Gould J3B User manual
'
L.F.
SIGNAL
GENERATOR
J3B
Instruction
M a
nua
I
•}
GOULD
ADVANCE
Roebuck Road, Hainault,
Essex
..
Telephone: 01-500 1000
Telex: 263785
Telegrams: Altenuate Iiford.
FOR
SERVICE
MANUALS
CONTACT:
MAUR!TRON
TECHNICAL
SERVICEf
www
.mauritron.co.uk
TEl.
01844
·
351694
FAX: 0i
844
-
352554
Contents
SECTION
INTRODUCTION
SECTION 2
SPECIFICATION
3
SECTION 3
OPERATION
4
3.1
Switching On 4
3.2 Block Diagram 4
3.3 Selection
of
Frequency 5
3.4 Balanced
Output.
15-0-15v
rms
emf.
5
3.5
Low-Z
Output
3V
rms
emf.
Zo
""
10hm
6
3.6
Low Distortion Output 2.5V
rms
emf.
Zo~5K
Ohm
6
3.7 Square
Output
0
to
+SV Z
Zo<>1K!J
6
3.8
Output
Level
Meter
& Decibel
Scale
6
3.9 Relative Phase 6
SECTION 4
CIRCUIT
DESCRIPTION
7
4.1 Wien Bridge Oscillator 7
4.2
Power
Amplifier
7
4.3
Power Outputs 8
4.4
Square Wave
Output
8
4.5
Power
Supply 8
4.6
Meter
Circuit
9
4.7
Mains
Input
9
4.8
External D.C.
Supply
9
SECTION 5
MAINTENANCE
10
5.1 Removal
of
Covers 10
5.2 Removal
of
Oscillator Box
Cover 10
5.3 Removal
of
Printed Circuit
Board
Assemblies
10
5.4 Setting up
of
Wien Bridge FOR SERVICE MANUALS
Oscillator 10
5.5 Setting up
of
Power Supply
11
CONTACT:
5.6
Setting
up
the
Power
Amplifier
11
MAURITRON
TECHNICAL
SERVICES
5.7
Setting
up Squarer
11
5.8 Distortion 11·12
www
.mauritron.co.uk
TEL:
01844-351694
SECTION 6
COMPONENTS
LISTS
and FAX:
01844-352554
ILLUSTRATIONS
13·18
SECTION 7
GUARANTEE
AND
SERVICE
FACILITIES
22
ILLUSTRATIONS
Fig.1 Power
Supply
Tappings, links,
and Fuse ratings 4
Fig.2 Block Diagram 4
Fig.3
Graph
of
Distortion
and
Frequency
12
Fig.4
Component
Location Diagram 19
Fig.5
Circuit
Diagram
21
'
2
Introduction
The
Gould
Advance
J
38
Signal Generator
is
an
LF
instrument
mcorporating
a high
output
level
from
a balanced, floating
600
n
output.
The
main
output,
which
is
metered,
gives
15V
into
SOC
n
(30V
EMF).
The frequency range
of
10Hz
to 1OOkHz
is
provided
on
four
decade
ranges, and
the
6: 1
reduction
drive
with
capacitor
tuning
gives high resolution
of
frequency
with
minimum
bounce.
Three
additional
outputs
are available, a
lW
low impedance
output,
a
square
wave
output
and
a
low
distortion
output.
The
solid
state
circuitry
results in low
heat
dissipation,
giving a
high
order
of
frequency
stability
and
reliability.
Switched
step
attenuators
give 60dB
of
attenuation
and
the
variable level
control
can
be used
to
provide a
further
20dB
of
attenuation
with
negligible
hum
and
noise on
the
output.
'
Section1
FOR
SERVICE
MANUALS
CONTACT:
MAURITRON
TECHNICAL
SERVICEf
www
.mauritron.co.uk
TEL:
01844-
351694
FAX:
01844-
352554
f
r
I
I
I
I
I
I
!
-
f
~-
l
[
Components List and Illustrations
:::f
11)01
..
"''
~104
"
~,'
~ ~
'""
"
,.,.
''"'
~=
' --
I
I
I
I
I
I
I
U•PUT
I
Ron
--·-
I
I
lO•
...
:>-''~0~0~·-----
lOU
,...
.....
,
•oo
..
; •
''io'"'
~-
0
-~
\G
..
o
I{ICOMO
C>OJ
c
"'
"
Section
.,,.
••o•
~~~·
11101
11"0
IIIII
••u
••••
"'
••u
••·l
..
,
.
..
,
""
:11
coot C•o•
c•o•
co
11
"
Cl
CJ
C•
CH
Clo
TAIO)
roou
TRilJ
1',-,,o,~--~1.-oo-,---
rt"o~-,---------
~
_k
11101
:!:·
·:;
_r,_,_
-\:5
Cl1l
.
"'"
"'I'
'
L--
_..J
L
_______
_
Jstrations
Section
6
co•
0~
()ISTQQTOQ><
0/P
S~~
SKG
l
::
I
FHO&ACl
A•H
"'·I
,.,.
•.
anJ
••17
••10
~111
"''
•o
AMPLIFIER
(IR(UIT
!
~·
-I
""
Ant
~1'\
-4S
~
...
"'"'
An
...
IT(
A
....
....
-·~0~~--.~.~
..
~-----c
••
~.~
••
~~.~
..
~.~~.~
..
-.-.-,~----~
lQI$1
TR06)
TAIU
0111
OoU
METER
Clfi.CUI
I
"'ill
POWER
SUPPLY
CIRCUIT
r
AI&•
TIIIU
I .
..~
_t
~-,
ttl....
:::
!~n.~.~~
~
~~~=======i~·f·~~-~·=~~===j~-~'~
.__
,.
r--.
~
~::
·~
....
§5.i
....
r
r·
-1
:
~~~::"
'"
~
f''~
I
i•
•
f--1
.AIOoTHl
CI"CUFT
.OAAO
AU(-I.T
-
lltlJ
i
....
+--l-J+l---------1 l 'o•
""
""'
l,i
' L___'
"" ""
'""
~""
~
..
I:·
~-
..
:~"-_--
_
_._...J_'-_-_
-~L-_----'
__
"-_-T=
..
=t-=+_
,=_
G~u~,,~,_=_l'~'
....
_
-_-_-_-_--!:_==_==_==_==_=_=_=_==~~====~~=f--J.-;;,
..
;;;,;;;=d---t
I
I ' - - - - - - - - - - - -
--
-
--
_.,,_,__•
-
I , . ,
••
, ,
~
'
L';.'~"
~
. .
~,oe---·
I
"'
'1-
.
=-~~--,-----~~~~.·
i -
.·~·
.1:~--
~~-==-~--
=::====~"'====-======~·'
1:--
""'
~
,---<:':':j.--Li-1
.....
-
--
,----_-r--------r---_-_-_-_-_-
__
-
__
-_,-r---,-----;----f~.~-_,----~-~·;;;~-c::-o-1'
'
J;:r1.,.
1.,.
...
\;' •,
.1
"'
c:tJ
•"
d
~·
,-----1----------J
1:u
~
,i
"'
~
·:5
r---l
lc
._,,
~-
--~-----------~
...
,-L-, I
' ' L -
"'
•ouNTtD
CIAC\IIT
IOAOO
AISIIWILT
N•.
10011
.,
---------1.
6
.........
Ani
...
,
"'
'!.)_4
..
-,-01
'~
~·-;
c
'"
c
'09
''"
1CJJ
"'
'"
-
()I')
I
OIOJ
UoQ4
0•>•
'"
'"'
·~
Rl10AIJI
.',,
""'
AoH
"''l
""'
"'
...
..
,
"'
"'
'"
...
'"
'"'
"'•
'"'
'"'
c
"'
'"
"'
"'
"'
c
~0
OIQJ
•••ot
:»o•
OtOI
!RoOT
TIIIOI
'"
WilT(
A
""'"'fD
''"'"''
~o<>•Ao
IIU-~T-
JltZJ
'"
....
....
"'"'
...
...
"'"
C•oJ
.....
"
'"'"
...
-
..
f:-
.....
ur
"'
,,
••u
...
UIU
TAou
•
114
....
•••o
""'
"'
...
,,
..
,,,,
,,
..
0111
o•n
··~
Oil)
DIU
...
