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Technical Pamphlet for Workmen - CBS CBS is short for Central Battery Signalling which superseded the Magneto system. The central battery being used for signalling only. Diagram C.B.S. 3 is dated 1905. CBS systems, of which there were three types, were designed by the Post Office and from 1923 CBS No's 2 and 3 systems were standard for all exchanges that were not large enough to justify the provision of Central Battery equipment or where a Rural Automatic Exchange would not meet the requirements. The CBS systems provide automatic signalling similar to that of the Central Battery system. The difference being that the telephones used on a CBS system had a local battery (two cells) to power the microphone and the central CBS exchange had a battery that supplied power for signalling purposes. Central Battery systems also used the battery in the exchange for both signalling and transmission. CBS No. 1 is a "loop call" and "earth clear" system in which the signals are automatically controlled by the removal and replacement of the telephone receiver. The CBS No. 1 was superseded by the CBS No. 2 and 3. There were many reasons for this, but in practice the CBS No. 1 was found lacking due to unreliable earth provision at the customers premises and the 250ohm bell ringer being part of the signalling system, which reduced the subscribers line to a loop resistance of only 500ohms. The CBS No. 1 floor pattern also used a combined lamp and relay unit on the subscribers line circuit, which was difficult to access for maintenance. The CBS No. 3 operation was similar to CBS No. 2 but the system capacities were greatly reduced and consisted of small wall pattern switchboards with an ultimate capacity 2 or 5 junctions and 20 subscriber circuits. Smaller CBS switchboards could be found in rural areas, residing in Post offices and the occasional private house. The system is contained within a wooden switchboard or Multiple sections and the range extends from a small four line wall pattern model to a large floor pattern multiple exchange with a maximum capacity for 800 lines. The switchboards are connected to a main trunk switchboard by means of Junctions and these circuits terminate on jacks with an associated calling indicator. The subscribers line circuits also terminate on jacks and have an associated calling indicator which can be either "eyeball" or "drum" types. The CBS No. 2 switchboards use a "disc" type indicator. Connection of Junctions and Subscriber lines is by means of cords and these have associated supervisory indicators, generally of the "eyeball" type. The cords are in pairs and are plug ended. Larger switchboards use lamp signalling, which allows jacks to fitted per panel. Ringing is by hand generator. A CBS No. 1 multiple switchboard suite is made up of two panel switchboard sections with the subscriber line and outgoing junction multiples every four panels. Both the CBS No. 1 and No. 2 can be connected to Automatic exchanges. When junctions to Automatic exchanges are provided a dial is fitted and on the CBS No. 1 special dialling jacks are associated with each outgoing junction. On the CBS No. 2 it is possible to dial through the calling plug and a special dial key is provided for this purpose. The CBS No. 3 had no provision for Automatic working.
Article on the CBS Standardisation to CBS No's 2 and 3 The system was designed to work in rural areas, where in some places there was no mains power supply. The power requirements at the switchboard were reduced to a bare minimum by installing transmitter batteries at the customers instrument. Where there was no mains supply the batteries were primary cells and required considerable maintenance, but if mains was available, a power unit would be installed and the maintenance overhead reduced. Generally the main batteries were installed in two banks, working main battery and reserve battery, which were connected to the switchboard via a changeover switch. No reserve batteries were installed on the smallest 10 line switchboard. Each battery set consists of 20 cells in series (24 volts), but where current consumption was large two or more 20 cell battery sets could be joined in parallel on the working main battery. The battery change over switch was used to switch over the batteries if they went flat or required maintenance. The change over switch can be seen in many of the pictures below either on the front or on the right of the switchboards. There were also three other 2 cell sets of batteries and these powered, the operators transmission circuit, the operators reserve transmission circuit and the alarm bell circuit.
