Marconi CR150/6 Manual

DESCRIPTION
&
OPERATING
INSTRUCTIONS
FOR
HF
COMMUNICATIONS
RECEWER
Type
CR.iyo/6
Coc-
7%’
,TCcr
-r
)
—
OFFTCE
‘H1
7
7
—
-
Technical
Handbook
T.2719/2
Marconi
MARCONI’S
WIRELESS
TELEGRAPH
COMPANY
LIMITED
Chelmsford,
Essex. England
Telephone:
Chelmsford
3221
Telex:
1953
Telegrams:
Expanse
Chelnuford
Telex
12058

Printed
in
England
and
Published
by
Marcunis
Wireless
Telegraph
Company
Limited.

I
I
I
I
Receiver Type CR.
i5016
II
a
a
i.e.’
E1
0
a.
S

—
— —
— —
—
—
a
—
a
—
a
—
—

1
INThODUCT1ON
CONTENTS
Page
1
1.
1
General
...
..
.. .
-
I
2.2
Electrical
Characteristics
2.2.1
Circuit Details
2.2.2
Selectivity
2.2.3
Sensitivity
2.2.4
Automatic
Gain
2.2.5
Crystal
Control
2.2.6 Desensitising
2.
2.
7
Metering
2
2
2
2
9
2
3
3
2.3
Tuning
2.
3.
1
2. 3.
2
2.
3.
3
Frequency
Selection
Fine
Tuning
Crystal
Cal
ibntor
3
3
3
3
T
.2719/1
6974
Sensitivity
..
.
Selectivity
. .
.
.
-
Overall
Frequency
Response
Thermal
Stability
Automatic
Gain
Control
Outputs
...
Power Consumption
3.1
Controls
..
.
. ..
...
3.1.
1
Power Supplies
Switch
3.
1.2
Band
Change
Switch
3.1.3 Tuning
Controls
3.1.4
Sensitivity
Control
3.
1.5
Operational
Switch
3.1.6
Gain Controls
3.
1.7
Meter
Switch
. -
.
3.L8
Preset Controls
3.2
Location
of
Components
3
3
3
4
4
4
4
4
6
(i)
2
TECHNICAL
SUMMARY
...
...
.
..
...
.
..
...
... ...
...
1
2.
1
Salient
Features
.
.
.
. .
1
2.1.
1
Types
of
Service
. .
.
.
.
.
.
.
.
.
..
.
. .
. ..
.
..
1
2.1.2
RU’
Input
...
...
...
... ...
...
...
...
2
2.1.3
AF
Output
... ...
...
...
...
...
...
...
2
2.1.4
Tropical
Use
...
..
...
...
..
...
.
..
...
2
2.1.5
Power Supplies
.
..
...
.
..
..
.
...
... ...
2
Control
(AGC)
2.4
Performance
2.4.
1
2.4.2
2.4.3
2.4.4
2.4.
5
2.4.6
2. 4.
7
3
GENERAL
DESCRIPTION
5
5
5
5
5
5
5
:3
6
6

I
CONTENTS
(Contd.)
Page
3.3
Mechanical
Construction
..
.
6
4
CIRCUIT
DESCRIPTION
6
4.
1
General
Arrangement
...
...
...
..
.
...
..
.
6
4.2
Signal
Frequency
Circuits
... ...
.
..
..
...
7
4.3
Intermediate
Frequency
Circuits
...
... ... ...
7
4.4
Third
(Beat)
Oscillator
and
Signal
Detector
...
...
7
4.5
Audio
Frequency
Circuits
...
..
...
. .. ..
.
7
4.6
Automatic
Gain
Control
Circuits
... ... ... ...
7
4.7
Noise
Limiter
...
...
...
...
.
..
...
...
8
4.8
Crystal
Oscillator
..
.
...
..
..
..
...
.
..
.
..
B
4.9
Desensitising
Circuit
... ...
. ..
.
..
.
..
..
.
8
4.
10
supply
Units
... ...
...
... ... ... ...
...
8
5
INSTALLATION
9
5.
1
For
Mains Working
... ... ... ... ... ... ...
...
9
I
5.2
For
Batteries
or
from
other
DC
Source
... ...
...
..
.
9
5.3
Aerial
Input
Connections
..
.
.
..
... ...
...
. ..
...
9
5.4
Outputs
...
..
.
... ...
...
. .
.
... ... ...
10
5.5
Desensitising
Facilities
...
..
.
...
.
..
.........
10
5.6
AGC
Terminals
and
Time
Constant
Adjustment
... ...
..
. ...
10
5.7
Diversity
Connections
.
..
...
... ... ...
.
..
...
10
6
OPERATING
INSThUCTIONS
... ...
11
6.1
General...
.
..
...
..
11
I
6.1.
1
Preliminary
Adjustments
...
...
...
.
..
..
.
11
6.
1.2
Use
of
PASSBAND
Switch
...
..
.
... ...
...
11
6.1.3
Use
of
AGC
...
.
..
.
..
...
.
..
.
.. ..
.
11
6.1.4
Use
of
Gain
Controls
...
..
.
...
..
...
12
6.1.5
Use
of
Calibration
..
.
..
..
..
... ...
12
6.1.6
Use
of
Meter
as
Tuning
Indicator
... ... ...
12
6.
1.
7
Use
of
Noise
Limiter
.
.
.
.
.
.
.
. .
...
12
6.1.8
Use
of
Logging
Scale
...
.
.
.
..
.
...
.
..
12
6.1.9
Use
of
Crystal
Controlled
First
Oscillator
.
.. ..
.
13
6.
1.
10
Adjustment
of
Third
Oscillator
...
...
...
...
13
6.1.11
Warming
Up
...
...
...
...
...
...
.
.. ...
14
7
MAINTENANCE
...
14
I
7.
1
General
...
..
.
..
.
..
.
...
...
.
..
14
7.2 Routine
Maintenance
.
..
...
..
.
...
.
-.
14
7.
2.
1
Valve
Replacements
.
.
.
. .
.
..
.
.
.
..
.
.
.
.
14
7.2.2
Replacing
the
Calibration
Drum Drive
Cord
... ...
...
15
7.2.3
Replacing
the Pointer
Drive
Cord
.
..
..
.
...
...
16
1
7.3
Circuit
Checks
...
... ...
...
...
,..
16
7.4
Voltages
and
Feeds
..
.
.
..
...
..
.
.
.
.
..
.
16
6914
(ii)
I
I

