POTOMAC INSTRUMENTS INC. AG-51 User manual

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INSTRUCTION MANUAL
AUDIO GENERATOR
Model AG-51
POTOMAC INSTRUMENTS, INC.
932 PHILADELPHIA AVE.
PI
SILVER SPRING, MD. 20910

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WARNING
This i nstru rnent rnust be used with a 3 prong U
grounded receptacle outlet. Failure to use a
grounded outlet rnay result in improper opera
tion or safety hazard.
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AUDIO
GENERATOR
MODELAG-51
INSTRUCTION MANUAL
POTOMAC INSTRUMENTS INC.
·
932
Philadelphia Avenue
Silver Spring, Maryland
20910
(301)
589
-
2662
Rev
i
ed
1 February
1979

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WARRANTY
FOR EQUIPMENT
AND
ACCESSORIES
Potomac Instruments Inc. warrants each new equipment
to
be free
of
defects in material
and workmanship,
for
a period
of
one (
1)
year after date
of
original shipment, except
for
fuses, transistors, diodes, and integrated circuits,
which
are warranted
for
a period
of
ninety
(90) days.
Any
instrument
which
is
found
within
one year
not
to
meet
the
fore-
going standards
after
examination
by
our
factory,
will
be
repaired
or
at
the
option
of
Potomac Instruments replaced
without
charge. This warranty does
not
apply
to
equip-
ment
which
has
been altered,
improperly
handled,
or
damaged in any way.
CHANGES IN SPECIFICATIONS
The
right
is
reserved
to
change
the
published specifications
of
equipment
at
any time, and
to
furnish merchandise in accordance
with
current
specifications,
without
incurring any
liability
to
modify
equipmentpreviously sold.
RETURNING
EQUIPMENT
TO
THE
FACTORY
Factory service is available
for
repair and adjustment
of
this
instrument; however, a
des-
cription
of
the
troub
le, plus
the
model and serial number(s)
of
the
unit
should be
for-
warded first, whereupon instructions
for
correcting
the
troub
le
or
authorization
for
returning the equipment
will
be given. This applies
to
all units, whether under warranty
or
not.
Shipment
in
an
improper
container may result
in
damaged equipment thereby
voiding warranty.

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TAB LE OF CONTENTS
Paragraph Title
Page
SECTION 1 GENERAL
DESCRIPTION
l.l
Function
1-1
1.2 Electrical Characteristi
cs
1-1
1.3 Specifications
1- 1
SECTION 2
OPERATING INSTRUCTIONS
2.1
lnstallation
2-1
2.2 Controls and Indicators 2
-1
2.3 Connectors 2-4
2.4
Fuse Location 2-4
2.5 Operating Procedures 2-4
2.5.l
Tum - On Procedure 2-4
2.5.2
Output Mode Selection 2-5
2.6
Application Not es 2-5
2.6.l
Distortion Measurements 2-5
2.6.2
Output Circuit and Termination 2-5
2.6.3 StereoTests 2
-6
2. 6.4
Equipment Performance Measurements 2-6
2.6.5 Grounding 2-6
SECTION 3
TH EORY OF OPERATION
3.1 Overall Description
3-1
3.2
Detailed Theory of Operation
3-1
3.2.1 Variable Frequency
Wien Bridge Oscillator
3-1
3.2.2 Fixed Frequency Wien Bridge Oscillators 3-3
3.2.3 Power Amplifier 3-3
3.2.4
Output Monitor 3-3
3.2.5
Output Attenuator Switching 3-3
3.2.6
Output Mode Switching 3-3
3.2.7 Test/Operate Switching 3-4
3.2.8 Regulated Power Supply 3-4
SECTION 4
MAINTENANCE
4.1 General
4-1
4.2 Periodic Maintenance
4-1
4.3 Alignment Procedure/Performance Test
4-1
4.3.1 Power Supply
4-1
4. 3.2
Oscillator Pre-Amplifier, A6
4-1
4.3.3
Control Amplifier Board, A7 4-2
4.3.4
Output Monitor, Buffer Amplifier, AS
4-3
4.3.5 IM/WF Signal Generator,
A4
4-3
4.3.6
AG-5J Overall Performance Test 4-4
4.4
Troubleshooting,General 4-5
4.5 Circuit Module Troubleshooting 4-6
4.5.1 General 4-6
4.5.2
Power Supply Al
4-6
4.5.3 Power Amplifier/Inverter A2, A3 4-6
4.5.4 IM/WF Generator,
A4
4-6
4.5.5 Buffer Monitor,
AS
4-9
4.5.6
Oscillator Preamp, A6 and Control Amp, A7 4-9