Telephones generally used on CBS systems are:- Party Lines On a 2 subscriber party line an X station telephone is joined up in the same way as that of an exclusive line subscriber - that is, with the bell connected between the "A" line and earth, but at a Y station the bell is connected to the "B" line and a condenser is inserted between the bell and earth. On 12 subscriber party lines the bells at all the X stations are connected to the "A" line and those at all the Y stations to the "B" line. At all the Y stations and at all the X stations except the last one, however, a condenser is inserted between the bell and earth at each station. At the last X station, which should be the station most distant electrically from the exchange, the condenser in the bell circuit is omitted in order that a clearing signal may be given to the exchange in the ordinary way at the close of a call from any of the stations. The exchange rings 2 subscriber party line subscribers selectively and 12 subscriber party line subscribers semi-selectively, by code rings. An X station is called by ringing over the "A" line of the circuit and a Y station by ringing over the "B" line. The normal connections of the exchange ringing device are such that when a cord circuit calling plug is inserted in a subscriber's jack and a ringing key is depressed, bells connected to the "A" line will be actuated. X stations are, therefore, rung in the same way as exclusive line subscribers, but to enable stations with bells connected to the "B" line to be called, a reversal of the ringing connections is necessary. To provide for this a ringing reversing key is fitted on each operator's position in non-multiple exchanges and in many multiple exchanges, but in modern exchanges of the latter type this special key is dispensed with by allotting two jacks per multiple in the subscriber's multiple to each party line circuit. On one of these jacks the tip and ring connections are reversed. X stations can, therefore, be rung on one jack and Y stations on the other in the ordinary way. On 2 subscriber party lines each subscriber hears only the rings intended
for his own station. On 12 subscriber party lines each X station receives a
ring for any X station, and similarly each Y station bell is rung whenever
the call is for a Y station. Each station should, however, take notice of
and reply only to its own distinctive number of rings. PBX Working CB PBX Switchboards could also be connected the CBS exchange by the use of an
Unit, Auxiliary Apparatus No. 18. Central Battery Signalling No. 1 Instruments
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Type of Exchange | 1930 | 1936 |
Central Battery Signalling, Multiple | B10 | CBSm |
CBS No. 1 - Lamp Signalling, Non-Multiple | BL1 | CBS1 |
CBS No. 1 - Indicator Type, Non-Multiple | BX1 | CBSL1 |
CBS No. 2 - Non-Multiple | BL2 | CBS2 |
CBS No. 3 | BX3 | CBS3 |
Switchboard Types
CBS No. 1 Switchboards (Most common types)
Designation | Type | Dimensions | Subscribers | Junctions | Cord Circuits | Features | |||||
Width ft ins |
Depth ft ins |
Height ft ins |
Equipped | Capacity | Equipped | Capacity | Equipped | Capacity | |||
2+4 (10) CBS207 | Wall | 0 11 | 0 8 | 1 9 | 4 | 8 | 2 | 2 | 2 | 2 | Eyeball inds |
5+20 (45) | Wall | 1 8 | 1 1 | 2 2 | 20 | 40 | 5 | 5 | 5 | 5 | Drum inds |
5+10 (45) | Floor | 1 8 | 2 2 | 5 1 | 10 | 40 | 5 | 5 | 10 | 10 | Eyeball inds |
5+20 (45) CBS333 | Wall | 1 8 | 1 3 | 2 2 | 20 | 60 | 10 | 10 | 7 | 10 | Drum inds |
5+60 (135) | Floor | 1 8 | 2 2 | 5 1 | 60 | 120 | 5 | 15 | 14 | 14 | Drum inds |
20+60 (140) | Floor | 1 8 | 2 2 | 5 1 | 60 | 120 | 20 | 20 | 14 | 14 | Lamp inds |
CBS 1 Multiple | Floor | 1 11 | 3 5 | 6 5 | 60 | 200 | 30 | 70 | 17 | 17 | Lamp inds |
CBS No. 2 Switchboards (Most common types)
Designation | Type | Dimensions | Subscribers | Junctions | Cord Circuits | Features | |||||
Width ft ins |
Depth ft ins |
Height ft ins |
Equipped | Capacity | Equipped | Capacity | Equipped | Capacity | |||
5+20 (50) CBS473 | Floor | 1 9 | 2 3 | 4 7 | 20 | 40 | 5 | 10 | 7 | 10 | Disc inds |
5+20 (70) CBS473 | Floor | 1 9 | 2 3 | 4 7 | 20 | 60 | 10 | 10 | 7 | 10 | Disc inds |
20+60 (160) CBS481 | Floor | 2 2 | 2 3 | 4 11 | 60 | 100 | 20 | 60 | 12 | 14 | Disc inds |
30+60 (160) CBS481 | Floor | 2 2 | 2 3 | 4 11 | 60 | 100 | 30 | 60 | 12 | 14 | Disc inds |
20+60 (240) | Floor | 2 1 | 2 10 | 6 4 | 60 | 180 | 20 | 30 | 14 | 16 | Disc inds |
CBS No. 3 Switchboards
Designation | Type | Dimensions | Subscribers | Junctions | Cord Circuits | Features | |||||
Width ft ins |
Depth ft ins |
Height ft ins |
Equipped | Capacity | Equipped | Capacity | Equipped | Capacity | |||
2+5 (22) CBS488 | Wall | 1 4 | 1 3 | 2 8 | 5 | 20 | 2 | 2 | 3 | 5 | |
2+20 (22) | Wall | 1 4 | 1 3 | 2 8 | 20 | 20 | 2 | 2 | 3 | 5 | |
5+20 (25) | Wall | 1 4 | 1 3 | 2 8 | 20 | 20 | 5 | 5 | 3 | 5 |
Switchboard Pictures
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CBS No. 1 - 2+4 (10) Picture dated 1921 |
CBS No. 1 - 5+20 (45) 1921 |
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CBS No. 1 - 5+10 (45) Picture dated 1926 |
CBS No. 1 - 20+60 (140) Picture dated 1921 |
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CBS No. 2 - 5+20 (50) Picture dated 1924 Click here for more information |
CBS No. 2 - 30+60 (160) Picture dated 1928 |
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CBS No. 2 - 5+20 (50) Internal view with the front swung open Picture dated 1924 |
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CBS No. 2 - 30+60 (240) Picture dated 1926 |
CBS No. 3 - 2+5 (22) Picture dated 1926 |
CBS No. 1 at Grantham
Picture dated 1947
CBS No. 1
Five position multiple suite using lamp signalling
CBS No. 2 at Four Elms, Tonbridge, Kent
The switchboard is a 20+60 (160)
Picture taken 1935
CBS No. 2 at Littlewick Green
Picture taken 1947
Glenmoriston CBS No. 3 Exchange
The Post Office at Invermoriston circa 1880.
The road is the main highway to Skye.
The Post Office circa 1980's after the maim road had been realigned
The picture shows an extension to the left of the building which was for the
Post Office
CBS No. 3 5+ 20 (25)
Note the alarm bell, battery changeover and docket holder switch on the
right hand side of the case
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