CONTENTS
(Contd.)
Page
7.4.
1
Power
Consumption
.
..
17
7.4.2
Voltages
. .
..
.
17
7.4.3
Valve
Feeds
..
.
17
7. 4. 3.
1
Metered Feeds
17
7.4.3.2
Feeds
to
V7
and
18
7.4.3.3
Feed
to
V9
18
7. 4.
3.
4
Current
through
19
7.5
Receiver
Alignment
. ..
7. 5.
1
Test
Equipment
7.5.2
AF
Amplifier
Tests
7.5.2.
1
Sensitivity
7.5.2.2
AF
Amplifier
Tests
7.5.3
Alignment
of
465
ftc/s
IF
Amplifier
Circuits
7.5.3.
1
General
7.5.3.2
Controls
..
.
7.5.3.3
Tuning
IFT.4,
IFT.5 and
IFT
6
(without
Alignment
oscilloscope)
7.5.3.4
Tuning
IFT.
4,
IFT.
5
and
IFT
6
(with
alignment
oscilloscope)
7.5.3.5
Third
Oscillator,
Tuning and
Output
Voltage
7.5.3.6
Tuning
IFT.2
and
IPT.3
(without alignment
oscilloscope)
7.5.3.7
Tuning
IFT.2
and
IFT.3
(with
alignment
oscilloscope)
7.5.3.8
Capacitance
Trimmers
C47,
C124,
C57
and
C126
7.5.3.9
Retuning
IFtG
(after
using
alignment
oscilloscope)
23
V8
...
...
Stabijiser
Tube
V14
...
19
19
19
20
20
20
20
20
20
21
22
22
23
23
7.5.4
Second
Oscillator,
Tuning
and
Output
Voltage
...
...
23
7.5.5
Selectivity
of
405
ftc/s
IF
Amplifier
. .
.
...
.
..
...
24
7.5.6
Stage
Gains of
465
ftc/s
IF
Amplifier
... ...
.
..
. ..
24
7.5.7
Variation
of
Gain
with
Bandwidth
. ..
...
..
.
..
.
25
7.5.8
1600 ftc/s
IF
Amplifier
....
..
. .
.
. ..
..
.
.
..
25
7.
5.
8.
1
IF.
1
Response
. ..
...
.
..
.
. .
..
.
. .
.
26
7.
5. 8.
2
Retuning
IFT.
I
.
. -
. ..
...
..
.
... ...
26
7.5.8.3
IF.l Gain
...
...
...
...
... ...
...
26
7.5.9
Signal
Frequency
Amplifier
... ...
.
..
..
.. ..
27
7.5.9.1
First
Oscillator
Alignment
.
.
.......
. ..
27
7.5.9.2
Alignment
of
Signal
Frequency
Circuits
... ...
27
7.5.
10
First
Oscillator
Voltages
..
..
.
.
.
..
..
.
.
..
28
7.5.
10.1
Variable
LC
Oscillator
.
. .
...
. ...
..
28
7.5.10.2
Crystal
Oscillator
...
...
...
... ...
28
7.
5. 10.
3
External
Oscillator
. .
.
...
.
.
... ...
29
7.6
Overall
Performance
...
...
.
. .
.
..
...
..
.
..
..
.
29
7.6.
1
CIV
Sensitivity
...
..
.
. .
.
..
.
..
.
..
.
. .
.
29
T.2719/1
7.6.2
sensitivity
for
Modulated
Signals
...
. ..
. ....
29
6974
7.6.3
AGC
. ..
... ...
...
... ...
..
... ...
30
(iii)

I
CONTENTS
(Contd.)
Page
7.6.4
Image
Protection
.
..
.
..
... ...
30
7.7
Additional
Performance
Data
...
... ...
30
7.7.
1
Stage
Gains
of
Siia1
Frequency
Amplifier
... ...
.
..
30
7.7.2
Selectivity
of
SF
Amplifier
...
...
..
.
...
.
..
31
7.7.3
SF
Amplifier
Detune
Ratios
...
... ...
.
..
...
31
7.8
Supply
Unit
..
.
... ...
.
..
..
.
32
8
USEYUL
AUXILIARY
EQUIPMENT
... ... ... ...
32
9
COMPONENTS
AND
SPARF
33
I
9.
1
Main
Items
..
.
..
..
. .
...
..
.
..
.....
.. ..
.
33
9.2
Accessories
.
..
..
.
..
.
...
..
.
... ...
.
..
.
..
33
9.3
Components
Lists
. ..
...
...
...
.
..
..
.
.
..
...
33
Receiver
Type
CR15016
No.1
35
Supply
Units
1325/4
and
1325/5
No.2
47
LIST
OF
ILLUSTRATIONS
Photographs
Number
Frontispiece
29512
Fig.
1
MISCELLANEOUS
Block
Diagram
(WZ.
10602/B
Sh.
1)
Fig.
2
Logging
Scale
(WZ.
10953/C
Sh.
1)
Pig.
3
I
Method
of
Fixing
Aerial
Feeder
Cable
to
Plug
042.5328/B
Sh.
1)
Fig.
4
Cord
Drive
Assembly
(I1SK.13976
Sh.1)
Fig.
5
I
CIRCUIT
DIAGRAM
AND
COMPONENT LAYOUT
DIAGRAMS
Circuit
Diagram
of Receiver
(WZ.8394/D
Sh.
1)
Fig.
6
Conponent
Layout
of
Receiver
(WZ.
8395/D
Sb.
1)
Fig.
7
Circuit
Diagram
of
Supply
Unit
(W14768/B
Sh.1)
Fig.
8
Component
Layout
of
Supply
Unit
(WI
10728/B
Sb.
1)
Fig.
9
PERFORMANCE
CURVES
IF
Response
(Y2.
10604/B
Sh.1)
Fig.
10
I
A?
Response
(WI
10606/B
Sb.
1) Fig.
11
Overall
Frequency
Response
04110607/B
Sh.1)
Fig.
12
AGC
Characteristic
042.10605/B
Sh.1)
Fig.
13
Frequency
Drift
(WZ.10603/B
Sh.1)
Fig.
14
Electric
Shock
Treatment
(WZ.
12308/B
Sb.
1)
T.
27
19/
(iv)
I
I