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LIST
OF
TABLES
Table Title
Page
4.1 AG-51 Performance Test
4.4
4.2
Voltage Readings,Power
Amp
/Invert
er
A2
and
A3 4.9
4.3 Voltage Readings, IM/
WF
Generator,
A4
4-10
4.4
Voltage Readings,
Output
Mo
nitor
/
Attenuat
or
Buffer,
AS
4-10
4.5
Voltage Readings, Wien Brid
ge
Oscillator
Pr
e Amp, A6 4-10
4.6
Voltage Readings,
Control
Amp, A7
4-11
4.7
Voltage Readings, Po
wer
Supply AJ
4-11
4.8
Parts
Li
st, AG-51 Chassis 4-29
4.9
Parts List, Power Supply PCB Assembly,
Al
4-30
4.10
Parts List, Po
wer
Amp
/
invert
er
PCB Assembly, A2, A3
4-
31
4.11
Part
s List, fM/WF Signal G
enerator
PCB Assembly,
A4
4-32
4.12
Parts List,
Ou
tp
ut M
on
itor
/B
uffer Amp PCB Assembly,
AS
4.33
4.13
Parts List, Oscillator Pre-Amp PCB Assembly, A6
4.34
4.14
Parts List, Control
Amp
PCB Assembly 4-35/4-36
LIST
OF
ILLUSTRATIONS
Figure
Title
Page
2.1 AG-5 l Controls
and
Indicators 2-2
3.1
AG
-51
Block Diagram 3-2
4.1
Troubleshooting Chart,
Outpu
t Leve
l/
Distorti
on
4-7
4.2
Generator
Frequency
Troubleshooting Chart 4-8
4.3
Circuit Module and
Test
Point Location, AG
-S
I 4-12
4.4
Switch
Configurations 4-13
4.5
Component
Location, Power Supply,
Al
4-14
4.6
Schematic Diagram, PowerSupply,
Al
4-15
4.7
Component
Location, Power Amp/Inverter,
A2,
A3 4-16
4.8
Schematic Diagram, Power
Amp/
lnverter, A
2,
A3 4-17
4.9
Component
Lo
cation,
IM/WF Siganl Generator,
A4
4-18
4.10
Schematic Diagram,
IM
/WF Signal G
ener
ator
,
A4
4-19
4.
I I
Component
Location,
Oulput
Monito
r/
Buffer
, AS 4-20
4.12
Schematic Diagram,
Output
Monito
r/
Buffer, A5 4-21
4.13
Component
Location, Oscillator
Pr
e-Amp, A6
4-22
4.14
Schematic Diagram, OscillatorPre-amp, A6 4-
23
4.15
Component Locati
on,
Control
Amp
, A7 4-24
4
.1
6
Schematic Diagram,
Control
Amp, A7
4-25
/
4-26
4.17
Wiring Diagram, AG-51 4-27/4-28
11

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1.1 FUNCTION
SECTION 1
GENERAL DESCRIPTION
Th e Model AG-5 l Audio Generator furnishes audio signa ls from +20 dBm to - 79.9 dBm* over
the frequency range of 20 Hz to 200 kHz to a 600-ohm load. At a 150 - ohm load, the audio signal levels
are O dBm to - 99.9 dBm. The maximum output level is monitored and can be verified by a built-in test.
1.2 ELECTRICAL CHARACTERJSTICS
The Model AG-5 I generates l ow distortion sine wave signals from 20 Hz to 200 kHz in four
decade ranges. Frequency of the output signal is indicated by a calibrated dial and a range multiplier.
Calibration accuracy is
better than ±3% . It also generates an intermodulation distortion test signal of
60 Hz and 7 kHz mixed in a 4: l ratio. Additionally, it generates a fixed sine wave frequency of 3.15 kHz
for use in wow and flutter measurement. The output attenuator is calibrated in 10, I and 0.1 decibel
steps. When
the AG-5 l is connected to a 600-ohm resistive load, the maximum power output is +20 dBm*
which
may be verified by the buj\t-in test feature.
Separate left and right channel outputs are provided, with switch-selected in-phase, inverse-
phase, left-only
and right-only output signals to facilitate a variety of stereo broadcast system performance
measurements.
1.3 SPECIFICATIONS
Frequency Rang e:
Outputs:
Output Impedanc e:
Unbalanced:
Fully balanced:
Output Level:
Sine Wave Signals:
IM Signal:
Output Level Accuracy:
20 Hz to 200 kHz in four decade ranges.
LEFT only, RIGHT only, LEFT and RIGHT in phase (L&R), or
LEFT and RIGHT 180° out of phase (L-R); switch selected
IM composite
60 Hz and 7 kHz@ 4: 1 ratio (SMPTE standard)
3. 15 kHz fixed wow & flutter signal (IEEE Standard 193-1971)
150
ohms or 600 ohms; switch selected
150 ohms or 600 ohms; switch selected
(No
Attenuation)
+20 dBm* (7. 75V) across 600 ohm load, 15.SV open circuit
0 dBm (.387V) across 150 ohm load, 0.774V open circuit
P
ea k-to - peak voltage of composite waveform is equal to peak-to-
peak voltage of +20 dBm sine wave across 600 ohm load, 0 dB
sine wave across 150
ohm load.
20 Hz - 100 kHz, ±0.2 dB
100 kHz - 200 kHz , ±0.5 dB
*Units
with serial numbers 133 and below have a maximum output le ve l of+ 18 dBm (6.15V RMS) and
and minimum output level of -81.9 dBm.
1-1