Ill
,------,
METER
CIRCUIT
CIRCUIT
()'··
1
f.---J'~
I
.,
..
+
CIU
II.IU
I
I
I
I
.
I
J I
I
I I
'
I
I
I
I
I
I
I
I
I
I
I
0::.'"~'
L~t'J""
r:J-~+-"'~
~
....
'
r·
I
... ...
2~
~
Q
j...
..
~
...
;;,:.
~~~
~r---
1"''11
,J.,
r.
'"
r
! f
.,,.
••o
'"
-
"'
--.
.
I~
- I
'
~"'
OSCILL.TQA
'"IIHlO
CI.CUIT
IOA•O
oU~WILT
.....
1091\
.----,
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
,
-L
I
:
"'"
I
I
--
- - - - -
--
- - -
-i;-~:-
-
_J
+
...
..
"'
f"
+
JJV
OOOTU
1.(4
..OT
,ITT€0
Of< ...,_L UOU
J.
Cl
IS
A
~l...;T
..
o•
COOU.IAI
C
FOR
SERVICE
MANUALS
CONT/,CT:
MAURITAON
TECHNICAL
SERVICE/:
www
.mauritron.co.u\;;.
TEL: 01844 · .':\51694
FAX:
01844
·
352554
21
F1g.
5
Circuit
Otagram
Specification
FREQUENCY
Range:
10Hz
to
100kHz
in 4
decade
ranges.
Common
320°
circular
scale
for
all
ranges.Scale:
Setability:
To
1
part
in
10
4
Accuracy:
2%
of
reading
+
1HZ
Typically
1%
+1
HL
OUTPUTS
1)
MAIN
OUTPUT
30V
r.m.s.,
e.m.f.
(15-0-15V)
from
balanced floating
output
of
impedance
300-0-300
Ohms
(15V
r.m.s.
into
600
~!load).
Output
Impedance
tolerance:
5%-
Balance 3%
Balanced
Attenuator:
20dB and 40dB (60dB
total).
Accuracy:
0.3dB
and
0.5dB
respectively,
each
half.
Fine level
control,
from
0
to
full
output
(Common
to
Outputs
1,2 and 3).
2)
LOW
IMPEDANCE
OUTPUT
3)
41
3V
r.m.s.,
e.m.f.
from
approximately
1
Ohm.
With
Output
1
fully
loaded,
Output
2
will
deliver
a
typically
of
1
Watt
into
5
Ohms.
LOW
DISTORTION
OUTPUT
(at rear
of
instrument).
typically
2.5V
r.m.s.
from
approxir:1ately
5k
~!.
Overall flatness
0.3
dB.
SQUARE
WAVE,
0
to
+5V,
independently
controlled.
Source
Impedance
approximately
lk~!.
Rise
and
Fall
times
better
than
1>-<s
into
less
than
lOOp F. Mark-
space
ratio
better
than
1.1:
1.
NOTE:
Section
2 3
OUTPUT
LEVEL
METER
Scaled
0-30V
r.m.s.
Open
Circuit
for
Output
1.
Scale
also
common
to
Output
2.
Decibel
scale,
referred
to
+20dBm
into
600
il
The
meter
accuracy
is
3%
ofF
.S.D.
DISTORTION
1I
2)
Outputs
1
&2:
less
than
0.1%
above
100Hz
rising
to
less
than
0.5%
at
1OHz.
Typically
better
than
0.05%
from
200Hz
to
100kHz
Low
Distortion
Output:
Typically
better
than
0.02%
above
200Hz
rising
to
0.2%
at
10Hz.
PROTECTION
All
outputs
rated
for
full
load
simultaneously
All
outputs
Short-Circuit
proof.
Visible
indication
of
overload
on
Output
Level
Meter
(Intermittent
reading).
SUPPLY
VOLTAGE
85-130V
and
170-255V
40-400Hz,
approximately
20VA.
Also
42-52V
.
DC/300mA
Max.
OPERATING
TEMPERATURE
RANGE:
DIMENSIONS
27 x 27 x 13 ems 110.7 x 10.7 x 7.2 in.)
WEIGHT
6kg (131bs.)
All
outPut
levels
are
flat
within
ldB
over
the
full
frequency
range.
Below
30Hz
the
maximum
output
level
may
not
be
available
on
full
lead,
on
outputs
1 & 2
(typically
20V
available
at
1OHz).
FOR SERVICE MAI\IUALS
'
MAURITRON
T!?Cf!~ICAL
SERVICES
www.mauri"lron.co.uk
TEL:
0184A
351694
FAX:
01844-352554
4
Operation
3.1
SWITCHING
ON
(i)
Make
sure
that
the
voltage
supply
tap
on
the
transformer
is
set
correctly,
and
that
the
correct
fuse
is
used.
The
transformer
is
accessible
upon
removal
of
the
top
cover
of
the
instrument.
(see
5.1).
Unless
labelled
otherwise,
the
J3A
is
delivered
for
234V
+ 10%
(See Fig. 1
for
transformer
taps,
links
and
fuse ratirlgsl.
In
addition,
an
over-voltage
tap
(41V)
IS
available
on
the
secondary
Winding,
which
effectively
extends
the
range
of
effectively
extends
the
range
of
supply
voltage
to
-20%.
(ii)
Set
the
support/carrying
handle
to
the
required
operating
position.
The
handle is released
by
pulling
both
fixing
bushes
outwards,
and
it
can
then
be
turned
to
lock
in
any
one
of
three
positions.
(iii)
It
is
advisable
to
turn
the
Output
Level Fine
control
to
minimum
before
switch·on,to
avoid
large surge
outputs
for
the
few
seconds
that
the
oscillator
takes
to
stabilise.
(iv)
The
Instrument
is
ready
for
use
half
a m1nute
after
switching
on
and
fully
'settled'
within
five
minutes.
No
special
precautions
with
cooling
need
to
be
taken
normally
but
natural
ventilation
should
not
be
restricted
when
operating
at
high
ambient
temperatures.
3. 2
BLOCK
DIAGRAM
The
broad
outlines
of
the
instrument
are shown in
the
block
Diagram in Fig. 2.
Power
is
supplied
by
a Regulated
supply
which
includes
the
protection
circuits.
The
low
distortion
output
from
the
Wien
bridge
oscillator
of
variable
frequency
is
taken
through
a
front
panel
Fine
Output
Level
control
to
-
-II>--
'
POWER
SUPPLY, SERIES REGULATOR
EXT!:
D.C.
So
PROTECTION CIRCUIT
.--
--
9
0/P
+31V
POWER AMPLIFIER
WIEN
BRIDGE
0/P
0/P<r
-
OSCILLATOR
0/P
..
..
LEVEL
2-
l
Section
3
Fig. 1
Power
Supply
Tappings,
links,
and Fuse ratings
36V Secondary Tap.
195-230V
(170-210)
n;;,
255V
Figures in
brackets
refer
to
use
of
41V
secondary tap.
the
Power
Amplifier,
which
drives
the
transformer·coup!ed
power
outputs
and
the
Meter
circuitry.
The same
oscillator
drives a
Squarer,
the
level
being
adjustable
through
a second
front
panel
control.
L
i Mains METER
N
r-
CIRCUIT
e
r
-
II
<>
f-o300n
II
~
+22V
~
~
SQUARER
C.T
'--
f-oi/P
0/P()-
-
~
~
-
~
~
<>
f-o
JOOn
ATifNUATOR
2:--
~
l
CCNY
OISTORTK>N
0/P
LOW·Z
0/P
=-
O(P
Fig. 2
Block
Diagram
'
'
I
l
I
I
I
I
I
r
;
......
l
r
\
'
•
Operation
3.3
SELECTION
OF
FREQUENCY
To
set
frequency,
the
Range
Switch
is
turned
to
the
appropriate range.
The
fine
control
of
Frequency
is
a
circular
dial
which
is
set
at
the
desired
part
of
the decade
in
use.
Although
the
accuracy claimed on the dial calibration
is
typically
1%,
the
resolution
of
the
gang
capacitor
in
the
oscillator
is
essentially infinite and frequency can be
set
to
any required value
to
within
1:
10
4. It
is
often
convenient
to
use
the
independent
square
wave
output
to
monitor
the
exact
frequency
by
a
Timer
Counter.
