The procedure for operating the Model 205AGAudio
Signal Generator is as follows:
OUTPUT
The instrument output appears at four terminals.
The terminal marked CT is the center tap of the
line matching transformer. The-4-terminal is con-
nected to the chassis. The two vertically spaced
terminals are connectedto the line matching trans-
former through the IMPEDANCEswitch. A mlanced
outputis obtainedfrom thevertically slXtcedterminals
a. O:>nnecttheinstrwnent ~wer cableto a ll5/230 V
alternating current power line and the output
terminals to the equipment being tested. Set the
IMPEDANCE switch to match the load. Whenthe
Signal Generator is operated into a high impedance
00090-2

Sect. li Page 2 Model 205AG
load, the Load Switch must be turned on, otllerwise
the OutputLevel M!ter andthe Attenuator indications
will not be correct. The Load Switch shoul,dbe oH
when the instrument is connected to loads within
the range of the line matching impedance!),
For example: with an OutputLevel Meter indication
of 40 volts and the output attenuators set at 40 db,
we find from Figure 2-1 that the true output voltage
into 600ohms would be 40 volts multiplied by 0. 01
or 0.4 volts. To convert this to a voltage across
a 200ohm matched load multiply by 0. 577or 0. 4 x
0. 577= 0.2308 volts.b. Turn the power switch to ONandallow ~pproxi-
mately five minutes for the instrument to stabi-
lize. Setthe Freq. ~nge control andthe frE~quency
dial sothat their indications whenmultiplied together
equal the desired frequency. For example: Fre-
quency dial indication 20, FREQUENCY RANGE
X100, 20x 100= 2000cycles/second.
2-4 INPUT LEVEL METER OPERATION
The Input Level meter is an independentaudio tre-
quencyvacuumtubevoltmeter, suitable for monitor -
ing the output voltage of a device under test. The
meter is calibrated involtsanddbabove 1 milliwatt
in 600ohms whenthe INPUT ATTENUATOR (DB)
switch is on zero.
c. Settheoutput attenuators and the AMPLrrUDE
control to obtain the desired outputlevel Dis-
tortion in the output will be minimized by I~eeping
the OutputLevel meter indication near maxim.umand
reducing the output with the output attenuators. When making comparative measurements across a
constant impedance the meter and INPUT ATTENU -
ATOR (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
output voltage and db above 1milliwatt when the
instrument is operating into a 600 ohm load and
both output attenuators are set at zero.
Whenusing the Input Level meter to monitor a 600
ohm circuit, the power level in db above 1 milli-
watt is equal to the meter indication plus the indi-
cation of the INPUT ATTENUATOR (DB) switch.
Whenmaking power measurements in circuits with
impedances below 600ohms, the absolute level in
db aboveor below 1 milliwatt is equal to the level
indicated onthe meter plus the INPUT ATTENU -
ATOR (DB) switch indication plus a correction
factor for the circuit impedance. Figure 2-2 gives
correction factors for impedances between 1 and
600ohms.
With any matchedload (50, 200, 600, or 500(]lohms)
the output power in db above or below 1milliwatt
is equal to the Output Level Meter indication less
the output attenuator settings. For examp,le: an
Output Level meter indication of +35db anda total
output attenuation of 45 db will produce an output
levelof -10 dbm into a matched load.
Figure 2-1 is a chart of meter voltage multiplying
factors for any value of output attenuation. With
the IM:PEDANCEswitch set at 600ohms andan in-
ternal or external 600ohm load, the output 1roltage
will be the Output Level meter voltage ind:ication
multiplied by a factor obtained from Figure 2-1
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 600ohm
load.
The input voltage level for any range of the INPUT
ATTENUATOR (DB) switch is thevoltage indicated
by the Input Level meter multiplied by the factor
indicated below for the particular range of the IN-
PUT ATTENUATOR (DB) switch in use.
To obtain the true output voltage into a 50, 200 or
5000ohm load the following factors must be~Lpplied
to the true voltage across a 600ohm matched load.
600 Ohm Voltage
Multiplying Faetor
Laad Impedance
50
200
5000
0.289
0.577
2.89
00090-2

Mode1205AG Sect. n Page 3
+30
~
CD
a
I
z
Q
1-
u
w
cc
cc
o +20
U
cc
w
1-
w
~
1-
:)
0..
z
-+10
10 100 1000
:} IMPEDANCE-OHMS
Figure 2-2. Input 'Level Meter Correction Curve
00090-2

Sect. rn Page 1
Model 205AG
~
3-1 oscillation substantially constant over a wide fre -
quency range. The negative feedback also keeps the
operation of the system on the linear portion of the
tube characteristic.
GENERAL
The Model 205AGAudio Signal Generator consists of
anoscillator, anamplifier, output meter andatten-
uator, line matchingtransformer, anda 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 output transformer provides negative feedback
for the amplifier .
The oscillator section (tubes VI and V2) is a re-
sistance-tuned type circuit. Basically, this oscil-
lator is a two-stage resistance-coupled amplifier
which is caused ta oscillate by the use of a positive
feedback network. This network is a frequency-
selective resistance -capacity combination which
controls the frequency of oscillation. By using a
variabIe tuning capacitor for the capacity of the
network, it is possible to tune the oscillator over
a wide 10:1range; and by using a switching arrange-
ment to select different values of resistance for the
network, several ranges are given ta the oscillator.
The output meter and attenuator section is madeup
of anaverage readingtype voltmeter andtwo bridged
T-type attenuators. The attenuators andvoltmeter
are connectedbetweenthe output transformer sec-
ondary andthe primary of the line matching trans-
former.
Negative feedback is used in the oscillator section
in order to minimize distortion andto obtain a very
high order of stability .The amountof negativefee'd-
back is determined by a resistance network, one
element of which is non-linear (the 3-watt lamp in
the cathodeof VI). This elementcontrols the amount
of feedback in accordance with the amplitude of OS-
cillation andconsequentlymaintains the amplitude of
A full-wave rectifier and a dc milliammeter cali-
brated in volts and decibels mak.eup the Output
Level meter. The line matching transformer is
used to changethe 500ohms line impedance to 50,
200, 600, or 5,000 ohms output ïmpedance.
The Model 205AGalsoincludesanInput Levelmeter
which is of the average respondingtype.The meter
consists of a two stage amplifierwith negativefeed-
back., a full-wave rectifier and a dc milliammeter
calibrated in volts anddecibels.
I LINEMATCHING
TRANS.
--0
-OOT 0-
-0G
-"OOTPUT ':
r-.- r-+-
~
-.- -.-
@
0--
IHPIJT
0--
G
Ra 115/230 V
Figure 3-1. Block Diagram Model 205AG
00090-2