Ericsson Dialog Parts list manual

·.

DIALOG

Technical Description

6/DLG

TCI Library www.telephonecollectors.info

CONTENTS

1.

Introduction

3

2.

General

4

3.

Desi

gn 6

3.1

Base

plate

7

3.2 Ring

er

8

3.3

Transmission

unit

10

3.4

Dial

unit

12

3.5

Instrument

case

13

3.6

Cords

15

3.7

Handset

16

3.8 Wall

terminal

box

19

4.

Description

of

the

transmission

regulation

device

21

5.

Transmission

properties

24

6.

Dismantling

and

reassembly

during

maintenance

26

7.

Maintenan

ce

31

TCI Library www.telephonecollectors.info

1.

INTRODUCTION

Ever

since

its

foundation

in

1876 L M

Ericsson

has

designed

and

produced

telephone

instruments

of

different

versions.

One

link

in

the

chain

of

standard

telephone

instruments

is

Dialog

which

incor-

porates

the

latest

research

techniques

, new

construction

materials

and

the

results

of

our

wide

experien

ce

as

designers

and

manufac-

turers

.

Dial

og

is

attractive

in

appearance

and

has

ex

ce

llent

tech-

nical

qualities.

Furthermore,

the

technical

and

desi

gn

aspects

have

been

matched

to

the

maintenance

requirements

.

This

description

refers

to

the

desk

version

of

Dialog

but

is

also

valid

for

the

wall

version

as

the

me

c

hanical

design

and

technical

f

ea

tures

follow

the

same

principles.

The

transmission

properti

es

described

are

g

iven

for

Dialog

with

automatic

transmission

regu-

lation.

3

TCI Library www.telephonecollectors.info

4

2.

GENERAL

Dialog,

equipped

with

dial,

is

intended

for

connection

to

automatic

main

exchanges,

private

automatic

exchanges

and

private

automatic

branch

exchanges

(fig. 1).

Fig.

1

Dialog

In

designing

this

instrument,

the

aim

has

been

to

make

telephoning,

i.e.,

the

dialling

and

handling

of

the

instrument.

as

comfortable

as

possible.

and

to

enable

the

instrument

to

be

easily

carr

ied

(fig. 2).

With

this

aim

in

mind,

the

most

attractive

design

has

been

created

as

a

result

of

close

cooperation

between

engineers

and

industrial

designers.

This

means

among

other

things

that

the

instrument

constitutes

a

single.

compact

design,

attractive

from

all

angles

(fig.

3a-3c),

Fig.

2

Dialog

is easy

to

carry

'I

·

1·

TCI Library www.telephonecollectors.info

Fig.

3 a

Dialog

front

view

The

design

of

the

instrument

case

and

handset

,

the

mechanical

build-up.

as

well

as

the

circuit.

are

completely

new.

Tw

o

fa

cto

rs

have

contributed

to

these

alterations.

First.

the

utilization

of

new

materials

and

high-quality

electrical

components

available,

and.

secondly.

the

application

of

c

e.

Fi

g . 3 b

Dial

og

sid

e

vi

ew

Fi

g. 3 c

Di

al

og

re

ar

vi

ew

-

5

TCI Library www.telephonecollectors.info

6

3.

DESIGN

As

shown

in

fig. 4,

Dialog

has

seven

main

parts,

namely

Handset

with

cord

Instrument

cord

with

wall-terminal

box

Instrument

case

Base

plate

Dial

unit

Transmission

unit

Ringer

unit

Fig.

4

The

main

parts

of

Dialog

As

the

ringer

unit,

transmission

unit

and

dial

unit

are

keyed

into

the

base

plate

no

screws

are

required.

The

instrument

and

handset

cord

conductors

are

mechanically

connected

to

screw

terminals

on

the

transmission

unit.

The

instrument

case

is

fixed

to

the

internal

parts

by

means

of only

one

screw,

well

located

for

the

repairman

and

concealed

from

the

subscriber

(fig. 5).

Each

unit

has

its

own

function

and

can

be

replaced

by

an

identical

unit,

regardless

of

the

other

units.