DESCRIPTION
&
OPERATING
INSTRUCTIONS
FOR
HF
COMMUNICATIONS
RECEIVER
TYPE
CR.150/6
I
INTRODUCTION
1.
1
GENERAL
The
CR150/s
receiver
shobfll
in
the
Frontispiece
(Fig.i)
is
a
modified
version
of
the
CR15013
and
covers
the
range
2
to
32
Mc/s
in
four
bands. The
receiver is
a
double-superheterodyne
enploying
intermediate frequencies
of
1600
kc/s
and
465
kc/s.
A crystal-controlled
first
oscillator
operating
on
six
spot
frequencies
is
incorporated
in
addition
to
the
varialfle
LC-controlled
oscillator.
Four
pass-bands
of
1,
3,
8
and
13
Icc/s
are
provided.
All
valves
used
in
the
receiver
are
British
Services
preferred
types. There
are
three
models
of
the
CR150/6
receiver;
glition
A
for
table
mounting
is
shown
in
the
Frontispiece
(Fig.I);
Edition
B
is similar
but
is
suitable
for
rack
mounting,
and
Edition
C
which
is
supplied
without
a
cover
and
is
intended
for
mounting in
a cabinet.
To
reduce
temperature
changes
in
the
receiver,
the
power
supply
unit
is
contained
in
a
separate case
which
may
be
placed
beside
the
receiver
or
in
any
other
convenient
position.
There
are
two
similar
types
of
Supply
Unit;
the
Type
1325/4
for
table
mounting
and
the
Type
1325/5
for
Rack
or
Cabinet
mounting.
Electrically,
the
receivers
are
identical
and
so
are
the
Supply
Units. The
dimensions
and
weights
of the
receiver
and
supply
unit
are
given
in
Table
1.
TABLE
1
unit
Width Depth
Height
Weight
Receiver
Unit
Type
CR150/s
20.
Sin.
17in.
14
in.
16
lb.
(52
cm)
(43
cm)
(35,
6cm)
(28kg)
Swply
Units
Type
1325/4
5.
25in.
lSin.
12
in.
25
lb.
(13.3
cm)
(38
cm)
(30,5cm)
(11.
3kg)
2
TECHNICAL
SUMMARY
2. 1
SaIENT
FEATURES
2.1.
1
Types
of
Service
The
receiver is
designed
for
the
reception of
LW,
MCW
or
telephony
transmissions
and
covers
the
range
2
Me/s
to
32
Mo/s
(150
to
9.4
metres) in
four
bands.
If
desired,
diversity
reception
may
be
employed by
using
two
or
more
receivers.
For
this
purpose,
T.271911
connections
are provided
on
the
receiver
for
an
external common
oscillator
and
for
a
69’74
conron
automatic gain
control
circuit.
1

I
2.1.2
HF Input
The
aerial
may
be
connected
directly
to the
receiver
or
via
a
75-
100 ohm
balanced
or
unbalanced
feeder.
2.1.3
Ar
Output
Output
connections
for
a
3 ohm
loudspeaker,
high
or
low
resistance
phones
and
a
600
ohm
line
are
provided.
2.1.4
Tropical
Use
The
receiver
is
suitable
for
continuous
operation
under
tropical
conditions.
2.1.5
Power
Supplies
The
receiver
supply
unit
Type
1325/4
or
1325/5
will
operate
from
a
single-phase
50-60
c/s
AC source
of
200
to
250
volts,
or
the
receiver
alone
may
be
operated
from
batteries.
I
2.2
ELECTRICAL
CHARACTERISTICS
2.2.1
Circuit Details
The
receiver
employs
a
double
superheterodyne
circuit
with
a
first
IFof
1600
kc/s
and
second
IF
of
465
kc/s.
Two
signal
frequency
amplifiers
and
an
amplifier
at
the
first
IF
are
followed
by
three
amplifiers
at
the
second
IF
incorporating
the
main
selective
circuits.
The
detector
is
followed
by
a noise
limiter
and
two
stages
of
audio-frequency
amplification.
A block
diagram
is given
in Fig.
2.
2.2.2
Selectivity
High
discrimination
against
adjacent
channel
interference
is
obtained
by
the
use
of
band-pass
crystal
filters
at
465
1cc/s.
Four
pass-bands
of
1,
3,
8
and
13
kc/s
are
provided
so
that
the
selectivity
may
be
adjusted
to
suit
the
conditions
of
service.
High
discrimination
against
image
response
is obtained
by
using
a
relatively
high
first
intermediate
frequency
(1600
kc/s).
2.2.3
Sensitivity
The
sensitivity
is
good
on
all
ranges
and
is limited
only
by
the noise
level
inherent
in
the
first
RF
stage.
2.2.4
Automatic
Gain
Control
(AGC)
The
automatic
gain
control
circuits
enable
wide
fluctuations
of
signal
strength
to
be
tolerated;
alternative
time
constants
are
provided
to
suit
the
type
of signal
being
received.
2.2.5
Crystal
Control
T. 2719/r
The
first
oscillator
may
be
crystal-controlled
on
any
six
spot
frequencies.
6974
2
E

