C MARKETING INSTALLATION
Issue 1, Apr 82
KEY AND LAMP UNITS No's 2A AND 10A
The Key and Lamp Units Nos. 2A and 10A are both designed to meet two primary applications,
order table working and speech broadcasting, which can be made
locally. With wiring modifications they may also be used to provide Key and Lamp Units for a limited range of
non-standard applications. This Instruction describes the units and associated apparatus
for use in the two primary applications.
Key and Lamp Unit No. 2A
The keys and lamps are in the same plane to allow the key-panel to be console-mounted if
required. The unit has ten lamps, ten 1000-type keys and a non-locking microswitch. It is
wired for ten basic line circuits but additional springs on the tenth key are wired to the
connection strip to enable it to be used for purposes other than as a line key if
necessary. The wiring-form from the keys to the connection strip includes three spare
wires for use in modifications. In the units as issued the keys are wired for speech
broadcast applications and this permits coupling between lines which is not normally
permitted for exchange line or PBX extension line terminations. The modification to the
key wiring to prevent the customer connecting lines together is shown on Diagram SA9157
The unit is two-tone grey with an acrylonitrile-butadiene-styrene copolymer (ABS)
cover, which can be removed by loosening two screws at the rear. The key panel is
supported by two pivoted brackets, giving easy access to the wiring and components.
Key and Lamp Unit No. 10A
The flange on which the micro- switch is mounted makes the unit unsuitable for console
mounting. This unit has two sets each of ten lamps and ten 1000-type keys and a single
micro switch. Each set of ten lamps and ten keys is wired identically to the Key and Lamp
Unit No. 2A, there being two sets of connection strips to which the two sets of lamps and
keys are independently wired.
This item is also two-tone grey. The ABS cover can be removed by loosening two screws at
the rear. The key-panel is supported by two pivot brackets giving easy access to the
wiring and components.
Jack Unit No. 1B
The operator's circuit associated with the key and lamp unit is housed in this unit, which
is normally fitted to the underside of a desk. The unit includes the speech-circuit
elements of a 700-type telephone on a printed wiring board, a Jack No. 84A and a
French-grey ABS cover. A Headset No. 1 or a Handset No. 3 is
plugged in to complete the circuit. Jack Unit No. 1B supersedes Jack Unit No. 1A.
Regulator No. 6B
To eliminate transmitter noise when short exchange or PBX extension lines are connected to
the installation it may be necessary to use a Regulator 6B in conjunction with Headsets Nos. 1 & 2. The Regulator No. 6B has been designed to be
associated with a Jack Unit No. 1B. Should a Regulator No. 6B be required with a Jack Unit No.
1A it must be fitted using a Block Terminal 36.
Unit, Auxiliary Apparatus, SA 9151
This unit accommodates five, line terminations for exchange lines or PBX extensions. It
also includes a flashing circuit consisting of a group of relays providing ten outlets of
interrupted earth-pulses to flash the calling lamps. There is space for addition of a
second distribution relay if more than ten outlets are required. A mains-fail relay for a
6V a.c. supply can also be fitted for use if required.
The equipment is accommodated on a 19 in x 5.25 in mounting-plate suitable for rack
mounting. A cover is included.
Unit, Auxiliary Apparatus, SA 9152
This unit accommodates five line circuits identical with those in the Unit, Auxiliary
Apparatus, SA 9151 but has no flashing circuit. The mounting-plate is 19 in x 3.5 in and
it is suitable for rack mounting. A cover is included.
Unit, Auxiliary Apparatus, SA 9153
This unit accommodates the line terminations for five private circuits on a 19 in x 3.5 in
mounting-plate suitable for rack mounting. A cover is included.
The normal signalling arrangements are:-
- Generator/earth-loop in, generator/a.c. out or,
- Generator/d.c. bothway. The unit is primarily intended for speech-broadcast working.
- In cases of complaints of poor transmission on any circuit terminated on a UAA SA 9153
modify the UAA in accordance with Works Specification S(W) 2090.
- Unit, Auxiliary Apparatus, SA 9219 This unit provides lamp flashing equipment only,
there is provision for five additional 3000 type relays, i.e. Mains-fail, Night Alarm or
additional flashing relays. There is provision for mounting a bridge rectifier in addition
to the relays for use with the Mains-Fail relay.