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1.3
SPECIFICATIONS
(Cont.)
Attenuator
Range:
Attenuator
Accuracy:
0
to
10
dB:
>
10
dB:
Intrinsi
c
Distortion*
:
Harm
on
ic
50
Hz
to
7.5
kHz
20
ll
z
to
20
kHz
I
ntermodulation
Incide
ntal
FM
(3.15
kHz)
Hum
and
Noise:
Dial
Accuracy:
External
Pow
er:
Dimensions
with
cover,
cm
(in):
Rack
mount
space
with
rack
mount
option
Weight
with
cover, kg Obs):
0
to
99.9
dB
in
0.1 dB
steps
±
1.5%
of
attenuation
in
dB
±0
.2
dB
(max.)
Low
Distortion
<
.05
%
<
.08%
<
.0
3%
<
0.01
%
>
80
dB
below
rated
output
±3%
Fast
Response
< 1%
< 2%
117 VAC,
(230
V
AC
option)
50
or
60
H
z,
9
Watts
38
.
74
(15-1/4)
wide,
13.34
(5-1
/4)
high,
25
.75
(10-1/8)
deep
5¼
inches
5.44
(I
2)
*Slightly
higher
at
R
output
in
L-R,
UNBAL
mode
.
1-
2

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2.1 INSTALLATION
SECTION 2
OPERATING INSTRUCTIONS
The Model AG- 51 is ready for operation as delivered, and need only be connected to an AC
power source.
WARNING
The AG-51 must be used with a 3-prong U-grounded
receptacle outlet. Failure to use a grounded
outlet
may result in improper operation or safety hazard.
2.2 CONTROLS AND INDICATORS
The following controls and indicators are identified on Figure 2-1.
2.2.1 POWER Switch (SI)
Applies AC power to the unit when in the ON position.
2.2.2 POWER Indicator (DSl)
Illuminates to indic ate the presence of main DC (+30V) power.
2.2.3 FREQ Range Switch (S2)
In the XI , XI 0, X100 and XI 000 positions, S2 selects the variable frequency output . The
setting of this switch indicates the multiplier for the calibrat ed FREQ dial (Cl).
In the IM SIG position, S2 selects the special IM distortion test signal (60 Hz+ 7 kHz) output.
The FREQ dial (C 1) has no effect when S2 is in this position.
In the 3.15 kHz position, S2 selects the 3.15 kHz wow and flutter test signal. This signal is
afixed frequency; thus, the FREQ dial wiJI have no effect when this position is selected.
2.2.4 FREQ Dial (Cl)
This calibrated dial may be used to set the desired output frequency with an accuracy of ±3 %,
when the FREQ Range Switch is in the Xl , XIO, XlOO or XlOOO position. The output frequency in
Hertz equals
the dial setting multiplied by the switch setting.
2- 1

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S2
XI
LOWOIST
---
-
FRCOI----
3JS
....
FAST
RCSPONSE
..
°"
[!]
C1
S7
8AI.
UNBAL
Lt:.J
S3
/
·•'f'\,.__,_..,..
_____
_jli
____
,
.,...
___
,_
__
~
001
~
I..
Fl
AlJfllO
IA.N~HA!llof
!'l'l'I
AC
•,1
'.'J!ll.Al-
1'0
Af
~I
'SV!>HIJI
KHOM-'C
INSTmJ.l,U
MIS,
I~
--"l\'I.R~~
lilll
•HVA.'..
11,o\
J9
S6
OS2
S4
FRONT
PANEL
AC
OUT
REAR PANEL
S8
Figure 2.1. AG-51 Controls a
nd
Indicators
2-2
S10
S9
l
OUT
ROUT
+2008M
MAX
• '
J7
JS
GROUND

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2.2.S LOW DIST/FAST RESPONSE Switch (S3)
In the FAST RESPONSE position, this switch selects a shorter time constant for the automatic
gain control circuits associated with the variable frequency oscillator. This position provides fast correction
of amplitude as the frequency is varied, but causes higher distortion.
The LOW DIST setting of S3 will insure the lowest distortion throughout the frequency range
of the AG-51, but will allow some momentary change in output amplitude if the frequency is changed
rapidly.
2.2.6 TEST/OPERATE Switch (S4)
The TEST/OPERATE Switch may be placed in the TEST position to activate a test of the
basic output signal level. Indicator DS2 will illuminate if the signal level is correct within ±0.5 dB. This
test may be used with any setting of the FREQ Range Switch or FREQ dial.
When
S4 is in the TEST position , the output levels go to zero while th e correct impedance is
maintained.
Thus , S4 can be used to remove and reapply a test signal.
2.2. 7 TEST Indicator (DS2)
This indicator is used in conjunction with the TEST/OPERA TE Switch and illuminates to
indicate correct generator output signal level (±0.5 dB).
2.2.8 BAL/UNBAL Switch (SS)
The BAL/UNBAL Switch is used to select either balanced or unbalanced configurations of the
generator outputs at the LOUT and ROUT connectors. With S5 in the BAL pos ition, an output signal
will
be supplied across pins 1 and 3 of each jack, balanced with respect to ground. The connector shell
is grounded
to the chassis. When S5 is in the UNBAL position , the output signal is supplied on pin 3 of
each jack , with pin 1 at chassis ground . In both positions the same voltage exists between pins 1 and 3.
2.2 .9 OHMS Switch (S6)
S6 is used to select either 600 Ohm or 150 Ohm output impedance. When the 600 Ohm
impedance is selected, t he generator output into a 600 ohm load (zero attenuat i on) will be +20 dBm*
for all frequencies. Generator output with S6 in the 150 Ohm position is OdBm into a 150 ohm load
(zero attenuation). ·
2.2.10 OUTPUT Se1ect Switch (S7)
This switch selects the following output configurati ons at J7 (LOUT) and J8 (ROUT):
a. L pos ition -provides generator output at J7 or left channel only; (ROUT) output is
zero at the correct impedance.
b. R position -provides ge
nerator output at J8 or right channel only; (LOUT) output is
zero
at the correct impedance.
*+ 18 dBm for serial numbers 133 and below.
2-3

