Alba 7701 Manuale utente

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

CONTROL

1

R29

<-5K

R30

iOK

+

d.p.

switch

F-M.

Unit

VOLUME

GANGED

TONE

CONTROLS

Alba 7701 Manuale utente

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