STRIP MOUNTED SET 1A1/SA 9207
This unit comprises two control relay-sets for the combined use of PO headsets on
customers approved radio circuits and PO lines with access for recording speech. The
mounting plate dimensions are 19 in x 5 in and it is suitable for rack mounting. A cover
ORDER TABLE WORKING
In certain organisations much of the incoming telephone traffic is often of a type
requiring information be be quickly supplied in response to inquiries. A system where a
group of operators is specially detailed to deal with such traffic is known as order table
working; railway inquiry bureaux as an example. The essence of such an installation is
speed in answering and to this end a group of lines, usually exchange lines or PBX
extensions, is multiplied over a number of key and lamp units. An incoming call on one
line is indicated by a lamp signal for that line at each unit and is answered by the first
free operator. Operating the answering key causes the appropriate lamp to glow at all
positions as a visual-engaged signal (VES). Similarly, when any line is taken into use to
originate a call a VES is given to all operators. A holding facility is provided on each
line to enable an operator to hold one line while speaking on another, the VES will
continue during hold conditions. Intercommunications between lines is prohibited by
rearranging the wiring to each answering key when the equipment is first installed.
Order table working with Key and Lamp Units Nos. 2A and 10A.
Method of Use
A single lamp per line on each Key and Lamp Unit is used to provide both calling and
visual-engaged signals. An incoming call causes the lamps to flash on every unit to which
it is connected. There is an audible alarm which is common to all circuits, a switch is
provided so that the audible alarm can be cut off when required. An alarm on a single
circuit maybe provided in accordance with Diagram SA 9157 Sheet 9. The visual engaged
condition is indicated by a steady glow. When not in use all keys are in the up (Receive
Call) Position. To answer a call a free operator moves the appropriate key to the down
(Speak) position, the appropriate lamp glowing at each of the multiplied units indicates
to all other operators that the call has been accepted. Should the answering operator wish
to hold the call the key is moved to the mid (Hold) position. At the end of the call the
key is restored to the up position and the multipled lamps darken. If the lines are PBX
extensions a microswitch operated by the press button can be wired to provide recall and
In standard order table installations the first five lines are terminated on a Unit,
Auxiliary Apparatus, SA 9151, which also provides the lamp-flashing equipment. Additional
lines are terminated on Units, Auxiliary Apparatus, SA 9152 (one unit for every five extra
circuits). For up to ten lines each operator has on Key and Lamp Unit No. 2A, a jack unit
with headset or handset and usually a drawer-mounted dial; other dial-mountings are
permissible to meet local requirements, or a telephone can be used as the operating
instrument if the subscriber prefers. For 11-20 line installations each operator requires
a Key and Lamp Unit No. 10A. Installations of more than 20 lines can be arranged but must
be specially assessed by the GM.
The 50 V dc supply is provided by a Power Unit No. 52A and its output is sufficient for an
installations of up to 20 lines, i.e., an installation containing one Unit Auxiliary
Apparatus, SA 9151 and up to three Units Auxiliary Apparatus, SA 9152. The 6v ac supply is
provided by either a Transformer No.261A for 3 up to 150 lamp appearances or a Transformer
No. 315A which will cater for up to 400 lamp appearances.
The Transformer No. 261A should be mounted inside the Power Unit No. 52A by using two
straps made locally. Later issues of the power unit will have holes drilled in positions
suitable for securing the transformer direct to the base plate. The primary (Mains)
winding of the transformer should be connected in parallel with the primary winding of the
power unit mains transformer so that the mains fuse protects both transformers. The 6v
a.c. output circuit should be protected by using a fuse No. 36A/7 fitted in either the FS3
or FS4 position (depending on permanent wiring) and removing the strap between FS3 and FS4
(see Dgm N 637). The transformer No. 315A is unshrouded and is too large for mounting
inside the power unit. A protective cover having adequate ventilation should be
constructed locally to guard the transformer from accidental contact. The cover should
also enclose the associated fuses and terminal blocks and be effectively earthed. The
primary (Mains) circuit of the transformer should include a Fuse No. 36A/2 and a Block
Terminal No. 21/3 for connecting the mains lead. A Fuse No. 57A/... of adequate rating for
the installation and a Block Terminal No. 21/2 for connecting the 6v a.c. output
conductors should be included in the secondary circuit.