3.4
BALANCED
OUTPUT
15·0·15V
r.m.s
.•
e.m.s.,
(i)
Output
1
is
mainly
intended
for making balanced
600
n'
line
measurements.
In
such use
the
desired
amplitude
is
set
on
the
Meter-
remembering
that
half
the
Open
Circuit voltage will
appear
across
the
load-
and
the
balanced
attenuators
are used to give
-7-
10
or...;..
100
facilities.
(i
i)
The
balanced
output
can be used unbalanced,
terminated
in 60011 ,
in
which
case Metering and
the
use
of
the
attenuators
is
exactly
as
above. If a low
level
unbalanced
signal from a
600
source
is
required
from
the
J3A-
i.e. less
than
-40dB-
it
is
advisable
to
use
half
the
balanced
output
with
the
centre
tap
at
the
low
impedance
end,
and
use a
300
resistor
in
series
externally
to
make
up
to
600
Q . This avoids
the
pickup
of
sma!l
spurious
signals due
to
the
unbalance
of
the
output,
which
can be significant
at
high
attenuation.
(iii)
Half
the
balanced
output
can also be used. If
terminated
with
300n,
again
the
Metering and use
of
attenuators
remain
unchanged,
but
of
course
only
half
the
output
voltage
is
being used, i.e.
the
output
is
a
quarter
of
the
e.m.f. indicated.
(iv)
In
addition,
the
balanced
output
can be used
in
any
of
the
above
ways
without
matched
termination,
i.e.
operated
into
any
load
between
open
and
short
circuit
It
would
then
behave like an e.m.f. with a source
impedance
of
600
or
300
n ,
depending
on
whether
the
whole
or
half
the
output
is
used. The
attenuators
remain
operative.
(v)
Finally,
there
is
no
reason
why
different
loads
should
not
be used
on
each half
output,
remembering
that
they
will be in phase
opposition,
and
the
resultants
either
measured
or
calculated.
(vi)
The
e.m.f.
from
the
bifilar
transformer
secondaries
is
essentially
balanced.
The
output
resistances
at
the
terminals
are
balanced
to
within 3%. Each
attenuator
may
introduce
unbalance
of
3%
in
e.m.f.,
but
the
unbalance
of
output
impP.dance remains unchanged,
at
a
maximum
of
3%.
Section
3 s
Warning:
1.
The
maximum
voltage applied
between
the
balanced
output
and
ground
must
not
exceed
500V
d.c.
or
peak
a.c.
2.
The
passage
of
direct current
through
~he.
balanced
output
must
be
restricted
to
less
than
50mA,
to
prevent
damage
to
the
output
resistors. A
muci"J
smaller
current
than
this, however, can
saturate
the
output
transformers-and
severely increase
distortion.
If
some
d.c.
must
be passed, it
is
an advantage
to
use
the
attenuators
which will effectively reduce
the
current
reaching
the
transformer
by
the
same ratio.
The
permissible d.c.
is
a
function
of
frequency
and
acceptable
distortion,
and can best
be
found
by
experiment.
3.5 LOW·Z OUTPUT
3V
r.m.s., e.m.f. Z0
<>1
Ohm
(i)
This can
be
used
unloaded,
and
the
e.m.f. can be read
as
1/1 Oth
the
Meter reading.
The
response
is
flat and
the
distortion
less
than
at
the
Balanced
Output.
The
full range
of
amplitude,
i.e.
3V
r.m.s.,
e.m.f.,
is
avail-
able when
output
2
is
loaded by 5 Q
or
more,
simultaneously
with
normal loading
of
output
1.
[f
cutput
1
is
unloaded
and
unattenuated,
the
load
on
output
2 can be generallv
reduced
to
3
Qat
full
output.
Loads smaller
than
3 Q may cause
the
protection
circuit
to
operate,
unless level
is
reduced.
Under
near
short
circuit
conditions
the
maximum
current
available
from
output
2
is
approximately
0.9A
r.m.s.
Below
30Hz
and
at
full
cutput/loading,
the
protection
circuit
may be
trigg~red
at
the
peak
of
a cycle.
Note
When
the
protection
circuit
operates
because
of
excessive loading,
the
output
level
automatically
'cycles
on
and
off'
at
intervals
of
about
2 seconds
This
is
indicated by a
corresponding
swing
on
the
output
Meter.
3.6 LOW
DISTORTION
OUTPUT
2.5V
r.m.s., e.m.f.
z0
<>5k
Ohm
(i)
This
output,
directly
from
the
oscillator,
is
taken
from
the
slider
of
the
Fine Level
Potentiometer
through
a
buffer
resistor.
It
can
be
loaded
without
detriment
to
the
performance
of
the
other
outputs,
although a
change
of
loading reflects
on
the
output
levels.
(ii) An
external
signal from
another
Generator
can be
injected
into
this
output
and
be resistively mixed
with
the
low
distortion
J3A
signal.
The
mixed
signal
is
then
available at. amplified
outputs
1 and 2
to
permit
intermodulation
measurements
on
amplifiers,
etc.
However, leads
left
attached
to
this
output
can pick
up and inject
unwanted
signals and noise
into
the
J3A.
60peration
It
should
be
noted
that
maximum
injection
occurs
with
the
Fine Level
control
at
its mid seuing.
See also
4.2,
last
paragraph.
3.7 SQUARE
OUTPUT
0
to
SV Z0
<>1
K
Iii A
fraction
of
the
oscillator
signal
is
taken
to
the
Squarer
circuit,
and
the
independently
controlled
output
is
made
available
~t
the
front
panel as a
positive-going
square
wave
from
OV
(ground}.
The
mark/space
ratio
and
rise
and
fall
times
(see Specific·
ation)
are
maintained
over
the
entire
frequency
range
of
the
J3A.
If
the
mark/space
ratio
is
preset
to
unity,
the
square
edges 'lag'
all
the
sinusoidal
outputs
of
the
generator
by
approximately
1%
of
the
period+
0.1 us. In
the
1.
10kHz
range, however, because
of
transformer
phase
shift,
the
floating
output
begins
to
lag
the
square
wave progressively,
after
approximately
4kHz,
by
a small
amount.
(ii)
The
square
output,
being
independent
in
level
of
all
the
other
outputs,
can
be
conveniently
used
for
Frequency
Counting,
for
externally
locking an
oscilloscope
time
base,
etc.
'
Section
3
(iii) If
terminated
in
50~2
,
the
square
wave
is
reduced
to
150mV pk. approximately at full
output.
and
the
rise
and
fall
times
improve
to
better
than
0. 1 u s.
3.8 OUTPUT
LEVEL
METER & DECIBEL SCALE
(i)
The
Met~r
effectively measures
the
primary
voltage
of
the
output
transformers
and
is
calibrated
0 ·
30V
r.m.s.
e.m.f
..
the
total
open
circuit
voltage available
at
the
balanced
output.
Items
3.4
and
3.5
above
describe
most
of
the
likely
arrangements
of
load,
etc.,
as well
as
the
use
of
the
matched
and
balanced
Attenuators.
{ii)
The
(red) decibel scale
is
a
'relative'
scale
to
enable
amplitude/frequency
response
measurements
to
be
made
conveniently.
The
OdB
point,
however,
has been
chosen
to
equal
+20dBm,
for
convenience
in
power
measurements
in
600
12
3.9
RELATIVE
PHASE
The
signal
out
of
the
left
hand
terminal
of
Output
1 with
respect
to
the
Centre
Tap,
is
in
phase
with
Outputs
2,
3
and
4 with
respect
to
ground.
FOR SERVICE MANUALS
CONTACT:
MAURITRON
TECHNICAL
SERVICES
www.mauritron.co.uk
TEL: 018.14-351694
FAX:
01844-352554
'
I
l
J
I
I
I
I
r
L
Circuit
Description
4.1 WI EN
BRIDGE
OSCILLATOR
Transistors,
TR
1 -
TR6,
comprise
the
oscillator
amplifier.
Transistor
TR7,
is
a
supply
rail stabiliser.
The
input
of
the
amplifier
goes
to
a field
effect
transistor,
TR2,
which
is
in
a long-tailed
coupling
with
TR3.
TR2
is
driven
in
cascade
with
TR
1,
to
avoid Miller
capacitance
to
the
input
gate.