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2.2.11
c.
L+R
position
-provides in-phase
output
signals
on
both
channels.
d.
L-R
position
-provides signals
of
opposite phase
(180°
out)
on
right
and
left
channe
ls;
the
L
signal is unchanged, while
the
R
signal is reversed
in
phase.
ATTENUATOR
Switches:
-10
dB
Steps
(S8),
1
dB
Steps
(S10);
0.1
dB
Steps
(S9):
When the
150
Ohm
output
impedance is selected (S6), genera
tor
output
level
may
be
set
directly
in
-dBm
by
using
SB
for
the
tens
digit,
S10
for
the
ones digit,
and
S9 for
tenths.
If
the
600
Ohm
output
impedance is being used, the
ATTENUATOR
settings
show
the
amount
of
attenuation,
in
dB,
being applied
to
t
he
basic
output
level
of
+20
dBm. Thus,
for
an
output
of
+2
dBm
at
600
Ohms
im-
pedance,
the
ATTENUATOR
Switches would be
set
for
18.0
(10
on
S8, 8
on
SlO
and
0
on
S9).
For
-
units
with
serial
numbers
133
and
below,
the
unattenuated
output
level
is+
18
dBm;
thus
an
attenuator
setting
of
I8
would result in
an
output
level
of
O
dBm.
Note
that
turning the switches clockwise in-
creases
the
output
level; turning
them
counterclockwise decreases
the
output
level.
2.3
CONNECTORS
Front
and
rear
panel
connectors
are identified
in
Figure 2-1.
Two
audio
output
connectors,
J7
(LOUT)
and
J8
(ROUT)
,
are
provided
on
the
front
panel.
The
mating
connec
tor
for
J7
and
)8
is
Switchcraft
part
no.
05CL3M,
available from Switchcrnft dis-
tributo
rs or
Potomac
Instruments.
AC
input
(J9)
and
AC
output
connectors
are
provided
on
the
rear
panel, as well as a binding
post
for
chassis ground.
2.4
FUSE
LOCATION
A 1
/8
amp,
250V
fuse is accessible in a
sc
rew-type
holder
on
the
generator
r
ea
r panel.
2.5
OPERATING
PROCEDURES
2.5.1
Turn-On
Procedure
To
place
the
Audio
Generator
into
operation,
proceed as follows:
a.
Check
that
the
power
switch
is
in
the
OFF
position.
b.
Check
that
the
nameplate
AC
supply
voltage
rating
agrees
with
the
supply
voltage source
to
be
used
;
if
so,
connect the
power
cord.
c.
Tum
power
sw
it
ch
to
ON. The
power
indfoator should light, i11dicating
that
power
is
applied
to
all
circ
uit
s
of
the
Audio
Generator.
d.
Set
the
TEST·
OPERATE switch
to
TEST.
Indicator
DS2
shou
ld light
to
verify calibrated
output
level
for
frequencies
below
20
kHz.
Return
switch
to
OPERA
TE.
Audio
Generator
is
now
ready
to
use. ·
e.
Set
OUTPUT, OHMS, BAL/UNBAL as desired.
f.
Set
ATTENUATOR
switches
for
desired
output
level.
24