The

assembly

method

enables

a

complete

telephone

instrument

to

be

built

up

of a few

units

,

each

of

which

comprises

several

components.

From

the

maintenance

point

of

view

this

is

a

most

valuable

method

of

design,

since

TCI Library www.telephonecollectors.info

Fig.

5

Onl

'Y one

screw

Ca

se

3.1

Base

pl

ate

Fig.

6

The

scr

ew

is

well

located

for

the

repairman

maintenance

in

the

field

can

be

carried

out

by

semi-skilled

staff,

with

a

minimum

of

tools

and

instruments.

Only a

screwdriver

is

required

to

replace

any

unit

(fig. 6). When

necessary,

repla

c

ed

units

can

be

repaired

at

a

central

workshop

where

qualified

staff,

tools,

and

instruments

are

available.

The

DIALOG-case

and

handset

are

moulded

in

acrylate

butadiene

styrene

(ABS),

and

are

manufactured

in

eight

colours.

The

dyes

or

pigments

used

for

colouring

have

been

chosen

c

arefully

to

ensure

colour-fastness.

The

plastic

material

offers

an

o

ptimum

of

hi

gh

impact-

and

scratch

resistance

and

can

easil

y

withstand

the

effects

of

falling

from

one

meter

on

to

a

hardwood

floor

.

The

handset

cradle

is

designed

so

that

line

disconnection

is

ensured

even

when

the

handset

is

lightly

or

carelessly

replaced.

Under

the

cradle

and

at

a

convenient

distance

from

the

handset

,

there

is

a

carrying

grip

to

facilitate

the

moving

of

the

telephone

instrument.

This

execution

is

far

superior

to

su

ch t

ype

s wher e

extra

arrangements

have

been

added

to

the

ca-se

afterwards

or

where

metal

handles

have

been

fixed

to

the

case

by

means

of

screws.

The

frame

for

the

subs

c

riber

number

is

fixed

to

the

front

of

the

case,

allowing

both

subscriber

number

and

routing

number

, or

nam

e of

exchange,

to

be

typed.

The

base

plate,

shown

in

fig. 7

is

made

of

sheet

steel,

zinc-electro-

plated

with

yellow

c

hromate

coating

and

laquered

. Unlike

L M

Ericsson~

s e

arlier

telephone

instruments,

the

base

plate

of

this

instrument

has

raised

edges

to

ensure

hi

gh

mechanical

stability.

The

various

units

can

then

be

keyed

into

the

base

plate

without

affecting

its

mechanical

strength,

despite

the

fact

that

thin

metal

is

used.

The

base

plate

has

four

non-slip

feet

of

neopren,

a

durable,

migration-free

synthetic

rubber,

which

hold

the

instru-

ment

steady

during

dialling

.

The

slots

in

the

base

plate

permit

re

g

ulation

of

the

ringer

and

supply

locking

support

for

the

various

units

to

be

mounted.

At

7

TCI Library www.telephonecollectors.info

3.2

Ringer

8

the

cord

inlet

in

the

base

plate,

a

hole

has

been

made

in

the

raised

edge.

The

cords,

which

can

thereby

be

rem

oved

one

at

a

time,

lock

each

other

and

ensure

a

tight

packing.

Fig.

7

The

base

plate

from

above

The

ringer

mechanism

(fig. 8

and

9)

is

mounted

on a

plate

(1)

provided

with

three

tabs

which

are

inserted

in

slots

in

the

base

plate.

In

addition

there

is

a

hole

in

the

centre

cf

the

ringer

mechanism

plate

in

which

a

projecting

stud

on

the

base

plate

fits

when

the

ringer

mechanism

has

been

correctly

l

oca

ted.

Fig.

8

The

bell

unit

The

ringer

is

connected

to

the

screw

terminals

of

the

trans-

·

mission

unit

by

means

of two

PVC

insulat

ed

conductors

.

eq

uipp

ed

with

cable

lugs.

The

ringer

is

of

the

polariz

ed

type

with

a

single

winding

(3)

and

a

small

AlNiCo

permanent

magnet

(2).