2.2.6
Desensitising
A
desensitising
circuit
enables
the
receiver to
be
fully
or
partially
muted
during
transmission.
2.2-7
Metering
A
meter,
in
conjunction
with
a
selector
switch,
may
be
used
to
measure
anode
feeds
or
act
as
a
tuning
indicator.
2.3
TUNING
2.3.1
Frequency
Selection
A
single
tuning
control
with
fast
or
slow
motion
is
employed
and
provides
continuous
coverage
of
each
frequency
hand.
The
main
tuning
scale
is
calibrated
directly
in
signal
frequencies
and
there
is
also
an
auxiliary
logging-scale
with
high
discrimination.
Ml
receivers
are
individually
calibrated.
2.3.2
FIne
Tuning
A
fine-tuning
control
operating
on
the
second
local
oscillator
covers
the
range
±4
Icc/s
at
all
signal
frequencies.
2.3.3
Crystal
Calibrator
A
crystal-controlled
calibrator
oscillator
is
incorporated
in
the
receiver.
This
oscillator
provides
check
frequencies
at
intervals
of
500
kc/s
so
that
the
frequency
calibration
of
the
main
tuning
scale
may
be
checked;
also,
by
interpolating
on
the logging
scale
between
two
check
frequencies,
the
receiver
may
be
tuned
exactly
to
any
desired
frequency.
2.4
PERFORMANCE
2.4.1 Sensitivity
The
receiver
sensitivity
is
expressed
in
Table
2
as
the
input
voltage
in
series
with
75
ohms
required
to
give
a
20db
signal-to-noise
ratio
on
an
unmodulated
signal,
or
a
10db
signal-to-noise
ratio
on
a
signal
modulated
40%
at
400
c/s.
The
passband
switch
is
set
at
8
kc/s.
TABIJE 2
Wave
I
Frequency
Range
Sensitivity
Image
Siynal
Frequency
Drift
I
Noise
per hour,
less
Band
in
Nc/s
(cTh
rel.
v)
Protection
than.
Factor.
1
2to4
+ato+Sdb 110-90db
0.01%
+Sto+Sdb
2
4
to
8
-i-S
to+5db
110
-
90db
I
0.01%
+3
to
+5db
3 8tolG
to+5db 100-
70db
0.01%
+5to+Sdb
4 16
to
32
+5
to
+9db
85
-
50db
0.02%
+5
to
+9db
2.4.2
Selectivity
T.2719/I
.
6914
The
amount
by
which
the
image
signal
is
attenuated
is
shown
in
column 4
of
Table
2.
3

The
adjacent-channel
selectivity expressed
as
bandwidth
at
6db
and
40db
attenu
ation
is
shown
in
Table
3.
IF
response
curves
are
shown
in
Fig.
10
(WZ.
10604/B
Sb.
1).
I
I
rassband
switch
Bandwidth
in c/s
set
at
—6db
—110db
I
kc/s
1000
4000
3
kc/s
3000 8500
8
Re/s
8000 18000
13
kc/s
13000
30000
I
2.4.3
Fidelity
I
The
overall
frequency
response curves
for
the
8
Re/s
and
13
kc/s
passbands
are
shown
in
Fig.12
(WZ.10607/B
Sh.1).
Response
curve
for
the
audio frequency
stages
is
shown
in
Fig.11
(Wz.10606/B
Sh.l).
2.4.5
Automatic
Gain
Control
The
output
of the
receiver
does
not
increase
by
more
than
10db
when
the
input
signal
is
increased
to
60db
above
the
levels specified
in
column
2
(Sensitivity)
of
Table
2.
The
AGC
tine
constant nay
be
selected
to
suit
the type
of
signal
being
received.
I
I
I
2.4.6
outputs
I
The
receiver
provides three
separate
outputs
as
follows:
imV
to
high
or
low
resistance
headphones.
20mw
to
600
ohm
line.
lOOmW
to
3
ohm
loudspeaker.
2.4.7
Power
Consumption
Mains
operation:
Battery
operation:
4
I
TABLE
3
I
I
2.4.4
Thermal
Stability
The
frequency
drift
at
any
signal
frequency
up
to
30
Me/s
is less
than
5
kc/s
per
hour
after
30
minutes
from
switching
on.
I
I
60
watts
(approximately)
65cM
at
280V;
3.
7.4
at
6.
3V.
I
T.
2719/LU
6974
I
I