In speech broadcasting systems a spoken message is transmitted by a controlling operator
over a number of lines simultaneously. The lines are frequently private circuits, but
exchange lines may also be so connected. Under broadcast conditions an out-station can
signal back to the operator, who has to suspend the broadcast and move the appropriate
line key from the 'Broadcast' to the 'Speak Single' position to deal with the caller
individually. With the extension of STD, exchange line broadcasting tends to diminish
because of timed local calls but may still be retained as an emergency facility or to give
service to subscribers awaiting the installation of private circuits. Where a single
operator broadcasts to a large number of lines a broadcast amplifier is necessary to
compensate for the teeing losses in the office. It does not raise the level of speech
transmitted to line nor does it compensate for line loss. The principle users of speech
broadcasting systems are subscribers whose primary requirement is the rapid dissemination
of up to the minute information.
Speech broadcasting using Key and Lamp Units Nos. 2A and 10A.
Method of use
When used as a speech broadcast switchboard a single Key and Lamp Unit No. 2A can only
accommodate nine lines, the tenth key being used as the 'Operator Broadcast' key. If
several units are coupled together under the control of one operator, however, only one of
the units is restricted to nine lines. Similarly a Key and Lamp Unit No. 10A will
accommodate nineteen lines, the last being used as the 'Operator Broadcast' key. 'When not
in use all the keys are in the mid-position (Receive Call). To answer a single call the
appropriate line key is moved to the up position (Speak Single). However a private circuit
broadcast is usually originated by the operator. The line keys of the circuits to be
included in the broadcast are moved from the normal mid-position to the up position (Speak
Single) and the common ring key (microswitch) pressed to apply ringing. When all stations
are ready to receive the broadcast the line keys are moved to the down position (Speak
Broadcast) and the 'Operator Broadcast' key is moved down to complete the broadcast
Should an outstation wish to call the operator during the broadcast, the call button is
pressed causing the lamp on his particular line to glow. To deal with the call the
operator must restore the 'Operator Broadcast' key and move the line key of the calling
circuit to the 'Speak Single' position. On exchange line broadcasts the outstation usually
originates the call, which causes the line lamp to glow. The operator answers in,the
'Speak Single' position and connects the line to the broadcast by moving the key to the
'Speak Broadcast' position. The recall facility is not provided on exchange lines. To hold
condition is either from the Operator's circuit or from the broadcast matching
transformer; there is no 'Hold' position for the keys.
Various speech broadcasting arrangements using K & LU's 2A are provided for
Exchange Telegraph Co. These are listed in TI EL C4195.
Private circuits are terminated on Units, Auxiliary Apparatus, SA 9153 and exchange lines
on Units, Auxiliary Apparatus, SA 9152, each unit taking five circuits. The number of key
and lamp units will depend on local requirements. The operator's circuit is equipped with
a jack unit, a headset or handset, and on exchange lines, a suitably mounted Dial.
Miscellaneous equipment for the operator's circuit includes a matching transformer
appropriate to the type of line and battery-feeding arrangements or one more Units
Amplifying No. 23D.
The 24v d.c. supply is derived from a mains operated Power-Unit No. 57A, but where a
suitable supply already exists this may be used. A separate 6v a.c. supply is not required
as the lamps are fed, each in series with a resistor contained within the key and lamp
unit, from the 24V d.c. supply. Current consumption is small since, under broadcast
conditions, only the operator's instrument is energised, the rest of the equipment being
Apart from the two main uses described the key and lamp units are designed so that with
the minimum of modification they can be adapted to provide non-standard requirements for
which a key and lamp unit is necessary. If extensive modification is required
consideration should be given to the use of Case No. 174A Key and Lamp Unit No. 12A (A Key
and Lamp Unit No. 2A minus keys and wiring) or Mountings D 92135 and D 92199 as
alternatives. Dgm SA 9157 has been introduced to satisfy a number of requests to terminate
private circuits on order table installations. The modifications necessary to effect
exchange prohibition are shown, and also the various locally constructed relay-sets
required for different methods of signalling when this cannot be achieved with Unit
Auxiliary Apparatus SA 9153. A circuit to give inter-communication between operators on
two separate groups of order tables has been included and the facility to provide a
separate audible alarm for one circuit in a group or for a single circuit on one key and
lamp unit in a group is also shown.
