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

Model 205AG Sect. IV Page 1
~
";
ic"
4-1 CABINET REMOV AL NOTE
Removefour screwsfrom the rear of the cabinet and
remove the rear cover. Place instrument on its
back, andloosenthetwo screws locatedonthe under-
side of the front ~nel bezel. Free cabinet and lift
from instrument.
For all adjustments the output must be loaded with
the internalload. Turn the LOAD switch ON.
The frequency calibration will be correct only when
the shields around and abovethe main tuning capa-
citor are firmly in place.
Using a gentIe airstream, blowout any dust that
may be present on the tuning capacitor .
4-2 TUBE REPLACEMENT
The tubes in this instrument may be replaced with
anytubehavingEIA standardcharacteristics. When-
ever a tube is replaced, with the exc.eptionof V7
or VB, the distortion should be measuredto seethat
it does not exceedthe specifications. Whentubes
V7 or VBare replaced it may benecessary to adjust
the zero setting of their respective meters.
a. Checkfor proper setting of diaIon shaft. At one
endof the frequency dia! will be either a small
dot or an extra line. This should be under the in-
dicator hairline whenthe tuning capacitor is at that
endof its travel. This may beadjustedby loosening
set screws on one side of the coupIer behind the
panel, then rotating the dial until correctly lined up.
Check and tighten al! set screws in the dial drive
mechanism.
4-3 DISTOlTION
Excessive distortion may be caused by detective
tubes, open by-pass capacitors, and low voltages. b. Turn on the instrument and allowat least 30
minutes lor it to warm up.
4-4 CAPACITOR DRIVE LUBRICATION
The capacitor drive should be luhricated once a year .
Remove the cover plate from the top of the capacitor
shield. Put one drop of light oil on each of the bear-
ings on the sma11gear shaft at the top of the drive.
The capacitor 00.11hearings do not need luhrication.
c. Setto X10range and dial to 20. Setthe output
meter to 50volts. Changedia! setting to 200.
The paneloutput meter should then read 50 volts
%2volts and the frequency should be 2000cps %2%.
H OOthfrequency and amplitude are in error, adjust
Cl andC22for thebestcompromise betweencorrect
frequencyand correct amplitude.
d. Check tracking of the rest of the frequency djal.
If there is no constant error in tracking, pro-
ceed with the next step. If there is a constant error ,
proceed with one of the following methods, which-
ever is the easiest.
4-5 FREQUENCY CALIBRATION ADJIUSTMENT
The range switch resistors Hl to H6 inclusive in
conjunction with tre tuning capacitor assembly Cl and
C2. determine the frequency of the oscillation of the
unit and also aifect the amplitude. If the output fre-
quency is not within 2% of that indicated by the dial.
or li the amplitude varies more than :!:1/2 db from
200 to 2000 cps. the following procedure is recom-
mended.
1. Loosen set screws and reset the dial to take the
error into account, then repeat steps b andc. Tbis
metbod is best tl the other ranges also have a con-
stant error in the same direction.
00090-2