Th

e

flux

generated

by

the

permanent

magnet

and

the

flux.

or

iginatin

g

from

the

ringing

current.

is

superimposed

only

in

the

''air

gap'

',

which

gives

maximum

signalling

efficiency.

The

"air

gap"

is

easy

to

adjust

and

the

coil

is

replaceable.

The

coil

former

is

made

of

Formaldehyde-plastic

and

wound

with

copper

wire.

insulated

by

shellac.

All

the

iron

parts

are

zinc-electroplated

with

yellow

cro

mate

coating

and

laquered.

TCI Library www.telephonecollectors.info

Fig,

9

The

bell

unit

in

parts

The

gongs

(4)

are

of

sheet

brass

and

the

fixing

holes

are

eccentric

to

permit

easy

adjustment

for

maximum

sound

intensity

. Two

pillars

are

riveted

to

the

ringer-plate

in

order

to

support

the

gongs

and

the

resonator

cups

(5).

The

ringer

produces

a

pleasant

sound

,

penetrating

even

to

people

with

impaired

hearing

(limitation

of

hearing

generally

starts

at

high

frequencies).

These

important

properties

are

obtained

as

a

result

of

the

gongs

having

different

pitches,

and

the

subharmoni

cs

of

the

signal

being

amplified

by

Helmholtz

resonators

(5).

The

Ringer

Output

Spectrum

is

shown

in

fig. 10.

The

ringer

can

be

equipped

with

sound

regulation

if

required.

By

reducing

the

movement

of

the

bar

by

means

of a

tag

under

the

in-

strument.

the

sound

intensity

of

the

ringer

can

easily

be

altered

-

continuous

regulation

from

full

output (74 dBa)

to

the

soft

signal

of

a

buzzer

(45 dBa).

The

impedance

at

25

Hz

(c/

s).

with a 1 µ F

capacitor

in

series

with

the

bell,

is

4 500 Ohm.

and

at

800 Hz (c/

s)

36

000 Ohm.

9

TCI Library www.telephonecollectors.info

3.3

Transmission

unit

10

-5 2

70

dB

rel.

2 · 10

N/m

hll

511

40

0

JO

IS 20 kHz

Fig.

10

Rin

ger

output

sp

ectru

m

The

printed

board

is

made

of

insulating

material.

On

the

rear

side

there

is

a

printed

wiring

,

which

connects

all

the

component

s

in

the

transmission

unit.

The

components

are

gro

uped

on

the

other

side

,

bell

and

dial

and

cords

being

connected

to

the

board

with

screw

terminals.

The

transmission

unit

(fig.

11

)

comprises

induction

co

il

,

resistors,

capacitors

and

varistors

as

well

as

crad

le

-swit

ch

springset.

Details

of

these

components

are

given

in

the

following.

Fig.

11

The

trans-

mission

un

it

3,3.1

Ind

uction

coi

l

The

induction

coil

(fig. 12)

is

of

the

antisidetone

type

with

five

windings

and

a

C-core

of

laminated

silicon

iron,

protected

against

rust

by

means

of

varnish.

This

design

has

resulted

in

hi

gh

permeabilit

y

and

an

imp

ortant

saving

of

material.

High

inductance

values

have

been

ob

tain

ed

wit

h

moderate

copper

loss

es,

and

the

very

good

coup

lin

g

between

the

winding

sections

results

in

a

high

sid

eto

ne

attenuation.

(1

!l

TCI Library www.telephonecollectors.info

Fig.

12

Induction

coil

3.3.2

Resistors

The

resistors

(fig. 13

A)

used

in

Dialog

are

of

the

modern

carbon-

film

type

with

colour

code

or

value

marking.

They

are

fully

tropic-proofed.

3,3,3 Capacitors

Self-healing

metallized

paper

or

polyester

capacitors

(fig. 13B)

are

used

in

Dialog.

They

are

protected

against

moisture

by

being

moulded

in

epoxy

resin.

Each

single

component

comprises

one

capacitor.

_____

_,,__-----

Fig.