3
GENERAL
DESCRIPTION
3.
1
CONTROLS
The
receiver
controls are
as
follows:
3.1.1
Power
Supply
S.itch
The
power
supplies
for
the
receiver
are
normally
switched
on
or
off
by
the
MAINS
switch
on
the
Supply
Unit
Type
1325/4
or
1325/5.
3.1.2
Band
Change
Switch
Any
one
of
the
four
bands
nay
be
selected by
the
band
change
switch
on
the
front
of
the
receiver
(SWA
in
4Z.
8395/fl
Sh.1).
\Then
this
switch
is
operated
the
appropriate
frequency
scale
is
automatically
displayed
on
the
calibrated
drum.
3.1.3
Tuning
Controls
Each
receiver is individually
calibrated
during
factory
tests;
the
main
tuning
scale
is
calibrated
to
show
the
frequency
directly
in
Mc/s.
The
main
tuning
control
rotates the
ganged
variable capacitors
0119
-
0122,
moves
the
pointer
across
the
frequency
scale and
rotates
the
logging
scale
discs,
The
logging
scale has
an
equivalent
length
of
18
feet
and
its
1250
divisions
nay
be
read
to
one
quarter
division.
At
20
Mc/s
one
scale
division
corresponds
to
a
12
ftc/s
change
of
frequency.
The
fine
tuning
control
operates on
the
second
oscillator
and
enables a
change
of
frequency of
up
to
±4
kc/s
to
be
made
at
any
frequency in
the
range.
The
control
is
normally
set
to
centre
zero.
3.1.4
Selectivity
Control
The
PASS-BAND switch
introduces
crystal or
LC
filters into
the
IF
circuits
and
enables
pass-bands
of
1,
3,
8
or
13
ftc/s
to
be
selected.
3.1.5
Operational
Switch
This
switch
has
four
separate functions:
-
(a)
Switches the
AGC
on
or
off.
(b)
Switches the
third
oscillator
on
for
OW
reception.
(c)
Switches on
the
calibration
checking
oscillator
when
required.
(d)
Switches off
the
noise
limiter in
position
2.
3.1.6
Gain
Controls
The
I-IF’
GAIN
control
rotates the
ganged
potentioneters
RV94
and
RV93
in
the
cathode
circuits of
the
1W
and
IF’
stages.
T.2719/1
The
AF
GAIN
control
rotates
the
potentiometer
RV92
in
the
grid
circuit
of
the
6974
first
AF
amplifier Vi.
5

I
3.1.7
Meter Switch
This
switch
enables
individual
valve
feeds
to
be
checked
as
described
in
Section
7.4.3.
The
meter
may
also
be
used
as
a
tuning
indicator.
3.1.8
Preset
Controls
Access
to
the
receiver
desensitising
control
may
be
obtained
by
moving
to
one
side
the small
cover
plate
on
the
front
panel.
The
adjustment
of
this
and
other
preset
controls,
including
the
signal-indicator
zero
setting
and
the
third
oscillator
frequency,
is
described
in
Section
6.
3.2
LOCATION
OF COMPONENTS
The
position
of
each
component
in
the
receiver
is
shown
in
WZ.8395/D
Sh.1.
A
label
attached
to
the
inside
of the
hinged
cover
lists
the valve
types
and
their
positions
in
the
receiver.
I
3.3
MECHANICAL
CONSTRUCTION
The
receiver
components
are
mounted
on
a
chassis
which
is
housed
in
a
steel
case
I
with
a
hinged
lid
so
that
valves
and
crystals
may
be
changed
and
internal
adjustments
may
be
made
without
removing
the
chassis
from
its
case.
To
withdraw
the
receiver
for
servicing
it
is
necessary
only
to
remove
four
screws
from
the
front
panel.
I
The
receiver
chassis
isof
the
inverted tray
type
with
the
valves,
IFtransformers,
main
tuning
capacitors
and
certain
other
components
mounted
on
the
upper
deck
and
the
control
switches,
fixed
capacitors
and
resistors
mounted
underneath
the
deck.
The
RF
circuits
are
included
in
a
sub-assembly
which
is
insulated
from
the
main chassis
to
reduce
the
possibilityof
coupling
between
the
signal-frequency
circuits
asd
the
second
and
third
oscillators.
4
CIRCUIT
DESCRIPTION
4.1
GENERAL
ARRANGEMENT
A
block
diagram
of
the
receiver
is
shown
in
Fig.
2
(WZ.
10602/B
Sh.
1)
and
the
I
circuit
diagram
is
given
in
Fig.6
(WZ.8394/0
Sh.l).
The
receiver
employs
two
stages
of
signal
frequency
amplification
followed
by
a
heptode
mixer
with separate
first
frequency-change
oscillator.
The
first
intermediate
frequency
is
1600
kc/s
and
the
first
mixer
is
coupled
directly
to
the
second
mixer
via
a
pair
of
coupled
circuits
tuned to
this
frequency.
The
second
mixer
is
a
heptode
with
separate-
second
frequency
change oscillator;
the
output
at
the
second
intermediate
frequency
of
465
kc/s which
is
passed
through
a
two-stage
amplifier
incorporating
the
nain selective
circuits
and
bandpass
crystal
filters.
The
465
kc/s
IF
output
is
rectified
by
the
two
diodes
of
a
double-diode
triode;
one
diode
provides
an
audio
frequency
output
while
the
Output
fron
the
other
is
used
for
AGC.
The
triode
section
of
this
valve functions
as
the
first
audio
frequency
amplifier
and
is
followed
bya
triode
output
stage.
The
beat oscillator
T2
/1
is
coupled
to
the
signal
diode.
U
L
I