The
base
of
TR
1
is
d.c.
coupled
to
the
'common'
emitters
of
TR2
and
TR3.
thus
providing
TR2
with
a
constant
emitter-collector
voltage
to
reduce
distortion
with
the
large signal
swing
at
the
emitter
of
TR2
(3Vp-p).
The
signal from
the
collector
of
TAl
is
fed
to
emitter-
follower,
TR4,
with
bypassed
collector
resistance, R35,
serving
to
limit
current
at
switch-on,
before
the
oscillator
d.c. levels are
established.
Diode
04,
from
the
collector
of
TR5
to
the
emitter
of
TR4,
'catches'
the
collector
of
TR5
and prevents it
from
rising and
bottoming
by
almost
the
full Zener
potential
of
02.
TR4
drives
the
base
of
the
transistor
TR5,
which
inverts
the
signal, feeding it
to
the
output
emitter-follower,
TR6.
From
the
emitter
of
TR6
the
signal
is
taken
to
the
input
of
the
Wien Bridge consisting
of
ganged variable
capacitors,
C7
A,
C7B, and
the
switched
Range resistors, R1-RS.
The
range resistors, R1
to
R4, are
returned
to
variable bias
at
T.P. (A) which sets
the
d.c. level
at
the
output,
T.P. (E).
The
stability
of
this d.c. level
is
maintained
by
feedback
to
the
base
of
TR3.
In
the
symmetrical
Wien Bridge
configuration
used
in
the
J3A
oscillator.
the
voltage
transfer
ot
the
bridge
at
'resonance'
is
precisely
1/3.
A
similar
voltage
transfer
is
effected
in
the
feedback
network
comprising
Thermistor,
R44, its
shunt
resistors
R33
and
R34,
and
the
feedback resistor, R30,
thus
maintaining
the
high-gain amplifier in
operational
equilibrium.
If
the
output
level
is
low,
Thermistor
R44,
is
cold
and
hence
its resistance
is
high. This reduces
the
negative feedback
which,
in
turn
increases
the
gain
of
the
amplifier until
equilibrium
is
re-established.
The
opposite
happens
if
the
output
level
is
high.
The
same voltage
transfer
of
1/3
is
also a.c.
coupled
to
the
resistor, R28 (the
'long
tail'
of
TA2,
TR3),
effectively
producing
constant
current
in R28.
The
same
1/3
voltage
is
also applied
through
buffer
resistor,
R31,
to
the
'Guard'
T.P. (C),
which
is
connected
to
guard
screens placed
around
the
variable
capacitor
gang
to
reduce
variations
of
capacitance
between
the
rotor
and
ground.
R27,
C24,
and R37,
C30
are
frequency
roll-off elements
to
maintain
stability
and
diode,
03,
provides signal
continuity
and
circuit
stability
when
TR6
cuts
off
during
the
period
before
the
termistor
reaches
operating
temp-
erature
and
thus
reduces
output
signal level
to
normal.
The
full
output
of
the
oscillator
from
the
emitter
of
TR6,
is
applied
through
R9
and
C8
to
amplitude
control,
R10, and
thence
to
the
Power
Amplifier. A
tap
on
the
load resistor
of
TA6
supplies a lower level signal
to
the
input
of
the
Squaring
circuit,
A46 provides
extra
current
to
TR6
to
assist
"pull-up".
The
entire
oscillator
is
mounted
in
a screen
box
to
minimise
hum
and
noise pick-up.
Thermistor
R47
compensates
for
amplitude
changes
in
the
oscillator with
temperature.
'
Section
41
4.2
POWER
AMPLIFIER
The
power
amplifier
of
the
J3A
is
fed
from
a regulated rail
of
+37V and consists
of
transistors,
TR101
-TR 106.
TR101
and
TR102
are
connected
in
a
'long
tail'
configuration
the
input
signal from
the
amplitude
control,
R10, being
applied to
TR101
and
the
negative feedback
to
TR102.
The
base
of
TR101
is
biased at
1/4
rail voltage via
R104
and
R102, and
the
input
signal
is
a.c.
coupled
through
002.
The signal path through
the
Amplifier
is
from
the
collector
of
TR101
through
emitter
follower,
TR103,
and
the
common·emitter
stage,
TR
104,
to
the
complementary
output
pair,
TR105
and
TR106.
There are
two
negative feedback paths
to
the
base
of
TR
102, via equal resistors, R
108
and R120. R
120
is
connected
directly
to
the
output,
and R
108
is
returned
to
a feedback winding
on
the
output
transfo'rmer.
As
this
is
effectively
'grounded'
for d.c., stability
is
reached when
the
mean
output
voltage
is
twice
the
base voltage
of
TR102,
that
i9
half
the
rail voltage, enabling
the
Class B
output
transistors,
TR105
and
TR106,
to
swing equally
in
both
directions.
For
signal currents,
R108
and
R120
are
in
parallel, since
the
feedback winding has
turns
equal
to
the
primary
of
the
output
transformer.
The
negative feedback signal
through
these resistors develops a voltage across R
11
O+R
111, which
defines
the
voltage gain
of
the
Power Amplifier. Bypass
capacitor.
C106,
is
large
enough
not
to
affect
the
feedback
at
the
lowest
frequency.
Quiescent
current
for
the
output
transistors, TR
105
and
TR106,
is
controlled
by
transistor
TR108
which,
together
with diodes
0103
and
0104,
is
in
intimate
contact
with
the
heat
sink
on
which
the
output
pair are
mounted.
When
the
heat
sink
temperature
begins
to
rise,
TR108
also heats
up'
and
as
its base-
emitter
voltage
is
fixed, it draws increasing
emitter-collec~or
current,
thus
diverting bias
current
away
from
the
oUtput
transistors
and restoring equilibrium.
To
increase
the
gain
of
inverting stage, TR 104, and
to
assist
'pull-down',
the
load
of
TR
104
is
bootstrapped
to
the
output
of
the
amplifier. A
tap
on
the
bootstrap
through
resistors, R
116
and
R
117,
provides a voltage
approximately
equal
to
the
negative feedback
at
TR102
base, and
to
this
is
returned
the
common
emitter
resistance
of
the
i~put
pair,
TR101
and
TR102.
As
in
the
oscillator, this
technique
reduces
distortion
by
maintaining
constant
signal
current
in
the
long tailed pair.
R109 and C104, R107 and C105,
R118
and C112, and C113
are
frequency
roll-off
components
to
maintain
stability.
Bypassed resistance, A112, limits
switch·dn
surge
currents
in
the
amplifier, and
0102
prevents
hard
bottoming
of
TR104,
which
could
occur
while
the
oscillator
amplitude
is
settling.
The
input
to
the
amplifier
is
taken
via R101
to
a
socket
at
the
back
of
the
instrument,
thus
providing
the
low
distortion
amplitude
controlled
signal
directly
from
the
oscillator. An
external
signal
can
be
infected
at
this
point
also,
to
mix resistively
with
the
oscillator
waveform,
be
amplified and
become
available
at
the
power
output
of
the
J
3A.
The
injected
signal
must
be
within
the
frequency
range
of
t::he
output
transformer
in
circuit
at
any
one
time.
a
Circuit
Description
4.3 POWER
OUTPUTS
The
output
of
the
Power
Amplifier
is
coupled
through
C
116
and a
section
of
the
Frequency
Swrtch
of
the
J3A,
to
the,
primary
of
Tl
or
T2. These are
the
Low
Frequency
and .
High
Frequency
output
Transformers
and
operate
respectively
from
10Hz
--10kHzand
10kHz-
100kHz.
Their
feedback
and
secondary
winding
are
also
switched
by
the
Frequency
Switch
as
range
is
changed.
(i)
LOW -Z
OUTPUT
A
tapping
on
the
primary
of
each
output
transformer
provides
3V
r.m.s.,
e.m.f.,
between
ground
and
the
Low
-Z
terminal.
The
source
impedance
is
approximately
1 n
permittrng
about
1
Watt
to
be
delivered
into
a
load
of
5
Ohms.
The
maximum
available
current
IS
approximately
0.9A
r.m.s.
Iii)
300·0·300
Ohm
OUTPUT
Bifilar
wound
seconrlaries
on
each
transform~r
supply
2 x
15V
r.m.s.,
e.m.f.
to
the
balanced
output
termtnal!l
through
balanced
attenuators
of
20
and
40dB.