13

11

TCI Library www.telephonecollectors.info

3.4

Dial

unit

12

3.3.4

Varistors

Dialog

has

a

number

of

varistors

(13 C), one

working

as

shock

absorber

for

the

receiver

and

the

others

as

part

of

the

equalizing

network.

The

varistors

are

voltage

dependent

,

non-linear

resistors.

With one

exception

they

are

made

of

silicon.

The

exception

is

the

shock

absorber

which

is

made

of

selenium

and

moulded

in

epoxy

resin.

The

silicon-type

varistors

are

enclosed

in

glass

capsules.

Each

single

component

comprises

one

varistor.

Fig. 14

The

cradle

switch

springs

et

fitted

to the

insulating

sheet

3.3.5

Cradle-switch

springset

The

cradle

-switch

spring

set

(fig. 14)

consists

of 8

springs

(1)

with twin

contacts.

Together

with

insulating

spacers,

the

springs

are

mounted

directly

on

the

springset

frame

(4)

and

operated

by

a

cradle-switch

(3)

with

two

levers.

When

the

handset

is

lifted

a

tension

spring

(5)

operates

the

cradle

to

a

fixed

position.

On

replacing

the

handset,

two

plungers

are

depressed,

which

actuate

the

levers

and

the

cradle-switch

turns

over

to

its

first

position,

allowing

a

return

spring

to

reset

the

con-

tact

springs

via

a

lifting

comb

(2).

The

cradle-switch

frame

as

well

as

the

levers

are

made

of

sheet

steel.

Nylon

bearings

(6)

reduce

the

amount

of

friction

to

a

minimum

and

increase

the

life-time.

The

weight

of

the

handset

and

the

load

on

the

tension

spring

are

so

adjusted

that

good

function

and

a wide

margin

of

safety

are

achieved.

The

hook-switch

frame

contains

a

threaded

hole

for

the

single

screw.

by

means

of

which

the

instrument

is

opened.

The

dial

(fig. 15),

is

mounted

on

brackets

(1)

equipped

with

four

tabs

(2),

which

fit

into

four

slots

in

the

base

plate.

To

obtain

good

locking

effect,

these

four

slots

are

displaced

slightly

in

pairs.

The

covering

plate

(3) of

the

dial

is

furnished

with

figures

outside

the

finger

wheel

(4).

This

has

been

possible

since

the

plate

is

larger

than

on

earlier

conventional

types

of

telephone

instruments.

The

finger

wheel

is

made

of

transparent

plastic.

TCI Library www.telephonecollectors.info

Fig. 15 a The dial

unit-rear

view

Fig. 16

3.5 Inst

rume

nt

case

Fig. 15 b The dial

unit-front

view

The

dial

mechanism

is

the

same

as

in

L M

Ericsson's

instruments

and

is

guaranteed

for

an

average

of

one

million

operations,

which,

for

six-digit

numbers,

corresponds

to

18

dialled

calls

per

day

for

25

years.

The

dial

speed

is

easy

to

adjust

by

means

of a

screw-driver.

The

rim

of

the

impulse

cams

is

domed

to

provide

a

perfect

sliding

surface

for

the

impulse

springs.

The

impulse

cams

are

thus

protected

against

damage

from

the

edges

of

the

springs.

The

impulse

wheel

is

made

of nylon. Owing

to

the

low

friction

of nylon,

no

lubrication

is

necessary.

The

thermoplastic

material

used

in

the

instrument

case

(fig. 17)

gives

a

smooth.

colour-fast

surface,

which

has

good

resistan

ce

to

impact

and

is

not

easily

scratched.

It

is

not

affected

by

perspiration

,

skin

creams,

and

lipstick.

The

material

has

good

ageing

properties.

Water

and

soap

will

remove

almost

any

stain.

The

instrument

cradle

is

designed

so

that

the

handset

,

even

if

carelessly

replaced.

always

falls

into

the

correct

rest

position.

Fig

,

17

The

instru-

me

nt

case

13

TCI Library www.telephonecollectors.info

Fig.