Sect. IV Page 2 Model 205AG
2. Changethe srnal1paddingresistors in series with
theprecision resistor onthe range switch. :[ncreas-
ing the va1ueof the resistor by 10,000 ohms wi11
1owerthe frequency of the range approx~Lte1y 1%;
decreasing the va1ueof this resistor wi11raise the
frequency of the range.* Hetrace steps a through d.
4-7 INPUT LEVEL METER ADJUSTMENT
(
This meter is adjustedasfollows:
a. With the instrument operating, short circuit
the Input Terminals. Adjust the meter pointer
to zero with zero adjustment screw on the meter .
Whenthe XlOrange bas beenproperly a.djusted,
the other ranges may be adjusted as :follows:
e. b. Connectthe input terminals to the Output ter-
minals andset the instrument controls as follows:
1. X100range
Changethe paddingresistor in series with 1:hepre-
cision resistor. A changeof 1000ohms wil:Lchange
the frequency approximately 1%on this range. Then
20,000 cycles on the dial is corrected by varying
C-7. A changeof 50ta 200 pf is usuallyaldequate.
2. XI range
An increase of IOOKohms in the padding resistor
will decrease frequency approximately 1%on this
range. There may be a small tracking error (less
than 2%)at the top or the bottom of the X;l range.
This is normal to the instrument and cannot be
eliminated.
f. If satisfactory calibration cannot be obtained
in the above manner, it may be neceslsary ta
return the instrument to an authorized re~ir station
or the factory . The Input Level meter should indicate zero db with
the controls set as above. Jf the meter indication
is incorrect, ac;ijustthe variabIe resistor R417to
correct the meter indication. The variabIe resistor
R47is reachedthrough a hole in the left side of the
chassis. (Instrument removed from cabinet. }
4-6 OUTPUT LEVEL METER ADJUSTMENT
The procedure for adjusting the Output Level meter
is as follows: c. After the zero db level is in adjustment, change
the attenuatars ta 4l db and 5l db which will in-
dicate + 5 db and -5 db respectively; If the m~ter
tracking at these points is nat satisfactory, then the
6B9-tu~-sllg.\1ld-re...r.ep]a ced,-and,"the.-a.00.v.e..adj.ust-
ments..r.epeated.
a. With the instrument operating andVol. control
at zero, adjust the meter pointer to ze~rowith
zero adjustment screw on the meter.
b. Connect an accurate vacuum tube voJltmeter
across the 600 ohms output terminals 11liththe
600 ohms internalload switched on. Set the in-
strument for 100cycles/sec. output, zero atten-
uation, andadjust the Vol. control until the external
voltmeter indicates 55 volts. Adjust the variabIe
resistor R29until the Output Level meter iTJIdicates
exactly 55volts. The resistor R29, which is reached
through a hole in the back of the chassis, can be
turned with a screwdriver .
4-8 REPLACEMENT OF LAMP R11
The 3-watt lamp RU is operated at a very low level
and shouldhavean almost infinite life. Therefore,
the lamp should not be changed indiscriminately.
However, should the lamp require changing, it is
necessaryto measurethe ac voltagefrom the junction
of R58 and C4 to the chassis with the new lamp in
the circuit. This voltage should bemeasured with a
high impedance vacuum tube voltmeter such as
Hewlett-Packard Models 400C, 400D, or 4l0B.
* Up to 1% change in frequency on any ran~e may
be made by adjusting only one of the two range
re sistor padders on that range. If a greatler fre-
quency change is needed, adjust both padders.
If this is not done, the relative amplitude b,etween
ranges will be affected. Ta make this measurement andadjustment, the in-
strument must be remaved fram the cabinet. Set
00090-2

Model 205AG Sect. IV Page 3
the oscillator frequencyto 1000cycles/sec. andvary
the resistor Rl9 sothat 21to 25volts is ol:tained. The
resistor R19is mounted on the shield surrounding
~e Freq. RangeSwitch.
ing of the 3-watt oscillator lamp (RIl) is a reliable
indication of a short in trimmer capacitor Cl or in
the first two sections of the main tuning capacitor .
If these symptoms occur, search out and clear the
short with a weak air jet or other means. Do not
bend the capacitor plates because bending capacitor
plates will destroy the frequency calibration.
1! the voltage cannot be brought within the 21 to 25
volts range by means of R19, the new lamp should
be rejected in favor of another.
A short in the back two sections of the main tuning
capacitor will prevent the circuit from oscillating.
Any such short should be cleared as explained
above.
4-9 INTERMITTENT OUTPUT
"Jumpy" or intermittent output accompanied by fIash-
TABLE 4-1. TROUBLESHOOTING CHART
The following if; a listing of possible symptoms, causesand remedies
SYMPTOMS CAUSES REMEDIES
Instrwnent inoperative
(Indicator lamp won't
light, no audio output)
Blown fuse. Clear short circuit
and replace fuse .
Instrument inoperative
(Indicator lamp lightsl
no audio output)
Replace tube.
Detective tube.
Check the 5U4GA/B
tube tirst,
Short circuit in DC
power circuit capacitor. Replace capacitor .
Short circuit in C2
(two rear sections) Clear the short circuit
as outlined in Pa.ragraph
4-9.
Intermittent output Capacitors C3, C4,
C5, ca or C9
intermittently open.
Replace capacitor .
Short circuit in C2
(two front sections)
or CL
Clear the short circuit
as outlined in Paragraph
4-9".
Output Level Meter
inoperative. 6H6 tube V7 detective. Replace tube .
Excessive distortion. Defective tube. Replace tube.
Opencircuit in
capacitor CIOabc,
C15, C16, C17, or
C18.
Replace capacitor.
Defective output or
line matching trans-
former
Replace transfarmer .
00090-2