Separate
resistors
are
brought
in
by
the
Frequency
Switch
to
pad
the
secondaries
of
both
transformers
to
300
Ohms
each.
The
respective
centre-taps
are
alsu
switched
and
the
outputs
are
thoroughly
screened
(iii) A
protection
circuit
will
cause
the
J3A
to 'Cycle"
on·uff
this
condition
being
visible
on
the
output
meter
if
an
attempt
is
made
to
draw
excess
power
from
the
instru·
ment.
In
view
of
its
low
output
resistance
excess
power
is
almost
invanably
drawn
from
the
Low-Z
output
by
a
short
circuit.
The
protection
circuit
will be
explained
in
the
section
dealing
with
the
Power
Supply.
(See
reference
to
peak
current
limiting
l.
4.4
SQUARE
WAVE
OUTPUT
As has
already
been
mentioned,
a
tap
on
the
load
res1stot
of
thtt
output
at
the
Wien
Bridge
Oscillator
supplies
the 1nput
signal
to
the
Squarer.
Emitter
follower.
TR
131,
further
isolates
the
Oscillator
from
the
Squarer
to
min1m1se
inter
action.
The
output
from
TR
131
·,s
coupled
through
C132 to the
base
of
TR132,
which, With
TR133
forms a
Schmitt
trigger
circuit
in wh1ch
the
long-tail
current
through
A
134
is
switched
on-off
at
the
collector
of
TR
133.
The
output
level
is
controlled
by
potentiometer.
A
142.
and
taken
to
the
output
terminal
\lia
R139.
C133
is
a
speed·up
capacitor
to
the
base
of
TR133
and
preset
trimpot,
A136,
sets
the
mark-space
ratio.
R143
is
selected
on
testm
parallel
with
R
142
to
adjust
the
output
level
to
be
between
+SV
and
+5.5V.
The
Squarer
is
supplied
through
buffer
emitter-follower,
TR134,
and Zener
base
reference,
0131,
to
isolete the fast
transients
from
other
peru
of
the
J3A.
The
same
Zener
0131
after
filtering
serves
as
the
reference
for
the
Power
Supply.
'
Section
4
4.5
POWER SUPPLY
Long-tailed
pair,
TR
161
and
TR162,
compare
the
Zener
reference
to
a
fraction
of
the
d.c.
output
voltage
at
the
slider
of
trimpot,
R
162.
The
collector
of
TR161
conventionally
drives
compounded
series
output
emitter
followers,
TR
164
and
TR
165,
the
latter
being
the
main
series
regulator
connected
to
a
heat
sink.
Zener
diode
0162
applies
bootstrap
feedback
from
the
emitter
of
TR165
to
R168,
the
collector
load
of
TR161/TR163.
thus
presenting
a
high
impedance
load
and
Increasing
the
loop
gain.
R169
and
C164
are
frequency
roll-off
stability
components.
The
input
to
the
P.S.
is
provided
by
the
secondary
of
mains
transformer.
T3,
and
Bridge
Rectifier,
BR
161,
feeding
Reservotr
capacitor.
C
166.
whose
negative
terminal
is
taken
to
the
0-volt
(ground)
line
through
1
Ohm,
A170.
The
protectton
ctrcuit
referred
to
under
Section
4.3
(iii)
is
composed
of
R
164,
a
2.2
Ohm
resistor
b'etweer.
TR
165
and
the
P.S.
output.
tranststor,
TR163;
R170;
trimpot,
A165,
and
C163.
TR163
is
connected
so
that
its
base-emitter
monitors
rhe d c.
voltage
drop
1n
R164,
its
collector
being
1n
comrr10n w1th
that
of
control
transistor,
TA161.
Hence,
d a
current
ot
more
th;:tn
approximately
250mA
is
taken
through
R
164,
TR
163
will
conduct
and
reduce
the
base
current
av<1dahle
to
the
senes
control
transistor.
This
convent1unal
current
senstng
and
limtting
alone,
would
also
l1m1t
the
poslttve
current
peaks
of
the
output
waveform,
especially
at
the
lower
lrequencies.
While
the
current
overlo<Jd
stmsor,
TR163,
is
arranged
so
that
its
base
1s
d.c.
htased
hy
potential
across
R164,
the
a.c.
component
is
llnlanced
out
in
trimpot,
R166,
with
a
fraction
of
the
opposing
~1gnol
voltage
generated
across
R
170
and
a.c.
coupled
VIJ
C163.1ncreasing
mean
current
in
R164
causes
TR163
to
conduct.
l1m1t1ng
the
drive
to
TR164
and
TR166,
ttlus
dropptng
tt1e
output
voltage.
C163
then,
however,
dtscharges
through
R
178
into
the
base
of
I R
163,
thus
collaps1ng
thP.
supply.
In
addition,
the
t1me
constants
arc
suctl
that
wll"'!n
the
supply
collapses
on
overload,
the
Wien
bridge
oscillator
is
stopped
and
waits
until
its
control
thermistor
cools
before
it
can
restart.
The
ebsance
of
signal
effectively
removes
the
overload
from
the
P.S.
which
then
restores
output
The
cycle
of
events
continues
until
thi
overload
is
removed
or
the
signal level
is
turned
down.
Overload
1s
shown
by
the
Output
Level
meter
cycling
on·off
at
approxtmatelv
2
second
tntervals.
A
faster
'cycling'
VISible
on
the
Output
Level
meter
generally
indicates
an
1nternal
fault.
rather
than
excessive
external
loading.
Nutt!
Under
certatn
condittons
of
overload,
the
peak
current
lim1t1ng
c~rcuitry
of
the
output
stage
can
tnl!tate
the
'cycling'
of
the
protection
circuit.
This
Situation
is
most
l1kely
to
arise
when
excessive
magnet1s1ng
current
IS
required
by
the
output
transformer.
etther
because
of
external
d.c.
magnet·
. 1sat1on
or
through
a
fault.
This
initiation
of
cycling
wilt
cause
no
damage
to
the
instrument.
I
1
l
l
I
J
I
I
I
I
I
I
l
I
Circuit
Description
4.6
METER
CIRCUIT
Equal signals
from
the
output
of
the
P.A.
and
ihe
feedback
winc!ing,
supply
the
germanium
diode
full wave bridge
rectifier
through
equal
resistors, R151
and
R
152.
The
resultant
d.c.
is
then
set
and
filtered by R
153,
R
154
and
C151.
The
rectifier
is
essentially average
current,
as
most
of
the
applied voltage
is
dropped
across
the
two
equal
resistors.
By
monitoring
the
two
points
1:hat
supply
the
feedbacK
to
the
Power Amplifier,
the
rrieter
circuit
is
effectively
connected
to
the
'ideal'
transformer
driving
the
balanced
Outputs,
and
thus
compensates
for
transformer
losses.
4.7
MAINS INPUT
Transformer,
T3,
is
conventionally
arranged
with
a series-
parallel
primary
and
has a single well-screened secondary.
The
primary
is
sWitched and fused, and a Neon
indicator
is
fed
from
one
half
primary.
(See 3.1 (i)
and
Fig.
21
4.8
EXTERNAL
D.C. SUPPLY
Two
coded
sockets
at
the
back
of
the
instrument
permit
operation
from
a
FLOATING
D.C. supply
of
40·48V.
Current
at
maximum
output
and
l"oading
is
approx.
250mA.
A
diode,
internally,
protects
against
incorrect
polarity
of
the
external
supply.
Section
4 9
FOR SERVICE MANUALS
CONTACT:
MAURITRON
TECHNICAL
SERVICES
www.mauritron.co.uk
TEL:
0Hl44
· 351694
FAX:
01844-352554
10
Maintenance
5.1
REMOVAL
OF
COVERS
Warning:
Take
care
not
to
touch
the
supply
transformer or
fuse
with
the
supply
ON.
To
remove
the
covers
from
the
instrument,
firstly remove
the
bottom
by
unscrewing
the
4
retaining
screws.
Then
by
gently
pulling
the
side
panels
outwards
the
cover
should
lift
off.
It
will
generally
be
found
more
convenient
to
carry
out
adjustments
or
repairs
with
the
bottom
of
the
instrument
upwards
and
to
use
an
external
supply
(See
48)
for
testing
and
calibration.