18

The

grip

at

the

rear

of

Dialog

14

Fig.

19

This

is

the

way to

carry

Dialog

In

this

way

the

switching

equipment

of

the

exchange

is

not

unnec-

essarily

occupied,

nor

the

instrument

put

out

of

order

,

by

the

cradle-switch

springset

not

returning

to

home

position.

Under

the

handset

at

the

rear

of

the

instrument,

there

is

a

grip

(fig.

18-19).

By

inserting

the

fingers

in

this

pocket

and

gripping

the

handset

with

the

thumb

at

the

same

time,

the

instrument

can

easily

be

carried.

The

screw

for

fastening

the

instrument

case

is

located

inside

this

grip.

Fig.

20

The

sub-

scriber

number

frame

' 1 s

. q 0

The

front

of

the

instrument

is

provided

with

a

frame

(fig. 20)

for

fastening

the

subscriber

number

card.

This

frame

is

held

in

position

by

means

of a

spring

inside

the

case,

allowing

the

sub-

scriber

number

card

to

be

easily

inserted

without

any

removing

of

the

ca

sing.

Fig.

21

The

trans-

parent

inset

TCI Library www.telephonecollectors.info

3,6

Cor

ds

F

ig

.

23

The m echa

n-

ical

unl

oa

ding

of the

cord

.

Th

e dete

nt

is

fixe

d to a hole

in the b

ase

plate

F

ig

.

22

Handset

and

instru-

m e

nt

co

rds

a

re

mad

e

of

PVC

At

the

rear

of

the

instrument

there

is

a

transparent

plastic

inset

(fig. 21).

The

light

so

admitted

into

the

instrument

discourages

the

entry

of

insects.

The

inset

also

acts

as

a

support

for

the

selfretaining

screw

and

retains

the

plungers

when

the

case

is

removed.

The

inset

at

the

rear

edge

of

the

case

is

kept

in

place

by

the

flat

spring.

The

case

is

on

the

inside

provided

with

several

ribs

,

which

correctly

locate

the

case

relative

to

the

base

plate.

On

the

left-hand

side

of

the

case

(seen

from

the

front)

are

small

inlets

for

the

handset

and

instrument

cords.

The

cords

(fig.

22)

consist

of

three

PVC

insulated

conductors,

which

are

covered

by

a PVC

sheathing.

This

execution

prevents

humidity

from

penetrating

which

could

cause

shortcircuiting

between

the

conductors.

I

All

conductors

are

of

standard

tinsel

threads,

each

composed

of

4 x 2

flexible

cadmium

copper

alloy

tapes,

lapped

around

a

polyester

centre.

This

design

gives

maximum

flexibility.

The

conductors

,

insulated

by

PVC of

various

colours,

are

laid

side

by

side

to

form

a

core.

which

is

covered

by

PVC.

The

nominal

diameter

of

each

uninsulated

conductor

is

0. 8

mm.

The

thickness

of

the

PVC

insulation

is

0.25

mm

.

Thus

the

diameter

of

each

insulated

conductor

is

1. 3

mm.

The

overall

diamet

er of

the

c

ord

is

4.4

mm.

The

electrical

resistance

of

each

conductor

does

not

exceed

1.0

ohm/

mat

a

temperature

of

2o

o

c.

The

length

of a

normally

extended

handset

cord

is

1. 3 m

and

the

instrument

c

ord

is

1.7 m long.

The

conductors

are

provided

with

cable

lugs

for

the

connec

tion

to

the

terminal

screws.

The

instrument

cord

has

a

separate

conductor

for

connection

of

an

extra

bell

to

the

wall

terminal

box.

A

continuous

study

of

the

maintenance

of

instruments

has

shown

that

the

length

of

life

of

the

cords

depends

to

a

high

deg

ree

on

whether

or

not

mechanical

strain

is

allowed

to

spread

to

the

cable

lugs

and

screw

terminals.

A

cord

provided

with a

good

mechanical

unloading

device

to

relieve

the

strain

on

the

cable

lugs

,

has

a

longer

life

than

a

cord

with a

weak

mechanical

unloading

devi

ce.

