Early Exchanges
...connecting the UK
Early Exchanges
Very early exchanges used a variety of signalling systems produced by different manufacturers as the most suitable form of switchboard and exchange design evolved over the years. The Central Battery (CB) exchange was the preferred method of providing service in large towns.


Image: Telecom Technology Postcard - Boy operators working the Sunderland exchange in 1883.
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Early Exchanges

Staffing overview

Early exchanges employed young boys to answer and connect the calls. However, young ladies had a better demeanour for this type of work and thus manual, and later auto-manual, exchanges were staffed predominantly by female employees. Night staff doing 'through nights' were mostly male and this division of the sexes continued until (approx.) the early 1980s when there was less discrimination in the workplace.


Exchange Types

As the Telephone Service expanded, the simpler types of signalling were superseded by more complex solutions which could serve a greater number of subscribers. In the days before automatic switching, these were the common types of manual exchanges:


  • Slipper Jack
  • Magneto
  • Central Battery (CB)
  • Central Battery Signalling (CBS)
  • Central Battery Signalling with Subscriber's multiple (CBSm)

Here's  a summary of the key features of each type:-

Slipper Jack Exchange

Single wire, earth return. Local battery in subscribers' premises.
Drop indicators to show calling line.
Patching jacks to connect calls.
Two operators needed.
Trembler bells for calling.
No automatic 'clear-down'.


Magneto Exchange

Single wire, earth return.
Local battery in subscribers' premises.
Magneto indicators to show calling line.
Multipled jack appearances.
Magneto bells and hand generators for calling.
Magneto signal to 'ring-off' or 'clear-down'.


Central Battery (CB)

Exchange Pair of wires used.
Central battery in exchange.
Use of signalling relays and
Supervisory lamps to show calling line.
Multipled jack appearances.
Separation of cord circuits from  speaking & ringing keys.
Magneto bells for calling.
'Clear-down' signal given when handset replaced.



Central Battery Signalling (CBS) Exchange  

For exchanges without a mains supply.
Central battery in exchange for signalling.
Local battery retained at subscribers' premises for transmitter current.
Drop indicators used to show calling line.
Magneto bells for calling.
'Clear-down' signals:

CBS1 - earth on 'A-line.
CBS2 - disconnection.


CBSm Exchange

A CBS exchange equipped with a subscribers' multiple suited to larger exchanges.



Central Battery Types

The majority of switchboards favoured the Central Battery design, the four main types being:
 
  • C.B. No.1   with a capacity for up to 10,000 subscribers' lines.
  • C.B. No.10  for up to 2800 subs' lines, but could be extended to 4200, if required.
  • C.B. No.12  as type 10, but with series (break jack) multiple.
  • C.B. No.9    an 800 line multiple exchange which used indicators. 
 
Enfield Manual Board CB1
Enfield Manual Board CB1
The Central Battery (CB) exchange was the preferred method of providing service in large towns.



Photo: Enfield CB1 when it was on display in the Dugdale Centre © Light Straw Archive July 2012.
   

 
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