5.2
REMOVAL
OF
OSCILLATOR
BOX
COVER
This
is
held
on
by seven screws, 4
at
the
bottom
and 3
at
the
top,
all 7 screws
working
in
slots.
After
undoing
each
screw
by
about
3
turns,
the
cover
can
be
slid
out.
Refitting
is
a reversal
of
the
above
procedure,
being careful
to
butt
the
cover
well
against
the
steel
oscillator
box
when
tightening
the
screws.
5.3
REMOVAL
OF
PRINTED
CIRCUIT
BOARD
ASSEMBLIES
(i) Removal
of
Oscillator
P.C.B. (Fig. 4)
This
is
released
by
undoing
4 screws,
as
shown
in
the
figure.
Then
the
yellow
lead
on
the
underside
of
the
board
to
pin
'C'
(Guard)
is
unsoldered.
The
board
is
now
free
and
can
be
eased
out
and
swivelled
about
the
cables
and
leads
going
to
the
Range
Switch.
(ii) Release
of
Master
P.C.B.
(a)
Remove
4
screws
securing
rear panel. Disconnect
the
2
leads
from
the
Low
Distortion
terminals.
(b)
Undo
the
two
screws
that
hold
the
board
to
the
bracket
near
the
Mains
transformer.
(c)
Disconnect
the
two
brackets
that
support
the
board
to
the
case
(top
and
bottom)
towards
the
middle
of
the
P.C.B.
ld)
Remove
the
top
screw
securing
the
output
transistors'
heat
sink
to
the
side
member,
near
the
two
large
electrolytics
mounted
on
the
board.
Slacken
the
corresponding
bottom
screw
securing
the
heat
sink.
The
board
can
now
be
swivelled
against
the
cables
and
harness
to
remove
damaged
components,
although
many
of
these are accessible
simply
by
removing the
rear panel.
Note:
Complete
removal
of
the
P.C.B.'s requires
disconnection
of
all
leads,
which
should
be clearly labelled
for
correct
reconnection.
5.4
SETTING
UP
OF
WIEN
BRIDGE
OSCILLATOR
(i) Work
which
is
possible
with
cover
removed.
The
cover
should
not
be
removed
unless a fault exists
in
the
oscillator
board.
1.
Turn
Fine
Output
Control
to
minimum.
2.
Disconnect
coax.
lead
from
Point
0
(to
squarer)
3.
Check
incoming
+37V
rail
at
check
position
on
switch,
or
on
master
P.C.B. (red leads). If faulty,
disconnect
the
oscillator
from
+37V
rail and
use
an
external
+37V
supply
rated
at
SOmA
to
supply
the
oscillator.
4.
Connect
an
a.c.
coupled
oscilloscope
(1V/div.,
0.1
mS/div.)
to
'Oscil.
Test
Point'
as
shown
in
Fig. 4
(On
the
middle
switch
wafer
outside
the
oscillator
box).
5.
6.
7.
8.
Section
Set
frequency
to
approximately
3kHz,
and
switch
on.
5
If
there
is
no
fault,
oscillations
should
build
up
die
out,
restart
and
stabilise.
Connect
D.V.M.
or
20k
11
V
Voltmeter,
across C25.
Trim
R22
for a
reading
of
12.5-13V
Examine
the
waveform
on
the
oscill·
oscope
for possible clipping,
etc.
It
should
be
clean.
Trim
R34
for 8v p-p
on
the
oscilloscope.
Restore
wiring
to
normal.
(ii) Work
with
cover in posi'tion:
(In
the
absence
of
a fault, begin
setting
up
here)
Step
7
above
may
be
carried
out
by
connecting
a d.c.
Voltmeter
to
'Oscil.
Test
Point').
'
1.
Connect
the
a.c. high
impedance
Voltmeter
~o
'Oscil.
Test
Point'
replacing
the
oscilloscope.
The
Voltmeter
should
be
calibrated
to
1%
at
2.8V
r.m.s., and have a flat
frequency
response
from
10Hz
to
100kHz,
inclusive
of
the
screened
cable
connector.
2.
Connect
the
Frequency
counter
to
the
Squarer
output.
Set
this
to
a
convenient
level.
3.
Select
the
1-10kHz
Range,
and
set
the
dial
to
1kHz.
Note
the
frequency
on
the
counter.
4.
Trim
R34
for
2.8V
r.m.s.
on
the
Voltmeter
and
tune
towards
the
high
frequency
end
of
scale,
carefully
observing
the
voltmeter
reading.
If
the
Wien bridge
is
trimmed
correctly,
the
reading
should
stay
constant
at
2.8V.
5.
Set
the
dial
to
10kHz
and
trim
C2
and
C3
to
obtain
ten times
the
frequency
noted
in
step
3
above.
Note
that
increasingC2
and/or
C3,
decreases
the
frequency,
and
that
increasing C2
and
decreasing C3,
can
keep
the
frequency
constant
while decreasing
the
output
of
the
oscillator.
The
two
trimmers
should
be
set
for
the
right
frequency
and
least
amplitude
variation
over
the
range.
Note
the
amplitude
at
10kHz.
6.
Reset
1kHz
on
the
counter.
Slacken
the
two
grub
screws
that
hold
the
tuning
gang
spindle
in
the
epicyclic
drive
and
reposition
the
scale
to
agree
with
the
counter.
7.
Set
the
dial
to
1OkHz
and
trim
frequency
to
agree,
with
amplitude
retained
at
that
giving least
variation
over
the
band.
(Step
5.)
8.
Check
frequency/dial
agreement
on
100-lOOOHz
and
10-lOOkHz ranges
at
various
points,
and
if
necessary,
reset
the
dial
(repeating
Steps
6
and
7)
for
minimum
frequency
error
overall. If
the
error
approaches
2%
a
fault
in
the
appropriate
range
resistors
should
be
suspected,
or
else in
the
gang.
9.
Check
10-lOOHz range,
allowing
for
the
+1Hz
tolerance
in
the
specification.
The
oscillator
should
now
be
set
and
be
flat
within
0.3d8.
10.
Finally,
return
to
the
1-10kHz
Range
at
9kHz
setting,
note
frequency
reading
and
'rock'
the
tuning
knob
whilst
adjusting
C2
and
C3
for
minimum
amplitude
bounce.
Check
that
the
noted
frequency
reading
has
been
held
unaltered.
It
should
be
noted
that
clockwise
dial
rotation
producing
amplitude
increase
requires
increase
(frequency
lowering)
of
the
Trimmer
C3
nearest
the
edge
of
the
oscillator
box
(grounded
trimmer).
Conversely,
C2
has
the
opposite
effect.
I
J
1
I
I
I
I
I
1
l
r
\
...
f
!
Maintenance
Note:A piece
of
insulated wire
is
wrapped around the
highest range resistor
R8
shunting
it
by
approx.
1/4pF
This
raises
the
frequency
at
the
top
end
of
the
highest
range
by
1%
approx.,
to
produce
closer
agreement
with
the
scale.
5.5
SETTING
UP
OF
POWER
SUPPLy
Note:
All
trim
potentiometers
on
Master P.C.B. can
be
adjusted
from
the
back
of
the
board
through
suitable holes.
1.
Turn
the
level
control
to
zero.
2.
Adjust
R
162
for
+37V
:t
0.5V
at
pin
+"37V'
carrying
red lead.
3. Provisionally set R165
at
its mid setting.
After
adjusting
the
Power
Amplifier,
the
frequency
is
~
set
to_~z
and
a.c.
coupled
and
float;ng
millivoltmeters
is
connected
between
+37V
pomt
and
the
slider
of
R
165,
to
test
point
marked
"SET
NULL".
The
P.Ashould
be
loaded
with
approximately
5
Ohms
at
the
Low
·Z
tap, the
40dB
attenuator
engaged
to
load
the
balanced
output,
and
the
Level
control
should
then
be
advanced
and
R
165
adjusted,
for
minimum
stgnal
on
the
voltmeter
while
increasing level
to
maximum.
The
adjustment
is
eased
if
the
oscilloscope
Timebase
is
set
to
1
~
s/div.
and
'free
run',
in
which
case
the
3kHz
signal
appear
as a
multiple
trace
whose
width
should
be
reduced
to
a
minimum.