15

TCI Library www.telephonecollectors.info

3,7

Hands

et

Fig.

24

The

hand-

s

et

16

The

handset

cord

and

the

instrument

cord

each

have

a

mechanical

unloading

devi

ce (fig. 23),

designed

as

metal

detents.

each

fastened

to

a

hole

in

the

base

plate.

The

other

end

of

the

handset

resp.

instrument

cord

has

the

same

unloading

device

which

fits

into

a

slot

in

the

transmitter

cup

in

the

l

ower

part

of

the

handset

resp.

into

the

wall

terminal

box.

The

handset

(fig. 24)

is

made

of

the

same

plastic

material

as

the

instrument

case.

The

handset

is

well

balanced

for

easy

and

comfortab

le

handlin

g.

The

distance

and

angle

between

the

earpiece

and

mouthpiece

are

especially

designed

to

provide

the

correct

speaking

position

for

the

average

telephone

user.

The

mouthpiece

is

of

the

flat

type.

Owing

to

its

design

and

position

in

relation

to

the

mouth,

the

voice

of

the

speaker

is

caught

in

the

most

suitable

way,

regarding

efficiency

and

intelli-

gibility

as

well

as

comfort.

The

earpiece

is

shallow

,

i.e.

it

provides

resonance

space

for

good

acoustic

matching

to

the

ear

volume.

Fig.

25

The

dif-

ferent

parts

of

the hand-

set

(Front

view

of

the

trans-

mitter

cup)

The

transmitter

and

receiver

insets

are

designed

as

easily

changeable

capsules

(fig. 25)

thus

facilitating

comfortab

le and

speedy

maintenance.

Contact

sprin

gs

are

silver

plated

to

ensure

good

contact.

The

receiver

has

screw

connections.

The

connection

wires

which

are

laid

inside

the

hollow

handset

shaft

are

easily

removed.

The

transmitter

is

placed

in

a

removable

cup

(fig. 25-26)

in

the

lower

part

of

the

handset.

The

rear

of

the

cup

is

provided

with

terminals

for

connecting

the

handset-cord

conductors

as

well

as

a

slot

for

the

mechanical

unloading

device.

TCI Library www.telephonecollectors.info

•

\

Fig.

26

The

trans-

mitter

cup

with hand-

set

cord

and the two

conductors

to the

receiver

3.7.1

Transmitter

The

external

shape

of

the

transmitter

can

be

seen

in

fig.

27.

The

transmitter

design

is

such

that

the

transmitter

characteristics

are

practically

independent

of

the

speaking

position.

The

ratio

(1,3:1)

between

the

highest

and

lowest

transmitter

resistance

provides

good

evidence

of

this

when

the

transmitter.

with

constant

feeding

voltage.

is

made

to

assume

all

possible

positions.

The

entire

surface

of

the

electrodes

(

6),

(14)

is

in

permanent

contact

with

the

carbone

granules

(3).

Consequentl

y,

the

whole

electrical

current

will

be

conducted

through

the

quantit

y of

carbon

affected

by

speech

vibrations.

The

stability

is

further

improved

by

the

rough

walls

of

the

granule

chamber.

which

prevent

the

carbon

granules

from

packin

g

during

conversation.

The

electrode

surfaces

are

gold

plated

to

achieve

the

best

possible

contact

between

them

and

the

carb

on

g

ranules

.

Fig.

27

The

trans-

mitt

er

At

high

frequencies

the

transmitter

response

curve

shows

an

increased

degree

of

sensitivity.

This

is

achieved

by

the

small

mass

and

frequency

dependant

stiffness

of

the

diaphra

gm

system

(15).

This

stiffness

is

also

a

function

of

the

loading

on

the

acoustical

volume.

The

total

acoustical

volume

consists

of

two

chambers

separated

by

the

transmitter

inset

frame.

Thus

the

transmitter

cup

forms

the

second

chamber.

This

frame

(11)

has

three

holes

covered

with

fabric

discs

(12), (13)

which

at

low

frequencies

have

virtually

negligable

acoustical

impedance

so

that

the

conical

diaphragm

is

loaded

by

the

total

air

volume

in

the

two

chambers.