Model 205AG
lJII,"l",Ii","J'..lidi'"~"Uic~""",ji d,".
Sect. IV Page 5
I
, 1

MODEL 205AG
AUDIO SIGNAL GENERATOR
Manual Serial Prefixed: 012-
Manual Printed 5/61
To adaptthis manual to instruments with other serial prefix es checkfor errata below, andmake
changesshownin tables.
Instrument Serial Prefix Instrument Serial Prefix Make Manual Changes
Make Manual Changes
6
All
CHANGE #1 'v Paragraph 4- 7, step b,
Change the setting of LOAD switch to 9!.!' .
vParagraph 4-7, line #5 of step c,
Change to read: "diodes CRI, CR2, CR3, and CR4 should be replaced
and the above adjustments repeated. "
The 205AGcontains two terminal boards onwhich are mounteda variet y of
small parts. The boards used in earlier instruments (24-terminal board
StockNo. 2G-75A; 14-terminal board StockNo. 2G-75B) utilized solder
lugs to mountparts. The boards used in later issue instruments, having
serial prefix number 151-(large board StockNo. 2G-75C; small board
StockNo. 2G-75D)are directly interchangeable, andthe etched-circuit
board will be supplied as a replacement part for both types.
CHANGE #2
CHANGE #3 vFigure 4-3,
Change V3 ta read, "6SQ7".
CHANGE #4 Table of Replaceable Parts
1/ Was C19, Capacitor -fixed, 20 Jlfd, 50 vdc
Mfr. , 37942, ~ Stock No.0180-0026, TQ-1, RS-1.
Now C19, Capacitor -fixed, 20 j:Lfd, 50 vdc
-Mfr. , 56289, (6j!Stock No.0180-0049, TQ-1, RS-1.
v
CHANGE #5 Table of ReplaceableParts
Delete the following:
Spring, Gompression, StockNo.1460-0019, 1 ea
Vernier Disc, StockNo. G-14A, 1 ea
Vernier Disc, StockNo. G-14B, 1 ea
Add the following:
Disc Ass'y Vernier Drive, Stock No. G-14J, Mfr. 28480, TQ-l
Bearing Capacitor Drive, Stock No. G-36J, Mfr. 28480, TQ-l
Spring Thrust, Stock No. G-91A, Mfr. 28480, TQ-l
CHANGE #6 "Table of Replaceable Parts
Was Attenuator, output, complete ltJ!)Stock No. 2AG-34
Now Attenuator, output, complete ltJ!)Stock No. 2AG-34A
8/13/62 (9-1117)

MODEL 2O5AG
AUDIO SIGNAL GENERATOR
Manu.:l1 Seria1 Prefixed: 012-
Manua1 Printed: 5/61
Ta adaptthis manualta instruments with ather serial prefix es checkfar errata below, and make
changesshawnin tables.
Instrument Serial Number Make Manual Changes
Instrument Serial Number Make Manual Changes
13.4.5.,6
5667 to 6236
1, 3, 4, 5, 6, 7
4688 ta 5666
I Below 4688
CHANGE 1
R29: Change to 500 ohms, ~Stock No. 2100-0011.
R53: Change to 22K ~pms, ~Stock No.0690-2231.
Add R54: 22K ohms, ~Stock No.0690-2231.
R62,63: De1ete
CR1 to CR6: Delete
Add V7, 9: Type 6H6 tubes.
Add R59: 7 ohm resistor, connected in series with V9, heat er pin 7.
Change to 27.5K ohms, ~Stock No.0730-0048.
R30:
CHANGE 2
11: Change to GE-47 lamp, ~Stock No.2140-0009.
Add R56: 33 o9~s resistor in series with 11.
Lens: Change q;, Stock, No. to 1450-0026.
Lampholder: Change (hpStock No. 1450-0027.
Clli\NGE 3
CIIANGE C19:
H61: Change to 1000 pf.
Chan~e to 100 ohms.
4
6/8/62- UD (over)