4.2
SIGNAL
FREQUENCY
CIRCUITS
The
aerial
input
is
taken
to
two
coaxial sockets
which
are
connected
to
the
low
impedance
winding
of
the
first
RF
transformer.
The
signal
frequency
circuits
are
designed
to
minimise
the
variation
of gain
with
frequency.
The
first oscillator
assembly
is
robustly constructed
and
has
good
mechanical
and
thermal
stability;
this
oscillator
may
be
crystal-controlled
for
reception
on
any
six
selected
frequencies
between
2
Me/s
and
32
Mc/s.
4.3
INTERMEDIATE
FREQUENCY
CIRCUITS
The
first
IF
transformer
is
mounted
on
the
RF
sub-assembly
and
the output
at
1600
kc/s
is
passed
to
the
second
mixer
valve
on
the
main
receiver
chassis. The
second
mixer
is
a
heptode
with
a
separate
oscillator
operating
at
a
frequency
of
1135
1cc/s.
This
oscillator
is
provided
with
aFINE
TUNING
control
on
the
front
panel
which
enables
a
change
of
4 1cc/s
to
be
made
on
each
side
of the
centre
zero
so
that
the
receiver
may
be
tuned
across
the
selectivity
curve of
the
signal
frequency
and
first
intermediate
frequency
circuits;
these
circuits
are
designed
so
that
mistuning
by
the
FINE
TUNING
control
does
not
cause
more
than
one
decibel of
asymmetry
at
the
worst
point.
The
second
IF
amplifier
(465
kc/s)
controls
the
overall
selectivity
of
the
receiver;
the
two
widest
passbands
are
determined
by
variation
of
coupling between
two
pairs
of
tuned
circuits.
One
double
crystal
filter
is
introduced
for
the
3000
c/s
passband and
a
second
double
crystal
filter
reduces
the
passband
to
1000
c/s.
4.4
THIRD
(BEAT)
OSCILLATOR
AND
SIGNAL DETECTOR
The
beat
oscillator
V13
is
capacitance-coupled
to
the
signal
diode
V7a
which
is
supplied
with
the
second
IF
at
465
kc/s
from
the
secondary
of
the
last
intermediate
frequency
tramsforner
Irr6.
The
amplitude
of
the
heat
oscillator
voltage
is
such
that,
although
it
will
fully
modulate
the
strongest signal,
it
will
not
operate
the
automatic
gain
control.
Efficient
screening
is
employed
to
prevent
harmonics
from
the
beat
oscillator
circuits
from
interfering
appreciably
with
the
signal-frequency
input.
4.5
AUDIO
FREQUENCY
CIRCUITS
The
triode
elements
in
VI
function
as
an
audio-frequency
amplifier
which
is
resistance-capacitance
coupled
to
the
output
valve
V8
which
provides
outputs
for
headphones
at
jacks
3KA
and
JKB
and
outputs for
a
600
ohm
line
and
for
a
3
ohm
loud
speaker
at
the
secondaries
of
the
output
transformer
ml.
4.6
AUTOMATIC GAIN
CONTROL
CIRCUITS
The
input
to
the
automatic
gain
control
diode V7b
is
taken
from
the primary
of
the
last
intermediate
frequency
transformer
IPr6
via
the
capacitor
C64. The
full
AGC
voltage
is
applied
to
the
second
mixer
valve
and
first
IF
anplifier and
approximately
one
sixth
of
the
AGC
voltage is
applies
to
the
two
signal-frequency
amplifiers.
A
choice of
two
AGC
time
constants
is
available
by
using
a
selector
board
inside
the
6974
receiver.
This
facility
is
required
for
high-speed
recording
applications.
7

The
automatic
gain
control
may
be
switched
in
or
out
by
the
operational
switch
on
the
front
panel.
This switch
has
seven
positions
which
include
the
following:
(a)
Standby
(b)
Third
oscillator
ON
(with and
without
AGC)
(c) Third
oscillator
OF?
(with
and
without
AGC
and
noise
limiter)
(d)
Crystal
calibrator.
4fl
NOISE
LIMITER
The
double-diode
elements
of
V9
operate
in
an
impulse
noise-limiting
circuit.
The
“series”
diode at
Pin
6
is
in
series
with
the
two
resistors
R50
and
R47
and
is
connected
across
the
resistor
R48
which
is
part
of
the
detector
load.
This
diode
is
normally
conducting
in
the
presence
of
a
signal
since
its
anode
is at
a
positive
potential
relative
to
the
cathode.
When
in
this
condition,
the
audio-frequency
potential
developed
at
the
cathode
is
passed
to
the
control
grid
of
the
first
AF
amplifier,
the
triode
section
of
V7.
The
junction
of
1150
and
1147
is
held
at earth
potential
to
AF
signals
by
the
capacitor
C72
and
the
time
constants
of
the
circuit
are
such
that
a
noise
impulse
of short
duration,
equivalent
to
more
than
100% mod
ulation
of
the
signal
being
received,
will
cause
the
anode potentiel
of
V9
(pin
6)
to
drop
instantaneously
to
a
value lower
than
that
of
its
cathode
and,
therefore,
the
diode will
cease
to conduct.
Additional
protection
is
afforded
by
the
action
of
the
“shunt”
diode
V9
(pin
5)
which
by-passes
to
earth
through
C72
any
excessive
noise
impulse
which
may
appear
at
the
anode
before
the
“series”
diode
has
ceased
to
conduct.
4.8
CRYSTAL
CALIBRATOR
I
The
triode
elements
of
V9
may
be
switched
to
work
as
a
crystal-controlled
oscillator,
the frequency
being
controlled
by
an
AT
-
cut
crystal
of
low
temperature
—
coefficient.
The
oscillator
circuits
are
dimensioned
to
provide
strong
harmonics
of
the
fundamental
500
kc/s oscillations
and
its
output
is
coupled
via
the
capacitor
C83
to
the
second
tuned
circuit
of
the
receiver.
The
amplitude
of
these
harmonics
is
sufficient
for
checking
the
receiver
calibration
at
any
multiple
of
500
kc/s
up
to
32
Mc/s.
4.9
DESENSITISING CIRCUIT
I
The
cathode
bias
to
the
KS
and
IF’
stages
can
be
increased
by
introducing
a
variable
resistor
RVQS
between
earth
and
the
gain
control
potentiometers.
Terminals
marked
DESF24SITISING
on
the
terminal
board
enable
this resistor
to
be
connected
to
the
keying
relay
or
to
back
contacts
on
the
transmitting
key.
The
receiver
may
thus
be
fully
or
partially
muted
during
transmission.
I
4.
10
SUPPLY
UNITS
For
operating
the
receiver
from
an
AC
source,
the
Supply
Units
Type
1325/4
and
Type
1325/5 are
provided.
The
two
types
are
identical
electrically,
each
employing
a
metal
rectifier
and
paper
dielectric
capacitors.
The
Type
1325/4
is
intended
for
table
T.2719/I
mounting
and
the
1325/5 for
rack
or
cabinet
mountings.
6974
8
L
I

