Alba 7701 User manual
SERVICE
ALBA
MANUAL
AM/FM
SUPERHET
STEREOGRAMS.
Models
7701
-
7802-7903
ALBA
7701
GENERAL
SPECIFICATION
Models
7701-7802-7903
employ
the
same
chassis,
but
differ
in
respect
of
the
types
of
cabinet
and
loudspeaker
used.
They
are
designed
for
normal
or
stereophonic
record
reproduction,
in
addition
to
the
reception
of
A.M.
broadcasts
in
the
Long
and
Medium
waves
and
of
frequency-modulated
signals
in
the
range
87-100
mc/s
(Band
II).
Waveband
and
Radio/Gram
selection
is
by
means
of
interlocked
push-button
switching.
The
output
from
the
two
identical
audio
sections
is
used
in
parallel
for
radio
reception
and
when
playing
‘monaural’
recordings.
Ganged
Tone
Controls
are
used;
and
the
knobs
of
the
two
independently
adjustable
Volume
Controls
are
friction-fitted,
so
that
after
balance
between
the
two
channels
has
been
achieved,
the
adjustment
of
one
knob
controls
the
volume
from
both.
Audio
output
is
approximately
4
watts
per
channel.
Valves:
VI
(ECC85)F.M.
R.F.
amplifier
and
mixer.
V2
(ECH81)—A.M.
mixer/osc.;
F.M.
1st
I.F.
amplifier.
V3
(EBF89)—A.M./F.M.
2nd
I.F.
amp.;
A.M.
detector
&
A.V.C.
V4
(EB91)—F.M.
Ratio
Detector
double-diode.
V5
(ECC83)—1st
audio
amplifier
(one
half
per
channel).
V6
)
^
|
(EL84)—audio
output
(one
per
channel).
V8
(EZ81)—H.T.
rectifier.
CIRCUIT
DESCRIPTION
F.M.
R.F.
&
Osc.:
Signals
from
the
F.M.
aerial
socket
are
coupled
by
the
aerial
transformer
to
the
cathode
of
the
first
triode
of
the
ECC85
(VI),
which
acts
as
R.F.
Amplifier,
permeability
tuned
by
LI,
with
C3
as
R.F.
trimmer.
The
R.F.
output
from
this
valve
is
coupled
via
a
bridge
circuit
to
the
second
triode
of
the
ECC85,
which
acts
as
a
mixer/oscillator
with
a
permeability
tuned
osc.
transformer
L2
and
Cll
as
trimmer.
A.M.
R.F.
&
Osc.:
Signals
from
the
M.W.
or
L.W.
aerial
windings
on
the
ferrox-rod
are
fed
to
the
grid
of
the
mixer
section
of
the
ECH81
(V2)
via
the
band-change
switch,
the
secondary
winding
of
the
F.M.
Tuner
I.F.T.
(Tl),
and
C18
(100
pf).
R.F.
tuning
is
by
means
of
C17
section
of
the
gang,
with
tracking
trimmer
Cl6.
The
fixed
tuning
condenser
C15
is
in
circuit
on
L.W.
only.
The
triode
portion
of
the
ECH81
functions
as
oscillator.
Osc.
coils
L6
and
L5
are
selected
by
the
band-change
switch
for
M.W.
and
L.W.
respectively.
Oscillator
tuning
is
by
means
of
C28
section
of
the
gang
with
trimmer
C27.
I.F.
&
Detection:
The
I.F.
is
470
kc/s.
L9/10
and
L14/15
are
the
A.M.
I.F.
trans¬
formers,
shunted
by
the
200
pf
capacitors
C22,
C23,
C35,
C37.
The
effect
of
the
F.M.
I.F.
transformers
in
series
with
them
is
negligible
at
470
kc/s,
and
they
in
turn
have
negligible
effect
at
the
F.M.
I.F.
of
10.7
mc/s.
Detection
is
carried
out
by
one
diode
of
the
EBF89
(V3),
the
other
being
strapped
to
cathode.
A
portion
of
the
detected
signal
is
applied
as
A.V.C.
to
V3
and
the
mixer
section
of
V2,
via
R16,
decoupled
by
C30,
and
R6.
The
H.T.
feed
to
the
F.M.