If
the
protection
circuit
operates,
switch
off
and
check
R164
and
R170.
The
minimum
unbalance
signal
is
generally
less
tnan
1 millivolt.
4.
Check
that,
at
the
nominal
mains voltage
for
the
transformer
tap
in use,
the
reading
between
the
collector
of
TR
165
(heat
sink)
and
ground,
is
not
less
than
+44V
under
load
as
in
Step
3
above.
5.6
SETTING
UP
THE
POWER
AMPLIFIER
(i) Quiescent
Current
of
Output
Stage.
1.
Set
the
Level
control
to
zero
and
remove
the
loading
from
the
instrument.
Switch
out
the
attenuator.
2.
Switch
off
and
disconnect
the
link
between
the
collector
of
TR106
and
ground
(Fig. 4) The
link
is
at
the
bottom
rear right
corner
of
the
instrument,
near
a large
electrolytic.
Replace
the
link
by
a
d.c.milli-ammeter(-ve
to
ground)
and
solder
a
capacitor
of
value
0.5
to
1
fJ
F across
the
link
pins.
R129
is
adjusted
to
give a
quiescent
current
in
the
output
pair
of
18-30mA.
It
should
be
noted
that
current
through
R130
modifies
the
behaviour
of
TR108
(see
4.2, oar
a.
4)
so
that
quiescent
current
IS slightly
reduced
with
increased
heat
sink
.temperature,
caused
by
running
at
full
load
over
long
periods.
3.
Switch
off
and
restore
circuit
link.
(ii) Check
the
output
d.c.
devel between
ground
and the
+ve end
of
C114
(See
Fig.
4).
It
should
be
within
1
volt
of
half
the
supply
rail.
If
not,
check
R102
R104, R108,
R120
and
C106
for
leakage.
'
5.7
(i)
Iii)
,iii)
(iv)
(v)
(vi)
5.8
(i)
Section
5n
SETTING
UP
SQUARER
Connect
the
oscilloscope
to
Square
Output,
1V/div..
0.1ms/div.
Select
Range
1-10kHz
and
a
frequency
of
1kHz
so
that
1 cycle
(square)
occupies
exactly
10
oscilla'scope
divisions.
Trim
R
136
for
mark/space
ratio
Of
unity.
Change
the
polarity
of
trigger on
the
oscilloscope
and
retrim,
if
necessary,
so
that
the
transition
of
the
square
wave
occurs
at
the
same
point
on
the
oscilloscope,
near
the
0.5ms
centre
..
This·
should
eleminate
possihle
oscilloscope
nonlinearity.
Verify
that
amplitude
is
within
specification.
If
excessive,
suitably
shunt
front
panel
control
R142
(1
k
ll
)
by
A.O.
T. resistor, R
143
across the pins at
the
output
of
the
squarer
projecting
from
the
track
side
of
the
PCB.
Should
the
outpUt
be
less
than specified, check D131
(24V
Zener),
R142,
R132,
R
133
and R
134,
in this order.
Confirm
that
rise
and
fall
times
are
within
specification.
If
not,
check
R135
and
C133.
DISTORTION
(See
Fig. 3)
lf
the
preceding
adjustments
nave
been
carried
out
correctly,
distortion
should
be well
within
specification
Apart
from
obviously
faulty
circuitrY.
the
following
is
a
short
check
list of
the
more
likely causes of
excessive
distbrtion,
if
the
instrument
is
functioning
in
other
respects. If available, a DistortiOn
Factor
Meter
is
invaluable
in
tracking
down
disto.rtion,
particularly
if possessing an
output
giving residual
component
frequencies
after
cancellation
of
the
fundamental.
1. Change
of
component
parameters
could
cause
short
burst
of
high
frequency
oscillation
at
some
specific
point
of
the
signal
cycle,
as
seen
on
an
oscilloscope,
particularly
immediately
after
switching
on
when
oscil.lator
amplitude·
is
'still
unstablised.
When
the
J3.B
with
this
forni
of
distortion
is
used as a signal
source,
it
will .
generally
result
in
'noisy'
or
flickering
measurements.
2.
3.
4.
5.
Cross-over
distortion
in
the
power
output
stage,
generally
due
to
failure
or
error
in
the
bias
components
(see
section
5.
7 i)
or
damaged
output
transistors.
Supply
hum
or
signal ripple across
th~
37V
rail, caused
by
power
supply
failure
or
damaged
electrolytic,
C115.
At
full
loading, the
total
supply+
signal ripple across
C115,
should
not
exceed
40·50
mV
p-p.
Square
Wave
break-through,
caused
by
failure
of
TR131
or
TR134.
If
the
distor_tion
~gives
predominantly
3rd
harmomc
at
~OkHz~
higher
than
the
value
s~ecifi~d.
with
co·~esP9nding
increases
of
dtstortton
at
lower
t'ri(quencies,
suspect
a
faulty
stabilising
Thermistor
in
the
oscillator.
12
Maintenance
Section
5
(ii)
Any
failure
or
error
in
the
feedback paths (including
Switching)
in
the
P.A.,
or
wrongly
set
protection
and limiting
circuits
in
the
P.S., can cause large
distortion,
increasing
with
output
level.
(iii)
If
the
distortion
increases
with
output
level
beyond
the
specified limits
then
the
fault
is
with
the
P.A.
If
the
fault
is
in
the
oscillator,
then
distortion
is
sensibly
independent
of
level
at
all
outputs.
Fig. 3 Graph
of
Distortion
and Frequency
1
0·
5~
0·
·-"'~
.~~
,.,:.o,C'
'·~
'
"'
.
0
--~&v.
~
2~r~~
'
...
! 0
,,
·1
'
VJ-.
SPECIFICATION
OUTPUTS
1
&.
2
z
0
i=
a:
0
....
</)
2i
..1
0·0
;! 2
0
....
0·01
0·001
10
..•
""'-.
'-..fv,..
'
20QH,
I
·..
--,<>
' SPECIFIED
·..
'·
-·
""'T_"!P.!,C,!L_
O~!P~~!.,
~2-
_ -------------
·..
......
...
...
....
...
_
··
....
~"
....
...
...
__
SPECIFIED ::l\t\
TYPICAL
LO
DISTORTION
OUTPUT
, ,
··~
·-r
-
...
-
...
_
...
_
~,
,,
---
.
.
••
.;<~~
tg
.ft£"
••• •t
,,
II£
•••
••
Dt8
'~&,
··
..
•ulltt
Measuremers
made
at
oujput
level
setttg
of
25V.RMj
'
103
FREQUENCY
Hz
.,...._0/Pl--;...._
,,
,,
-~~;,~-
---·
·~,
...
'••
r
•••••
...
.
..
0:1
P.------
0·05
,
,
,
,,
,
0·03
/
'
'
'
'
-
.
.........
10'
r,
!
1
1
I
I
I
I
I
r
'
,.
..
1
i
'
i
l
Components
List
and
Illustrations
Section
613
ABBREVIATIONS USED
FOR
COMPONENT DESCRIPTIONS
RESISTORS
cc
CF
MO
MF
ww
CP
PCP
CAPACITORS
CE(1)
CE(2)
SM
PF
PS
PE
PC
E
T
Carbon
Composition
Carbon
Film
Metal
Oxide
Metal
Film
Wire
Wound
Control
Potentiometer
Preset
Potentiometer
MPD
PC
Ceramic
Ceramic
Silver Mica
PlastiC Film
Polystyrene
Polyester
Polycarbonate
Electrolytic
(aluminium)
Tantalum
NOTE:
Components
coded
on
the
master
PCB
in
YELLOW
are
not
used.