The circuit
diagram
Fig.8
shows
that
the
mains
are connected
to a
two
pin
plug
from which
connections
are made
via the
ON/OFF
switch
and
2-amp
mains
fuses
to
the
transformer
primary.
Tappings
are
provided
for
any standard
supply
voltage
in
the
110
volt
or
220 volt
range.
An
HT
fuse,
rated
at
500mA,
is
connected
between
the
centre
tap
on the
AT secondary
and
earth.
The
280 volt
DC
and
6.3
volt Ac
outputs
are
connected
to
a
5-pin
socket
anunted
at
the
back
of the
chassis.
A
connector
cord
and
plug
convey
the
supplies
to
the receiver.
The
inputs
and
outputs
of the
Supply
Units
are as
follows:-
Input
200-250
volts,
50
to
60
c/s
single-phase
AC.
(Tappings
at
100, 215,
230
and
250
volts
permit
adjustments
to suit
available
mains voltages).
Outputs
280
volts
DC
at 65mA.
6.3
volts
AC at
4
amps.
consumption
60 watts.
5 INSTALLATION
5.1
FOR
MAINS
WORKING
The
Supply
Unit should
be
connected
to
the receiver
by
the connector cable
terminated
by
a
7
pin socket.
It is
important
to
check
that
the
primary
taps
on
the
mains
transformer
in
the Supply
Unit
are
set
to
suit the
supply
voltage
before
switch
ing on
the mains.
The
mains
should
be
connected
to
the Supply
Unit
by
means of
a
3-core cable
fitted
with
a 5-amp
plug.
5.2
FOR
RATTEIHES
OR FROM
OTHER
DC SOURCE
The
Supply
Unit
is not
required
when
the
receiver
is to
be
operated
from a
DC
source.
The
DC
supplies
should
be
brought
to the
7-pin
plug
on
the
receiver
as
follows:
-
Pins
1
and
7
to
LT 6.3
volts
Pins
2
and
3 to
LT earth
Pin
4
to
AT
positive
Pin 5
to
HT
earth
Protective
fuses
should
be connected
in
the supply
lines.
5.3
AERIAL
INPUT
CONNECTIONS
Two
coaxial
input
sockets are
located
at
the back
of
the
receiver
for
a balanced
—[
input
75
to
100
ohms.
For an
unbalanced
input
from a
single
coaxial
feeder,
one
r.2719f1
socket
only
is used
and the
inner
and outer
conductorsof
the
other
socket
are connected
6974
together.
With
the
same
arrangement
direct
connection
may
be made
to
an aerial.
9

I
5.4
OUTPUTS
Terminals
marked
LS
and
LINE
located
on
the
rear
of
the
receiver
chassis
are
provided
for
connection
to
a
3-ohm
loudspeaker
and
a
600
ohm
line
respectively.
Two
telephone
jacks
mounted
on
the
front
panel
are
for
use
with
either
high
or
low
resistance
headphones;
two
pairs
of
headphones
may
be
used
simultaneously
but
one
high
and
one
low
resistance
pair
connected
in
parallel
will
not
give
satisfactory
results.
5.5
DESENSITISING
FACILITIES
I
In
a combined
transmitting
and
receiving
installation
it
may
be
necessary
to
mute
the
receiver
during
transmissions.
For
this
purpose
two
terminals
marked
DESENSITISING
are
provided
at
the
back
of
the
receiver
and
are
normally
strapped
together.
When
nuting
is
employed
the
shorting link
should
be
removed
and
the
terminal
connected
by
a
screened
pair
of
leads
to
the
transmitter
keying
relay,
or
back
con
tacts
on
the
transmitting
key.
I
When
the
transmitter
key
is pressed
the
RF
and
IF
Cathode
bias
in
the
receiver
is
increased
by
introducing
all
or
part
of
an
additional
2500
ohm
variable resistor
RV95
at
the
earthy
end
of
the
RF
and
IF
gain
controls
RV94
and
RV93.
By
moving
the cover
marked
D on
the
front
panel the
potentiometer
RV95
mounted
above
the
HF
GAIN
control
may
be
adjusted
by
a
screwdriver
so
that
the
operator
hears
the
transmitter
at
a
convenient
level.
5.6
AGC
TERMINALS
AND
TIME
CONSTANT
ADJUSTMENT
For
normal
operation
the
AGC
terminals
1
and
2
at
the
rear
of
the
receiver
should
be
strapped
together.
The
AGC
time
constant
adjustment
consists
of
a
two-pin
connecting
link
and
a
small
insulated
panel
with
three
pin
sockets
mounted
immediately
to
the
right
of
V7
and
Vl3
on
the
top
deck
of
the
receiver chassis.
The
position
marked
0.5pF
gives
a
time
constant
of
approximately
0.2
secs.
for
the
MOD,
position
and
1.75
secs.
for
the
CW
position
of
the
operational
switch;
this
position should
be
used
for
normal
working.
The
position
marked
0. 1F
gives
a
time
constant
of
approximately
0.5
secs.
for
the
CW
and
the
MOD.
positions of
the
operational
switch;
this
position should
be
used
for
high-speed
recording
when
the
receiver
is
used
with
a
Type
Wi. 11
or
other
similar
type
of
Recording Unit.
I
5.7
DIVERSITY
CONNECTIONS
When
a
receiver forms
part
of
a
diversity
equipment
the plug marked
EXT.
08G.
at
the
back
of
the
receiver
chassis,
is
used
to
enable
two
or
more
receivers
to
be
supplied
from
an
external
common
first
oscillator;
when
thus
employed,
the
first
oscillator
selector
switch
(SWE)
on
the
front
panel
should
be
set
to
EXT.
OSC.
The
input
required
from
the
external
oscillator
is
approximately
I
volt
into
68
ohms).
An
output
at
465
Icc/s
is
provided
for
use
when
an
IF
operated
unit
is
employed
in
conjunction
with
the
receiver.
The
AUG
terminals
1 and
2
should
be
strapped together
and
connected to
the
AGC
T.27191
terminals
on
the
other
receiver.
6974
10
I