Tuner
valve
VI
is
disconnected
when
the
receiver
is
set
to
A.M.
I.F.
&
Detection:
The
modulated
I.F,
appearing
at
the
mixer
anode
is
coupled
to
the
heptode
section
of
the
ECH81,
which
now
acts
as
1st
I.F.
amplifier,
by
the
I.F.
output
transformer
Tl
on
the
Tuner.
H.T.
feed
to
the
anode
of
the
A.M.
oscillator
is
disconnected.
L7/8
and
LI
1/12/13
are
the
2nd
F.M.
and
Ratio
Detector
transformers.
A
separate
double-diode
(V4,
EB91)
is
used
for
detection.
Detected
A.F.
voltages
appear
across
C.38.
R14
and
C39
form
the
de-emphasis
network.
continued
over
CIRCUIT
DESCRIPTION
(
c
ontd
.
)
AUDIO
For
radio
reception,
the
3rd
section
of
the
band-switch
selects
signals
from
either
the
A.M.
or
F.M.
detectors.
These
signals
are
fed
via
C48
(.lfxF)
to
the
4th
(Radio/Gram)
section
of
the
switch,
which
selects
radio
or
gram
inputs
to
the
audio
amplifier
systems.
The
cartridge
fitted
to
the
record-player
unit
is
designed
to
be
compatible
for
monaural
and
stereo
recordings.
For
monaural
playing
the
cartridge
elements
feed
an
identical
signal
into
points
‘W’
and
‘X’,
which
are
connected
via
the
switch
to
the
right
and
left-hand
reproduction
channels
respectively.
On
stereo
each
cartridge
element
is
separately
activated
via
the
single
stylus
by
signals
recorded
on
either
side
of
the
record
groove.
The
two
channels
are
identical.
An
input
selected
at
the
Radio/
Gram
switch
is
taken
to
one
of
the
Volume
Controls,
from
whose
slider
it
is
fed
via
a
.OlpiF
condenser
to
the
grid
of
one
section
of
the
ECC83
double-triode.
Amplified
signals
appearing
at
the
anode
of
this
valve
are
fed
to
the
grid
of
the
EL84
output
pentode.
The
‘earthy’
side
of
the
Volume
Control
is
connected
to
a
Tone
Control
network
which
depends
on
frequency
selective
feedback
from
the
secondary
of
the
O.P.T.
Output
impedance
is
3
ohms
nominal.
The
tape
recorder
socket
is
connected
between
“test
point
TP2”
and
chassis.
TOP
VIEW
OF
PANEL
Please
note:
C42
is
shown
incorrectly
connected.
The
negative
side
should
go
to
RI8/C4I
MAIN
CHASSIS
A.M.
ALIGNMENT
First
check
for
output
on
both
audio
channels.
Then
proceed
as
follows:—
Output
meter
to
be
connected
across
one
O.P.T.
secondary
and
the
dummy
load
across
the
other.
Both
Volume
Controls
to
be
set
to
max.
and
Tone
Controls
fully
clockwise.
Input
from
the
generator
must
be
kept
as
low
as
possible
to
prevent
operation
of
the
A.V.C.
Important:
Where
two
tuning
peaks
are
founds
the
‘outer’
is
the
correct
one.
I.F.
Alignment:
(1)
Signal
Generator
set
to
470
kc/s,
30%
modulated
at
400
cps.
Switch
the
receiver
to
M.W.
with
the
gang
fully
meshed.
Inject
the
signal
from
the
generator
at
gl
of
V2
(between
tag
2
on
the
Tuner
Unit
and
chassis)
with
the
oscillator
section
of
the
gang
shorted
out,
and
adjust
the
slugs
of
L9,
L10,
L14
and
LI5
for
maximum
output.
Repeat.
Calibration
and
R.F.:
(2)
Check
that
the
scale
pointer
lines
up
with
the
‘start’
dot
on
the
scale
pan
when
the
gang
is
fully
meshed.
The
shorter
leg
of
the
pointer
is
used
for
calibration.
(3)
Inject
600
kc/s
modulated
signal
across
the
A.M.
coupling
winding
‘A’
on
the
Ferrox-rod,
with
the
pointer
set
to
the
500m
dot,
and
adjust
the
slug
of
the
Medium
wave
osc.
coil
L6,
and
the
aerial
coil
L4
(on
the
Ferrox-rod)
for
max.