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g. Set the FREQ switch to the desired output signal or sine wave frequency range.
h.
Connect signals.
2.5.2 OutputMode Selection
The setting of the OUTPUT selector switch, S7, will depend on the particular application and
test set-up in which
the generator is used. In general, differential gain and phase measurements can be
made on stereo systems using the L+R output configuration and an analyzer such as the Potomac Instru-
ments
AA - 51 . The L-R output configuration provides opposite-phase signals which can be passed through
the equipment under test and summed in a simple resistor network to provide a phase-sensitive output
voltage; this technique is useful for stereo record head azimuth alignment. Any measurement involving
the application of a signal alternately to left and right channels may be accomplished using the L and R
switch positions.
2.6 APPLICATION NOTES
2.6.1 Distortion Measurements
Harmonic and intermodulation distortionmeasurements in which the right channel output is
used are best made
with the OUTPUT switch in the L+R position since the residual distortion due to
the AG-51 is lowest in this mode. The residual distortion may also be slightly reduced by maintaining
a minimum
of 1-2 dB attenuation in the I dB-per-step attenuator.
2.6.2 Output Circuit and Termination
The AG-5 I output circuit does not contain a transformer. To understand its operation, how-
ever,
the output terminals (connector pins I and 3) may be thought of as being driven by a center-tapped
transformer winding. In
the UNBAL mode, pin J, or one side of this imaginary transformer winding, is
grounded
to the chassis; in the BAL mode, the center-tap is grounded to the chassis. In both cases, the
open-circuit voltage between pins 1 and 3 is the same, and the source impedance between pins 1 and 3 is
600 ohms or 150 ohms, as selected by the OHMS switch. Any load may be driven without affecting the
AG-51 's distortion, but the output level obtained by subtracting the attenuator di al settin gs from +20 dBm
or 0 dBm is correct only for the terminations of 600 ohms or 15 0 ohms, respectively.
On the test cable supplied with the AG-51, connections are indicated by the color of the
alligatorclip insulators; red is pin I,
blue is pin 3 and black is the cable shield, which is grounded to the
chassis.
The output voltage across any load resistor RL can be calculated from the formulas:
e0 = .7746 2Rt antilog p (600 ohms)
600+RL
20
e0 = .387
2RL
antilog p (150 ohms)
IS0+RL 20
where
Pis the power in dBm obtained by subtracting the attenuator switch settings from 20 (600 ohms)
or zero (150 ohms).
2-5

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For
unbalanced
loads,
use
the
UNBAL AG-51
mode.
If
the
load
has
an
input
transformer
with
a floating
primary
winding,
either
UNBAL
or
BAL
mode
may
be
used
.
If
the
input
transformer
primary
winding
has
a
grounded
center
tap
,
however,
the
BAL
mode
must
be used.
For
600
ohm
operat
ion
the
test
cable
capacitance
reduces
the
AG-5 1
output
at
20
0
kHz
by
0.6
d B
with
no
load,
or
0.15
dB
with
a
600
ohm
load.
At
150
ohms
this
effect
is negligible.
2.6.3
Stereo
Tests
With
the
LOUT
and R
OUT
terminals
connected
to
the
inputs
of
a
stereo
generator
or
excit
er
,
various
tests
can
be
performed
using
the
modes
of
operation
selected
by
the
OUTPUT
switch.
Th
e L+R
mode
yields
main
carrier
modulation
without
subcarrier
modulation
(L-R
:o:
zero),
while
the
L-R
mode
yields
subcarrier
modulation
without
main
carrier
modulation
(L+R =
zero).
Th
ese
modes
are useful
for
modu
-
lator
adjustments
and
for
main
/
sub
and
sub/main
crosstalk
measur
eme
nts.
The
L (R =
zero)
and
R
(L
=
zero)
modes
are
us
ef
ul
for
cross
talk
and
separation
measurem
ents.
2.6.4
EquipmentPerformance Measurements
Equipme
nt
P
erformance
Measurements
(EPM)
to
determine
a
broadcast
facility's
audio
per-
formance
are
required
by
the
FCC
and
described
in
various
sections
of
the
FCC
Rul
es,
Part
73.
These
tests
are
commonly
ref
e
rred
to
as
an
"Audio
Proof''
although
the
FCC
pref
ers
to
use
the
term
"Proof'
only
for
mea
s
urements
to
verify
th
e
performance
of
AM
directional
antenna
systems. Useful guides
to
these EPMs
for
AM
and
FM
stations
have
been
prepared
by
Broadcast
Engineering Magazine
and
ar
e
available
from
Broadcast
Engineering, P.O.
Box
1290
I, Overland
Park
, Kansas
66212.
2.6.5
Grounding
When
the
AG-51
power
co
rd
is
plugged in,
the
chassisis
connected
directly
to
the
AC
power
neutral
line
through
the
third
wire
of
the
power
cord
.
This
may
or
may
not
provide
minimum
power-
frequency
(hum)
pickup
in
the
signal
circuit
.
Often
the
AG-51 chassis
must
be
grounded
so
lidly
to
the
chassis
of
the
equipment
it
is driving
to
obtain
minimum
hum
pickup.
This
connection
may
be
made
using
the
shield
of
the
test
cable.
which
is
connected
to
the
AG-51 chassis,
or
by
using
a
separate
wire
on
the
ground
binding
post
on
the
rear
of
the
AG-5
1.
It
may
also
be
done
by
using a three-prong-to-two-
prong
adapter
for
the
AG-51
pow
er
cord,
and
connecting
the
ground
pigtail
of
the
adapter
to
the
chassis
of
the
equipment
being driven.
If
one
of
the
first
two
methods
are used
the
adapter
may
sti
ll be
required
to
break
the
power
cord
ground
connect
ion
to
obtain
minimum
hum.
In
any
case,
obs
erve
the
following
warning:
WARNING
Be
certain
that
the
chassis
of
the
AG-51 is solidly
ground
ed
to
an
earth-grounded
point
before
using
an
adapter
or
other
means
to
break
the
power
cord
ground
connection;
otherwise
, a safety hazard
may
exist.
2-6