6
OPERATING
INSTRUCTIONS
6.1
GENERAL
Assuming
that
the
installation
has
been
carried
out
in
accordance
with
Section
5,
the
receiver
may
be switched
on and
set
up
for
reception
on
the
appropriate
signal
frequency.
The
sequence
of
operations
for
tuning the
receiver
and
the
use
of
the
various
controls
are as
follows:
6.1.1
PrelIminary
Adjustments
(a)
Switch
on AC
MAINS
and
switch
on Supply
Unit.
The
pilot
lamp
and
scale
illuminating
lanps
should
light.
(b)
Set
operational
switch
to
CW/MAN.
(c)
Set
passband
switch
to
3
kc/s.
(d)
Set
A?
GAIN
control
to
mid-position.
(e)
Set
HF
GAIN
control
to
maximum
(fully
clockwise),
reducing
if
necessary
to
give
comfortable
level
in headphones.
(f)
Set
SAND-CHANGE
switch
to
frequency
band
required.
The
frequency
calibration
for
each
hand
is
automatically brought
into
view
on the
calibration
drum
as
the
BAND-CHANGE
switch
is operated.
(g)
Set
the
pointer
on
the calibration
scale
to
the
desired
frequency
by
turn
ing
the
larger
tuning
knob,
and
locate
the
wanted
signal
by
using
the
small
knob.
If
telephony
is
to
be
received,
set
the
operation
switch
to
MOD/MAN.
and
re-tune
slightly.
Reduce
the
signal
to
a
suitable
level
by
turning
the
1W
gain
control
counter-clockwise.
(h)
During
short
stand-by
periods
the
HT
supply to
certain
valves
may
be
cut
off
by
turning
the
operational
switch
to
the
OFF
position.
6.1.2
Use
of
PASS
BAND
Switch
The
13
kc/s
passband
gives
best
intelligibility
for
reception
of
speech
and
also
makes
the
tuning
broader,
but
this
passband
may
be
used
only
when
little
interference
is
present.
As
the
passband
is
narrowed
by
switching
from
8
kc/s
to
3 kc/s
and
then
to
1 kc/s,
interference
will
be
cut
down
progressively
but
the
signal
must
be
tuned
in
more
carefully
and
accurately.
NOTE:-
lThen
receiving
CW
with
the
passband switch
at
13
lw/s
or
8 lw/s,
it
will
be
found
that
on
tuning
through
zero
beat,
the
beat
note
obtained is equally
strong
on
both
sides
of
zero,
but
when
using
the
3
lw/s
or
I
lw/s passband
the
beat
note
will
be
stronger
on
one
side
than
the other.
Always
tune
to
the
stronger
of
the
two.
6.1.3
Use
of
AGC
.2719/1
AGC
should
be
switched
off
(operational
switch
to
MAN.
position)
when
searching
6974
or when
strong
interference
is
present.
11

I
6.1.4
Use of
Gain
Controls
(a)
With AGC on, set
HF GAIN to
maximum and AF
GAIN as desired.
(b)
With AGC off, set
HF GAIN
as desired and AF
GAIN to
approximately mid-
I
position
I
6.1.5
Use of
calibrator
When the
operational
switch is set
to the CALIBRATE position,
a
500
kc/s oscil
lator is
switched
on
and a calibrating
signal
may
be
heard every 500
kc/s
up to 32
Mc/s.
6.1.6
Use of Meter
as Tuning
Indicator
When
the FEEDS
switch
(S4D) is set to the
SIGNAL INDICAThR
position
the meter
may
be
used
as
a tuning
indicator. Before using
the meter in this
way,
it
must be set to
give zero
reading in
the absence
of a signal as follows:
(a)
Set the
operational switch
to MOD-AGC
and the
HF
GAIN
control nearly to
maximum.
I
(b)
Adjust
the tuning control
to a silent
point.
(c)
Adjust the
SIGNAL INDICATOR
ZERO control,
which is mounted
on the chassis
I
deck
until zero reading
is obtained.
With the meter
switch set
to the other positions
the
valve feeds of Vi to
V6
and yb
to
V13 may be measured;
with the HF GAIN
control at
maximum these
feeds should
be within the
limits specified
in Table 8.
I
6.1.7
Use of Noise
Limiter
The noise
limiter is operative
for
all
receiving positions
of the
operational
F’
switch except
position 2
(MOD. AGC,
NL.
OFF).
h
The noise limiter
does, however,
introduce some
unavoidable
distortion of
mod
ulation
peaks, and so when
receiving transmissions
of high
quality, music or
speech,
it
should be
switched off by setting
the
operational switch
to
position
2.
I
6.1.8 Use
of Logging Scale
This scale enables
the operator to
reset the
receiver accurately
to a station
that has been received
previously.
Some slight
allowance
for
initial
frequency drift
should be made
if
the receiver has
been switched on for
less
than
30
minutes.
Read the scale
divisions from
right to left,
main divisions
on
the
upper scale
I
and sub-divisions on
the lower scale.
Note that the scale
reading
increases as the
frequency
is
increased.
The
approximate
discrimination
of the scale
at the lowest, middle
and highest
T.2719/
frequency in
each band is given in
Table 4.
6974
12
[
I