'
'hW
1/8W
"hW
"4W
6W
500V
10%
5%
2%
1%
5%
20%
20%
+
80%
-
25%
:!:_
10%
:!:_
10%
:!:_
10%
+ 50%
10%
+ 50%
10%
unless otherwise stated
unless otherwise
stated
unless
otherwise
stated
unless
otherwise
stated
unless otherwise stated
unless otherwise stated
unless
otherwise
stated
unless otherwise stated
unless
otherwise
stated
unless otherwise stated
FOR SERVICE MANUALS
CONTACT:
MAURITRON
TECHNICAL
SERVICES
www.mauritron.co.uk
TEL: 01844
··
351694
FAX:
01844-352554
I
14
Components List and Illustrations Section 6
'1'
I
Circuit Ref. Value Description
Tolerance%
Part
No.
l
RESISTORS
R1
30M
MF
+1
32772
R2
3M
MF
:!:_0.5
32773 •
R3
300K
MF
:!:_0.5
32774
R4
30K
MF
:!:_0.5
32775 I
R5
30M
MF
:!:.1
32772
R6
3M
MF
:!:_0.5
32773
R7
300K
MF
:!:_0.5
32774
R8
30K
MF
:!:_0.5
32775 r
R9
270
CF
:!:_5
1/8W
28720
R10
5K
Cp
A4/32606
R11
47K
CF
:!:_5
1/8W
21815
R21
lOOK
CF
:!:_5
1/8W
21819
...
R22
25K
PCP
29602
R23
47K
CF
:!:_5
1/8W
21815 I
R24
1K
CF
:!:_5
1/8W
21799
R25
15K
CF
:!:_5
1/8W
28727
R26
5K6
CF
:!:_5
1/8W
21806
R27
560
CF
+5
1/8W
21798 I
R28
1K8
CF
:t5
1/8W
28725
R29
750
MO
+2 28790
R30
390
MO
:!:_2
26740 I
R31
2K2
CF
+5
1/8W
21802
R32
1K5
MO
:!:.2
26733
R33
820
MO
:!:.2
27346
R34
2K5
CP
28969 I
R35
12K
CF
:!:_5
1/8W
21810
R36 330
CF
+5
1/8W
28721
R37
180
CF
:!:.5
1/8W
21795
R38
1K8
CF
:!:_5
1/8W
28725 I
R39
680
CF
+5
1/8W
28723
R40
lK
CF
:!:_5
1/8W
2f799
R41
33K
CF
:!:_5
1/8W
21814 t
R42
100
CF
:!:_5
1/8W
21794
R43
2K7
CF
:!:_5
1/8W
28726
,.;
R44
1.9V
/1
ma
Wkg.
Thermistor R
15
3mW
SELECTED
32421
R45
330
CF
+5
1/8W
28721
R46
3K9
CF
:!:_5
1/8W
21804
R47
1
K8/25"C
Thermister
RP152CY
1/4W
'-
10% 35712
R101
4K7
CF
:!:_5
1/8W
21805
R
102
33K
CF
+5
1/8W
21814
R103
l
R104
lOOK
CF
:!:_5
1/8W
21819
R
105
6K8
CF
-<:5
1/8W
21807 r
R106
3K3
CF
:!:_5
1/8W
21803
R
107
82
XX
+5
1/BW
28717
R108
16K
MO
:!:.2
1/8W
28!!05
R109
820
CF
:!:_5
28724
R110 330
CF
28721
R
111
2K7
MO
:!:.2
1/8W
26728
R112
8K2
CF
:!:_5
1/8W
21808
R113 68
CF
:!:_5
1/8W
28716 \
R114 330
CF
:!:_5
1/8W
28721
'
l
R115
1'K
CF
+5
1/8W
21799
R116
270
CF
:!:.5
1/8W
28720
'
Components
List and Illustrations Section
615
Circuit Ref. Value Description Tolerance% Part No.
RESISTORS (Con't)
R
117
120
CF
+5
1/BW
28718
R118 56
CF
±_5
28715
R119
1K5
CF1
+5
1/8W
A.O.T.
21801
R120
16K
MO
:;:-2
28805
R
121
1
ww
34200
R122
1
ww
1/8W
34200
R123
330
CF
±_5
28721
R124
2R2
ww
1/8W
31894
R125
R126
R127
470
CF
+5
1/8W
21797
R128 220
CF
±_5
1/2W
18524
R129
1K
PCP
32523
R130
15K
CF
±_5
1/8W
28727
R131
12K
CF
±_5
1/8W
21810
R132
15K
CF
±.5
1/8W
28727
R133
8K2
CF
+5
1/8W
21808
R134
2K7
MO
+5
1/8W
A.O.T.
26728
R135 150
CF
+5
1/8W
28719
R136
2K5
PCP
28969
R137
15K
CF
±.5
1/8W
28727
R138
8K2
CF
±.5
1/8W
21808
R139
470
CF
+5
1/8W
21797
R140
2K2
CF
±.5
1/8W
21802
R141
12K
CF
:':.5
1/8W
21810
R142
1K
CP
A4/32607
R143
CF
±.5
1/8W
A.O.T.
R144
I
FITTED
IN
561
CF
:':.5
1/8W
28715
R145
I
PLACE
OF
2R2
ww
±_5
2%W
31894
R151
I 'SET
10
LINK'.
!OK
CF
±_5
1/8W
21809
R152
!OK
CF
±.5
1/8W
21809
R153
2K5
CP
28969
R154
1K5
CF
±.5
1/8W
21801
R
161
12K
CF
±.5
1/8W
21810
R162
5K
PCP
28970
R163
22K
CF
:':.5
1/8W
21812
R164
2R2
CF
34201
R165
5K
PCP
28970
R166
22K
CF
±.5
1/8W
21812
R
167
2R2
CF
±.5
1/8W
34201
R168
6K8
CF
±.5
1/8W
21807
R169
68
CF
±.5
1/8W
28716
R170
1
ww
34200
R
171
470
CF
±.
1/8W
21797
R174
1-10M
A.O.T.
R178
1K2
CF
±.5
1/8W
21800
R201
1480
MF
+1
32776
R202
15K
MF
+1
32777
R203
1480
MF
+1
32776
R204
15K
MF
±.1
32777
R205
367
MF
±_1
32778
R206
306
MF
±_1
32779
R207
367
MF
±_1
32778
R208 306
MF
±_1
32779
R209
367
MF
±_1
32778
R210
306
Mr-
±.1
32779
R211
367
MF
±.1
32778
R212
306
MF
±_1
32779
'
I
16
Components
List and Illustrations
Section
6 '
'
J
C~rcuit
Ref..
Value Description Tolerance% Part No. l
RESISTORS (Can't)
R221
OR68
CF
:!5
31888
R222 280 MF
_:!:1
32826
R223 280 MF :!1 32826
R224 187 MF
_:!:1
29471 ]
R225 187 MF
_:!:1
29471
CAPACITORS
C1
l
C2
6/25pF
Trimmer 23593 •
C3
6/25pF
Trimmer 23593
C7
518pF C7A +
C7B
33999
+518pF
C8
681'F E
16V
32174 I
r.g 1.5pF
S/M
813
C21
150 F E
16V
32175
C22
0.22~F
PE
250V 35607
C23
681'F E 6.3V 32162 I
C24
68pF
CE(21
:!10
500V
22374·
C25
1000J.~F
E
16V
32178
C26
5.6pF
CElli
500V
22361
C27
1501'F E
16V
32175 I
C28 4701'F E
6.3V
32164
C29
.011'
F
CE(ll
250V 22395
C30 33pF
CE(2~
_:!:10
500V
22370 I
C31
470,F
E
40V
32191
C32 47,.F E
40V
32188
C101
0.22~F
PE
31379
I
C102
221'f
E
25V
32161
C103 5.6pF CE(2) 500V 22361
C104 56pF
CE(21
500V 22373
C105
6BOpF
CE(2)
.:!
10 500V 22385 I
C106 1501'f E 16V 32175
C107 82pF CE(2)
500\'
22375
C108 4701'F E
6.3V
32164
C109 .Ol,.F
CElli
250V
22395
C110 56pF
CEI21
500V
22373
C111
4701'f
E
6.3V
32164
C112 56pF CE(2) 500V 22373 t
C113 5.6pF CE(2)
.500V
22361 i
C114 3301'F E 16V
33998
C115 220011' E
40V
31844
C116 2200f'F E :?5V 32520 r
C117 1001'F E
4V
34994
C131
.1
l'f
CElli
30V
36709
C132 25f'F E 25V 32181
C133
3J,F
E 500V 22370
C134
471'f
E
25V
32182
·-
C135 560 pF
CE
22384
C151
471'F E
10V
32167 i
I
C161
331'f
E L
16V
32173
C162 47uF E
25V
32182
C163 47uF !:
63V
32199 f.'
!
'
Table of contents