www.SteamPoweredRadio.Com
SECTION 3
THEORY OF OPERATION
3.1 OVERALL DESCRIPTION
The electrical circuits of the Model AG- SI are divided into the sections shown in the block
diagram of Fig. 3.1. Briefly, the operation is as follows:
a. A Wien bridge oscillator
(A6) capacitively tuned over a 10:I range plus decade switching
provides
the variable sine wave source from 20 Hz to 200 kHz .
b. The
IM signal consists of 60 Hz and 7 kHz mixed in a 4: 1 ratio. These two frequ enc ies
are generated by fixed tuned Wien bridge oscillators (A4).
c. A fixed
tuned Wien bridge oscillatorgenerates the 3 .1 S kHz frequency (A4).
d. These sources provide
the optional inputs to the POWER AMPLIFIER (A2) and
INVERTER (A3) through step attenuators S8, S9 and SIO.
e. In TEST mode, the attenuators are bypassed by S4; the maximum voltage output of the
INVERTER is monitored by a window comparator (AS) and, if correct, lights the
LED indicator .
f. Output signal conditions are controlled by three switches (SS, S6, S7) which establish
Land R, BAL or UNBAL, 600 or 150 ohm impedance at the two output connectors.
g. An additional stage of attenuation, part of S8, is placed in the right and l eft channel output
lines. The four switchable attenuator stages allow adjustment of the output level in 0.1 dB ,
1
dB and IO dB steps from a maximum of+ 18 dBm to a minimum of -99 .9 dBm (1 SO ohm
position).
3.2 DE T AILED THEORY OF OPERATION
3.2.1 Variable Frequency Wien Bridge Oscillator (Ref. Figure 4.14, A6; Figure 4.16, A7)
The Wien bridge oscillator circuit is lo cated on A6. Oscillator frequency is determined by
Cl, a dual variable capacitor, in conjunction with decade resistors switched by S2. Cl is used to vary
frequency over a I
0: 1 range, while the resistors are switched in four decades to cover the tuning range of
20 Hz to 200 kHz.
Ql, a JFET, in combination with Q2, a PNP transistor, provides impedance conversion to isolate
the high impedance of the Wien bridge from the following circuits. One side of the bridge is grounded and
the other side must be provided with an in-phase signal with sufficient gain to overcome the bridge loss es
in order to oscillate. This gain is provided by voltage amplifier U IA on A7. The output of U lA is full
wave rectified
by CRl, CR2 and U2 . In addition, UIA drives the bridge with the necessary in-phase signal.
U1B compares
the rectified signal to a de reference voltage, integrates the difference, and controls Q1, a
voltage
dependent resistor. Ql, in conjunction with R4, is an attenuator which adjusts the effective gain
of UIA to just offset the bridge losses resulting in sine wave oscillation. The integration cons tant is switched
to optimize loop stability, distortion , or response time. The output of UlA is low pass filtered by active
filter Q3
and Q4 (A6) and provided at a low imp edance as the oscillator signal to t he power amplifier.
3-1