CONSOLE-MOUNTING OF KEY-PANELS
To meet demands for console mounted key- panels the Key and Lamp Unit No. 2A, Incomplete,
is available. (See Drg 91613). It comprises a key-panel with its wiring-form and
connection strips. The method of fitting should be devised locally, depending on the
console provided by the subscriber. The key-panel of Key and Lamp Unit No. 10A is not
suitable for console mounting.
Where the subscriber requires the installation to function during interruption of the
mains supply, the request should be dealt with locally and be the subject of special
assessment by the GM. It is pointed out that on order table installations a separate
battery supply will be necessary to provide power for the lamps, which need a far larger
current than the rest of the equipment. Since a suitable 6V rectifier is not provided by
the PO it is suggested that a Rectifier No. 105A be used and the lamps changed to Lamps
No. 2 12V-20. For larger installations a rectifier with a greater output should be
METHOD OF CHANGING LAMPS
Key and Lamp Unit No. 2A Remove the lamp cover by sliding the retaining clips at each end
towards the centre and lifting the cover. The lamp jack strip which is then exposed may be
drawn forward by unscrewing the fixing screws at each end enabling a lamp to be gripped
for removal and replacement.
Key and Lamp Unit No. 10A Remove the individual plastic lamp cover by pulling it away
from the key-panel to expose the lamp. Remove the lamp with an Extractor No. 5.
The following diagrams are available:-
SA/SAW 9151 - Unit, Auxiliary Apparatus SA 9151. Five exchange line terminations and
lamp flashing equipment
SA/SAW 9152 - Unit, Auxiliary Apparatus, SA 9152. Five exchange line terminations
SA/SAW 9153 - Unit, Auxiliary Apparatus, SA 9153. Five private circuit terminations
SA/SAW 9154 - Key and Lamp Units Nos. 2A and 10A
SA/SAW 9155 - Jack-unit No. 1A
SA 9156 - Order table working using Key and Lamp Units No. 2A and 10A. Up to 20 exchange
lines or PBX extensions
SA 9157 - Order table working using Key and Lamp Units No. 2A and 10A. Special
SA 9160 - Speech broadcast working using Key and Lamp Unit No. 2A. Up to nine exchange
lines or PBX extensions
SA 9161 - Speech broadcast working using Key and Lamp Unit No. 2A. Up to nine private
SA 9162 - Speech broadcast working using Key and Lamp Unit No. 2A. Up to nine private
circuits with amplifier
SA 9163 - Speech broadcast working using Key and Lamp Units No. 2A and 10A. Over nine
exchange lines or private circuits
SA/SAW 9207 - Strip mounted set 1A1/SA 9207. Control relay set for order table equipment
having common use of PO headset on PO lines and subscribers radio equipment.
C MARKETING INSTALLATION
KEY AND LAMP UNITS NO. 2B AND 10B
The Key and Lamp Units Nos. 2B and 10B are connectorised versions of the Key and Lamp
Units No. 2A and 10A respectively. All existing features of the Key and Lamp Units No. 2A
and 10A are retained. Key and Lamp Units Nos. 2B and 10B include Connectors No. 226
mounted within the rear of the units to effect a speedier installation.
Connectors No. 226 are terminated using "Insulation Displacement Termination
The unit is two-tone grey with Acrylonitrile-Butadiene-Styrene copolymers (ABS) cover,
which can be removed by loosening two screws at the rear. The key panel is supported by
two pivoted brackets giving easy access to the wiring and components. The connector No.
226 is mounted by two special screws (4/DSC/575) on a "H" shaped bracket. This
bracket is secured to the base by four screws. The unit has ten 1000 type keys, ten lamps
and a non-locking microswitch all which are mounted in the front plate of the unit. It is
wired for ten basic line circuits and the tenth key has additional springs which are wired
to the connection strip to enable it to be used for purposes other than a line key if
necessary. The wiring-form from the keys to the connection strips mounted on the base
contains three spare wires which can be used for modifications. The wiring-form from the
226 connector is terminated to the connection strips by either wire-wrapping or soldering.
This cable form also includes four spare wires which can be used for additional circuits.
The units are issued with the keys wired for speech broadcast applications and this
permits coupling between lines, which is not normally permitted for exchange line or PBX
extension line terminations.
The modification to the key wiring to prevent the customer connecting lines together is
shown on Diagram SA 9157 Sheet 1.
This is only part of the TI.
Introduced in 1964.
Click here the the circuit diagrams (PDF)