Note:
On
both
M.W.
and
L.W.
it
is
important
to
re-check
the
tuning
of
the
appropriate
osc.
coil
each
time
the
aerial
coil
is
adjusted.
(4)
With
the
pointer
set
to
200m,
inject
1500
kc/s
and
adjust
trimmers
C16
and
C27
on
the
gang
for
max.
(5)
Re-check
calibration
at
500m
and
200m
and
adjust
if
necessary.
(6)
Switch
the
receiver
to
L.W.
and
inject
200
kc/s
signal
as
at
(3),
with
the
pointer
set
to
the
appropriate
dot
on
the
scale
pan.
Adjust
the
L.W.
osc.
coil
L5
and
aerial
coil
L3
(on
the
Ferrox-rod)
for
max.
Repeat.
(7)
Disconnect
the
generator
and
check
calibration
with
the
receiver
tuned
to
the
Light
Programme
at
1500m
(200
kc/s).
F.M.
ALIGNMENT
I.F.:
Switch
the
receiver
to
F.M.
and
inject
an
unmodulated
signal
at
10.7
mc/s
as
at
(1),
with
a
50fxA
meter
in
series
with
a
100K
resistor
or
equivalent
uni¬
versal
meter
connected
between
Test
Point
1
and
chassis
(meter
nearest
to
chassis).
(8)
A
djust
the
slugs
of
L7,
L8
and
Lll
for
maximum
reading
on
the
I
meter.
Note
the
reading
at
this
point.
i
(9)
Connect
the
meter
and
resistor
as
above,
between
Test
Point
2
and
!
chassis,
and
adjust
the
slug
of
L12
to
give
a
reading
which
is
half
1
that
obtained
at
Test
Point
1.
Repeat
operations
(8)
and
(9).
If
it
should
become
necessary
to
re-align
the
Tuner
Unit,
the
following
procedure
should
be
adopted:—
LF.:
(10)
Inject
an
unmodulated
10.7
mc/s
signal
via
a
suitable.01
^F
condenser
between
tag
4
on
the
Tuner
Unit
and
chassis.
Adjust
the
slugs
of
T1
(Tuner
I.F.
output
transformer)
for
maximum
reading
on
the
50
fiA
meter
at
Test
Point
1.
Calibration:
(11)
With
the
gang
condenser
fully
open,
the
grub
screw
on
the
Tuner
spindle
must
rest
against
the
front
(horizontal)
stop.
Disconnect
the
generator
and
connect
an
F.M.
aerial.
With
the
receiver
tuned
to
93.5
mc/s,
the
pointer
should
be
opposite
the
appropriate
calibration
dot,
(±^
r
/
is
permissible).
Adjust
trimmers
C3
and
Cll
if
necessary.
DISMANTLING
INSTRUCTIONS.
7701
Remove
the
front
four
knobs,
i.e.
two
volume,
on/off,
tone
and
tuning.
Remove
the
back
covers
of
the
radio
compartment,
changer
and
(from
the
back)
right-hand
loudspeaker
compartments.
Withdraw
the
plugs
from
the
rear
socket
panel,
aerial,
L.S.,
etc:
also
the
plug
from
the
power
pack
in
the
right-hand
compartment,
withdraw
the
record
player
shelf.
The
chassis
can
now
be
removed
by
unscrewing
the
holding
down
bolts
from
underneath
this
compart¬
ment,
the
retaining
screws
for
the
socket
panel
can
also
be
removed.
The
power
pack
is
held
by
screws
which
are
withdrawn
from
underside
of
cabinet.
7802
Remove
the
front
four
knobs,
i.e.
two
volume,
on/off,
tone
and
tuning.
Remove
the
back
covers
of
the
Radio,
changer
and
right-hand
com¬
partment
(from
the
rear).
The
plugs
from
the
rear
socket
panel
and
power
pack
should
be
removed,
the
socket
panel
is
removed
from
the
back
rail
of
the
chassis
compartment
by
withdrawing
the
two
retaining
screws.
The
chassis
retaining
screws
are
located
in
the
top
of
the
changer
compartment.