www.SteamPoweredRadio.Com
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www.SteamPoweredRadio.Com
3.2.2
Fixed
Frequency
Wien Bridge Oscillators
(Ref.
Figure
4.10,
A4)
UI, U2
and
U4A
are
operational
amplifiers
configured
as Wien bridge oscillators.
Negative
feedback
is
controlle
d
by
means
of
an
incandescent
l
amp
(LRI,
LR2,
LR3)
and
a
potentiometer
(R3,
R9
, R 18).
The
potentiometers
are
adjusted
for
a specific
output
signal
and
the
lamp
compensates
for
circuit
variation
s
to
maintain
the
preset
amplitude.
RC
values
in
the
non-inverting
amplifier
input
set
the
operating
frequency
in a
cc
ordan
ce
with
the
formula:
f =
I/
2
1r
RC.
The
IM
signal
is
generated
by
add
i
ng
60
Hz
(U2)
and
7
kHz
(U
I)
in a
4:
1
ratio
by
summing
amplifier
U3.
TP3
allows overall
test
set
calibration
of
intermodulation
distortion.
U4B
buffers
the
3.15
kHz
signal used
for
wow
and
flutter
refer
ence.
3.
2.3
Power Amplifier (Ref. Figure
4.8,
A2,
A3)
The
input
signal is applied
to
the
base
of
Q
1,
part
of
differential
amplifier
QI
and
Q2. Q3, a
PNP
transistor
,
provides
additional
voltage gain.
Q4
is
utilized
as
a
constant
cu
rrent
source
and
provides
very high
imp
eda
nce
collector
load
for
Q3.
QS
and
Q6
are
complementary
power
transistors
r
equired
to
drive
the
output
load.
Forward
bias
provided
by
CR
I
eliminates
cross-over
distortion.
Negative feed-
back
via
R2
to
the
base
of
QI
sets
the
closed
loop
gain
to
5.5.
Pow
er
supply
voltages
of
±30V
are
ne
cess
ary
to
provide
the
required
output
pow
er
of
+20
dBm*
into
a
600-ohm
resistive load.
QS
and
Q6
employ
heat
sinks
to
prevent
excessive
junction
temperatures.
An
identical
amplifier
driven
by
voltage
divider
Rl4
and
Rl5
permits
balanced
operation.
3.2.4 OutputMonitor (Ref. Figure 4.12, AS)
Since
the
two
output
amplifiers
operate
in
ser
ies,
it
is possible
to
monitor
the
overall
operation
by
rectifying
the
inverter
output
by
CRl
.
U2A
filters
the
ripple
frequency
and
furnishes a
low
impedance
source
for
the
window
comparator
U2D
and
U2C.
The
window
comparator
is furnished an
independent
and
stable
de
reference
signal
by
voltage
regulator
Ul.
The
window
bracket
is
±0.5
dB
and
is
adjusted
for
sine wave
or
IM
signals
by
potentiometers
R7
and
R8.
U2B provides
sufficient
current
to
light
the
LED
indicator
on
the
front
panel.
The
monitor
check
is
made
at
maximum
voltage
output
of
the
ampli-
fiers
and
is
enabled
by
the
TEST/OPERA
TE
switch,
S4
,
which
also removes
the
attenuators
from
the
amplifier
input
circuit.
This
is
necessary
as
the
amplifier
output
voltage is
normally
a
function
of
the
ATTENUATOR
setting. AS
contains
Ql,
Q2,
Q3
and
Q4,
which
serve as
unity
gain
buffer
amplifiers
to
isolate
circuit
loading
from
the
attenuators
(Ref.
Figure
3.1
).
3.2.5 Output Attenuation Switching(Ref. Figure
4.17)
Output
attenuation
is
provided
by
two
groups
of
switchable
resistor
networks;
one
which
acts
on
the
oscillator
output
signal
before
it
is applied
to
the
power
amps,
and
another
acting
on
the
output
of
the
power
amps.
On
the
input
side
of
the
power
amps,
the
finest degree
of
attenuation
(.1
dB
incre
-
ments)
is
controlled
by
S9.
S9
is a
switc
habl
e resistor
network
through
which
the
selected
oscillator
output
signal
must
pass
before
it
is
applied
to
amplifier
stage
Ql/Q2
in
the
AS
module.
The
l dB
step
attenuator
network,
SIO
,
acts
on
the
output
of
Ql/Q2
and
provides
the
input
to
amplifier
stage
Q3/Q4
,
which
in
turn
drives
the
power
amp
A2.
The
10
dB
step
attenuator
network
,
S8,
acts
at
two
points
in
the
circuit.
The
60
through
90
dB
steps
act
on
the
input
to
S9
and
Ql/Q2,
while
the
O
through
50
dB
steps
act
on
the
output
of
the
power
amps
A2
and A3.
3.2.6
Output
Mode
Switching
Output
mod
e is
selected
by
OUTPUT
switch
S7.
ln
the
Lor
R
position
,
S7
connects
the
output
of
power
amp
A2
to
either
the
L
or
R
output
jack
(pin
3)
while
grounding
the
unused
output.
In
the
L
+R
*+
18
dBm
for
units
wi
th
serial
numb
e
rs
133
and
below.
3-3

www.SteamPoweredRadio.Com
position, S7 connects
the
output
of
A2
to
pin
3
of
both
Land
R
output
jacks. In
the
L-R position,
the
A2
output
is applied
to
the
L
output
jack, and
the
A3,
or
inverse
output
, is applied
to
the
R
output
jack
on
pin
3.
When
the
BAL-
UNBAL switch, SS, is in
the
UN
BAL
position, a
ground
will
be
applied
to
pin
1
of
the
L
and R
output
jacks. When
SS
is in
the
BAL
position, this ground is removed from
pin
I
and a signal determined
by
the
position
of
S7 is applied.
The
signal applied
to
pin 1will always
be
the
inverse
of
the
signal applied
to
pin 3, e.g.,
if
the
output
of
A2
is applied
to
pin 3,
the
output
of
A3 will
be
applied
to
pin
1.
This provides an
output
across pins
I
and 3 which is balanced with respect
to
ground.
Output
impedance is determined
by
S6, which selects
an
output
circuit
path
either
directly
from S8, giving
600
Ohm impedance,
or
through
a resistor
network
whjch provides
a
150
Ohm
impedance.
3.2.
7 Test/Operate Switching
The
TEST/OPERATE switch, S4, disconnects
the
generator
output
and supplies a ground
to
the
output
impedance network,
S6,
when
placed in
the
TEST position.
Tt
also provides a signal
path
bypassing
the
attenuator
networks
(S8,
S9, S10)
on
the
input
side
of
th
e
power
amps when in
the
TEST
position, so
that
the
maximum
output
signal level is available
to
the
output
level
monitor
circuits in
the
AS
module.
3.2.8
Regulated Power
Supply
(Ref.
Figure
4.6,
Al)
A
center
tapped
transformer
(Ref. Figure
4.17)
converts
the
115
V
ac
line voltage
to
48 Vrms.
This secondary voltage is applied
to
CRl
and
CR2
which provide full wave rectification. Capacitor C
1
filters
the
positive 30-volt
output.
Rl
is
a bleeder resistor, while
Rl2
provides
current
to
the
LED power-on
indicator.
The
decoupling network
of
R2
and C3 provides
input
de
to
integrated regulator circuit UI. A
positive regulated voltage
of
15 volts is provided
for
all analyzer circuits.
CR
7 prevents negative latch-up.
The
variable voltage divider circu
it
composed
of
R3,
R4
and RS provides
an
adjustable reference voltage
for U
1,
allowing
adjustment
of
the
supply
output
voltage. C7 filters
the
reference voltage
to
ensure
stability.
The
regulated negative
15
volts is derived
by
an
identical circuit
except
for
polarity
of
components.
3-4