?tlanual Changes Model 20SAG Page 2
Make Manual ChangesInstrument Serial Number Make Manual Changes Instrument Serial Number
8312 to 8462 5667 to 6236
1, 2 I, 3, 4, 5, 6
7712 to 8311 1,213
1,2,3; 4
4688 to 5666 1,3,4
8
5, 6, 7
Below 46887612 to 7711
6237 to 7611 1, 3, 4, 5
CHANGE 5H30: Change value to 25.2K ohms.
C19: Change to 1000 pf.
H4: Change to 82,500 ohms.
H5: Change to 825K ohms.
H6: Change to 8.35 M.
Add H7: 5000 ohm potentiometer between H4 and ground.
Add H8: 50Kohmpotentiometer between H5 and ground.
Add H9: 500K ohm potentiometer between H6 and ground. ,
R24: Change to 1.2M.
H58: Change to 39K ohms.
H61: Delete
SI: Change 1tIp Stock l~o. to 2AG-19W.
The range switch resistors Hl to H6 inclusive and the individual range
adjustment potentiometers H7 to H9 inclusive in conjunction with the
tuning capacitor asse111bly Cl and C2, determine the frequency of the
oscillation of the unit and also affect the amplitude. If the
output frequency is not within 2% of that indicated by the dial, or if
the amplitude varies more tl;an z.1/2 db from 200 to 2000 cps, the
following procedure is recommended:
IAIPORTANT
For all adjustments the output must be loaded with the internal load.
Turn panel load Switch ON,. Toe panel meter is used tor voltage
measurements in this procedure.
The frequency calibration will be correct only when the shields
around and above the main tuning capacitor are tirmly in place.
Blowout any dust that may be present on the tuning capacitor.
Use a gentIe air st~!~~~I) Check for proper setting of diaIon shatt. At one end of the
trequency dial will be either a small dot or an extra line. This
should be under the indicator hairl1ne when the tuning capacitor is
at that end of its travel. This may be adjusted by loosening set
screws on one side of the coupIer behind the panel, then rotating
the dial until correctly lined up.
Check and tighten all set screws in the dial drive mechanism.
2) Turn on instrument and allowat least 30 minutes tor it to
warnl up .
3) Set to XIO range and dial to 20. Set the XIO adjustment
potentiometer R8 so that the frequency is exactly 200 cps. Set
the output meter to 50 volts. Change dial setting to 200. The
paneloutput meter should then re ad 50 volts + 2 volts and the
frequency anu amplitude are in error, adjust ~l for the best
compromise between correct trequency and correct anlplitude.
6/8/62- UD

Manual Changes Model 205AG Page 3
Instrument Serial Number Make Manual Changes Instrument Serial Nurnber Make Manual Changes
CHANGE 5 (cont.) If instrument does not have control RB, set dial to 20. To correct
error in frequency and amplitude, adjust trimmer Cl for best
compromise of frequency and amplitude. If instrument also has
trimmer C22, adjust Cl and C22 alternately so frequency is 2000
cps and amplitude is 50 volts.
4) Check tracking of the rest of the f'requency dial. Ir there
is no constant error in tracking, proceed with the next step. Ir
there is a constant error, proceed with one of the following methods
a, b, or c, 'whichever is the easiest .
a. Loos,en the set screws and reset the dial to take the
error iffto account, then repeat steps 2 and :3. This method
is best ir the other ranges also have a constant error in
the same direction.
b. Chanl~e the setting of range switch adjustment RB. Ir a
greater I::hange is necessary than can be obtained by changing
the potentiometer RB, change the small padding resistors in
series w:ith the precision resistor on the range switch.
Increasing the value of the resistor by 10,000 ohms will lower
the rrequency of the range approximately 1%; decreasing the
value of this resistor will raise the rrequency of the range.*
Retrace steps 1 through 4.
c. Ir Oll the XlO range there is Dot more than 1% or 2% error
in tracking across the dial, this may be corrected by bending
the split rotor plates on the tuning capacitor C2.
Reset dial for best tracking to lowest possible dial point,
then adjust calibration of' the dial points which do not track
by bending outer rotor plates of the tuning capacitor.
At tempt 1;0 bend the plates in each section by the same amount.
When bending capacitor plates, it is necessary to remove the
top shield to bend the plates and then to replace it af ter
each bending operation. The instrument changes frequency
when the shield is removed.
5) When the XlO range bas been properly adjusted, the other
ranges may be adjusted as rollows:
a. XlOO range. Adjust potentiometer R-7 to make 2000 cycles
on the dial read correctly. Ir this potentiometer does not
give sufficient range, it may be necessary to change the
padding resistor in series with the precision resistor. A
change of 1000 ohms will change the frequency approximately
1% in this range.
618162- BD (over)