SCALE
PAN
\
TURN
TURNS
7903
Remove
the
cabinet
back
from
the
Radio
compartment,
remove
the
panel
carrying
the
AE,
loudspeaker,
P.U.
etc:
held
by
two
screws.
Detach
the
octal
plug
from
the
power
pack.
To
remove
the
chassis
open
the
set
as
for
normal
tuning,
pull
off
the
four
control
knobs,
then
remove
the
two
retaining
clamps,
one
at
each
end
of
scale
(each
being
held
by
two
wood
screws).
Remove
the
scale,
lifting
it
out
of
its
bottom
groove
(replace
in
reverse
way
by
placing
the
top
end
in
first,
and
sliding
bottom
edge
into
groove).
The
chassis
base
board
which
slides
into
retaining
slots
is
held
by
two
bolts
which
are
reached
from
the
rear,
base
board
is
withdrawn
from
the
front.
To
remove
Changer
Unit,
pull
out
the
P/U
plug
and
remove
mains
connection
to
the
motor,
this
being
accomplished
by
removal
of
the
bottom
panel,
and
the
changer
compartment
panel
on
the
back.
The
15
watt
230-240v
lamp
is
fitted
into
the
right-hand
loud¬
speaker
compartment,
giving
light
to
the
record
section,
access
from
rear
by
removal
of
the
appropriate
panel.
Care
must
be
exercised
to
ensure
that
all
leads
are
refitted
in
the
same
place
from
which
they
are
removed,
this
will
prevent
hum
being
introduced.
ALL
MODELS
The
changer
unit
is
held
by
transit
bolts
which
have
turn
over
clips,
these
clips
should
be
turned
parallel
to
the
transit
bolts
for
withdrawal
purposes.
Care
should
be
taken
to
ensure
that
wiring
is
replaced
in
the
original
locations.
DRIVE
CORD
ASSEMBLY
with
the
gang
fully
closed
CONTINUITY
SPARES
Item
Part
No.
Mains
T.X.
T6
12328
O.P.T.’s
T4/5
11411
Vol.
Controls
Concentric
500K+500
K
Log
12333
Tone
Controls
Ganged
10K+10K
Log
with
switch
12332
T2
Combined
AM/FM
I.F.T.
12330
T3
AM/I.F.T.
+FM
Ratio
Det.
Trans.
12331
Ferrox-rod
Assy.
12359
FM
Tuner
Unit
12341
Scale
7903.
13252
7802.
13251
7701.
13250
No.
Component
Ohms
approx.
T1
F.M.
Tuner
I.F.T.
L3
1
L4
J
A.M.
Aerial
Windings
j
4
1
L5
L6
[
A.M.
Osc.
Coils
|
9
4
L9/10
1st
A.M.
I.F.T.
each
winding:
10.5
L14/15
2nd
A.M.
I.F.T.
each
winding:
10.5
L?
i
2nd
F.M.
I.F.T.
j
0.5
L8
j
0.75
Lll
1
|
0.4
L12
Ratio
Detector
Transformer
|
0.25
L13
)
|
v.
low
T4/5
Sound
O.P.T.’s
primaries:
375
secondaries:
0.25
T6
Mains
Transformer
primary:
0-200v
11
0-215v
12.25
0-235v
13.5
secondaries:
H.T.
75+75
heaters
v.
low
ALBA
(RADIO
&
TELEVISION)
LTD.,
TABERNACLE
ST.,
LONDON,
E.C.2.
G6384
Numbers
in
squares
\
3^|
are
on
F.M.
unit.
Letters
in
rectangles
jXj
are
for
panel
and
associated
block
connections.
Letters
in
circles
(J)
are
pane!
fly
lead
connections^
as
shown
on
panel
illustration.
,\
—
\
\--
Pick-up
5
on
extern*
SWITCHES
SHOWN
WITH
LW.
BUTTON
DEPRESSED
tration.
GANGED
TONE
CONTROLS
CSO^
1-25
VOLUME"”
1
1
CONTROL
1
R29
<-5K
R30
iOK
+
d.p.
switch
F-M.
Unit
VOLUME
GANGED
TONE
CONTROLS
This manual suits for next models
2
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