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4.1 GENERAL
SECTION 4
MAINTENANCE
The troubleshooting procedures given in this section should enable a qualified technician to
determine t he specific component or adjustment responsible for a malfunction. Replacement of
components in a modu le or performance of alignment procedures should not be attempted unless the
equipment specified for performance of the module alignment is available. If there is any doubt as to
the advisability of a maintenance operation, factory consultation or service should be sought
(RE F . page ii).
4.2 PERIODIC MAINTENANCE
The AG-5 l has no periodic maintenance requirements.
4.3 ALIGNMENT PROCEDURE/PERFORMANCETEST
The following procedure may be used to perform alignment of the AG-51 and to verify
generator performance. Alignment should be attempted only if accurate test equipment of the type
specified, and qualified personnel, are available.
Test and adjustment points may be located by referring to Figure 4.3 or to the appropriate
component location diagram.
4.3.1 Power Supply
a. AdjustR5for+l5VDC±20 mVatPin6.
b. Adjust R6 for -15 VDC ±20 mV at Pin 18.
c. Check for approximately +30 VDC± 1 VDC at Pin 8.
d. Check for approximately -30 VDC±1 VDC at Pin 16.
4. 3.2 Oscillator Pre-Amplifier, A6
The following procedures require the use of a calibrated frequency counter or other means
for accurate frequency measurement (±3%, min.).
FRONT PANEL CONTROL SETTINGS
ADJUST CHECK
VALUE
POWER ON
C3
Gen . outout 20 kHz
FREQ XI00 (20 kHz)
LOW DIST/FAST RESPONSE LOW DIST
OUTPUT L+R
BAL/UN BAL UN BAL
OHMS ~O
TEST/OPERATE OPERATE
ATTEN
4-1

www.SteamPoweredRadio.Com
a. Monitor
the
generator
output
using
the
frequency counter. Set
the
generator
FREQ
dial exactly
at
200.
Adjust
C3
on
A6
for a reading
of
20,000
Hz
on
the
frequency counter.
b. Turn
the
generator
FREQ
dial
to
various intermediate settings and check
that
generator
output
frequency is within 3%
of
the
dial setting.
In rare instances, it may be necessary
to
adjust
the
mechanical alignment
of
th
e
FREQ
dial
in
order
to
achieve accurate frequency tracking. This procedure should
not
be
attempted
unless all
other
possible sources
of
error
have been eliminated and personnel are available with experience in this type
of
adjustment. The procedure
is
as follows:
a.
Set
the
generator
FREQ
switch
to
XI
00
and
set
the
output
frequency carefully
at 2
kHz.
b. Loosen
the
two
set
screws holding
the
frequency dial coupler
to
the
shaft
of
the
variable capacitor
Cl
and
set
the
dial
at
20;
see
that
frequency remains
2000
Hz.
Adjust
the
variable capacitor position
for
a reading
of
2000.0
Hz
on
the
frequency
counter
.
c. Tighten screws
on
the
FREQ
dial coupler and proceed with
the
regular frequency
alignment procedure described above. Steps (b) and (c) may have
to
be
repeated
on
other
ranges and a best compromise reached in conjunction with Step (a).
4.3.3
Control AmplifierBoard, A
7
The
following procedures require
the
use
of
an accurate
RMS
voltmeter (±3% min.),
a
600
ohm load
(1%)
and an accurate frequency counter.
FRONT PANEL CONTROL
SEfTINGS
POWER
FREQ
LOW DIST/FAST RESPONSE
OUTPUT
BAL/UNBAL
OHMS
TEST/OPERA
TE
ATIEN
ON
As required
LOW
DIST
L
+R
UNBAL
600
TEST
~
ADJUST CHECK VALUE
R20
Gen.
output
20dBm
R2
Jl-2
(R22)
-2VDC
Cl
1
Gen.
output
20dBm
a.
Monitor
the
generator
output
using an RMS voltmeter and
600
ohm
load. Set generator
frequency
to
1kHz.
Adjust
R20
on
the
A7
module for an
output
level
of
+20
dBm*.
b.
Set
generator frequency
to
200
kHz. Using a DC voltmeter,
monitor
the
voltage
at
pin
J
1-2
of
A7
or
at
either
end
of
R22
and adjust
R2
for
a reading
of
-1
VOC.
This
voltage should vary approximately
-1
V
to
-3V
over
the
whole frequency range.
R2
may
be
adjusted
in
some cases
for
minimum distortion.
c.
Set
FREQ
to
Xl000
and dial
to
200
and
adjust
Cl
I
on
the
A7 module for
a
generator
frequency
of
200
kHz.
*+
18
dBm
for
units
with
serial numbers
J
33
and
below.
4-2