The

acoustical

stiffness

of

the

system

at

low

17

TCI Library www.telephonecollectors.info

frequencies

is

therefore

small

and

the

response

curve

has

a good

basic

level.

Over

the

highest

range

of

transmitter

frequencies,

the

holes

are

closed,

since

there

is

not

time

for

full

pressure

equalization

between

the

two

chambers.

The

diaphragm

then

works

against

a

smaller

volume.

As

a

result,

the

combined

stiffness

in

c

reases

with

the

frequency

and

the

mechanical

resonance

curve

of the

oscillating

system

is

displaced

towards

the

higher

frequencies.

Covering

the

holes

with

fabric

discs

attenuates

sharp

resonance

peaks

and

smoothes

out

the

response

curve.

Fig.

28

The

transmitter

in

cross

section

and

parts

18

A

small

hole

(20)

has

been

made

in

the

diaphragm

to

counteract

adverse

static

pressure

with

air

pressure

variations

and

to a

counteract

disturbances

from

low

frequency

room

noise.

To

protect

it

against

mechanical

damage,

the

transmitter

is

provided

with

a

perforated

lid

(18).

Ingress

of

humidity

is

prevented

by a

polyutheran

disc

(17)

fixed

inside

the

lid.

The

capsule

design

and

the

choice

of

materials

ensures

that

the

trans-

mitter

maintains

its

good

characteristics

under

tropical

condi-

tions

.

3.

7.2

Receiver

Fig. 29

The

receiver

The

external

shape

of

the

receiver

can

be

seen

in fig.

29.

In

theory

the

receiver's

magnetic

system

is

of

the

conventional

type

,

but

by a

careful

choice

of

material

and

accurate

optimal

magnetizing,

a

considerable

increase

in

output

level

has

been

achieved.

The

receiver

body

is

of

phenolic

plastic.

(1)

The

diaphragm

(8)

is

made

of a

special

ferro-cobalt

vanadium

alloy

which

exhibits

high

reversal

permeability

with

normal

p

I

'D

TCI Library www.telephonecollectors.info

3.8 Wall

terminal

box

operating

flux

density.

An

additional

diaphragm

(9) of

sheet

iron

is

included.

and

serves

as

a

magnetic

shunt,

providing

a

further

increase

in

the

transfer

factor.

A

thin

aluminium

ring

(10)

separates

the

magnetic

shunt

from

the

protective

cap

(11).

The

receiver

inset

is

sealed

by

a

chromium

plated

brass

cover

(13).

The

short

ALNICO

steel

magnet

(

3)

which

has

high

coercive

force

is.

together

with

its

pole

pieces

(4).

cast

into

the

receiver-well

by

means

of a

corrosion-proof

metal

(2)

which

expands

when

cooling.

This

method

provides

an

extremely

stable

mechanical

anchorage

and

ensures

at

the

same

time

that

the

correct

air

gap

is

maintained

between

the

pole

pieces

and

the

diaphragm.

Grinding

of

the

pole

pieces

is

unnecessary,

which

makes

it

possible

for

us

to

avoid

any

risk

of

altering

the

magnetic

properties.

The

thermoplastic

coil

bobbins

(5)

have

been

designed

to

form

a

wall

in

the

space

behind

the

diaphragm,

creating

two

acoustical

chambers.

The

response

curve

is

evened

outby

the

same

method

as

applied

in

the

transmitter,

i.e.

a

hole

(6)

covered

by

a

fabric

disc

(7).

This

design

is

most

effective

in

smoothing

the

response

curve

over

the

high

frequencies

and

thereby

ensuring

correct

reproduction

of

the

weaker

sounds.

Fig. 30 The

receiver

in

parts

and

cross

section

The

receiver

side

of

the

telephone

instrument

has

dry

contacts,

screw

terminals

(14),

as

only

a.c.

flows

through

the

contact

positions.

Fig.

31

The wall

terminal

box

1 2 3

19

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