PABX No. 6

TELECOMMUNICATIONS INSTRUCTION
C MARKETING - INSTALLATION
3 Internal
F 1660

Scope of Instruction
This Instruction describes the facilities and equipment of the PABX 6.

General
The PABX 6 is an unattended PABX, i.e. it is not attended by an operator, and incoming exchange calls are answered by certain designated extensions and transferred to the required extension.

It has capacity for 5 exchange lines, 20 extensions and 4 connecting circuits. Two inter-switchboard circuits may be provided in place of two exchange lines, if required.

The Equipment, PABX 6 consists of a cabinet 3ft 9in wide, 5ft 4in high and 1ft 2in deep, which contains the basic equipment and wiring necessary to enable relay-sets, Uniselector mechanisms etc, to be fitted to give the required number of exchange lines, extensions, connecting circuits and inter- switchboard circuits.

Facilities
The following general facilities are provided as standard. Further details are given in the relevant circuit Diagram Notes.

(a) Designated extensions
These are pre-determined extensions which are able to answer incoming exchange calls. Any extension may be so designated but the maximum number of designated extensions for which provision is normally made is eight. This number may be increased to twelve if necessary at the expense of night-service facilities. This reduces the number of possible night-service arrangements by the capacity of one night-service relay.

(b) Non-designated extensions
These are extensions which are unable to answer incoming exchange calls.

(c) Incoming exchange calls
An incoming exchange call rings common bells strategically placed in the building. When the handset of any designated extension is lifted the exchange call is automatically connected to it.

(d) Outgoing exchange calls
Access to an exchange line is obtained from an extension by pressing the telephone instrument button. For a short period during the setting-up of this connection a connecting circuit is employed, but if all the connecting circuits are busy, an alternative method of switching is used to ensure access to a free exchange line.

(e) Exchange call barring
Designated extensions may be barred outgoing exchange calls. Non-designated extensions may be barred incoming or outgoing exchange calls.

(f) Extension-to-extension calls
These are dialled direct using connecting circuits. The connecting circuit is held for the duration of the call. An extension may also dial another extension or a switchboard operator over an inter-switchboard circuit, dependent upon the type of P.B.X. at the distant end.

(g) Inquiry calls
While an extension is engaged on an incoming or outgoing exchange call, inquiry calls may be made to any other local extension, or, over an inter-switchboard circuit, to other PBX operators and extensions by pressing the instrument button and dialling the appropriate number. During the period of the inquiry the exchange line is held. On completion of the inquiry the original extension may return to the exchange call by re-pressing the instrument button.

(h) Transfer
An extension having made an inquiry call to a second extension while holding an exchange call may transfer the call to the second extension. This is done by asking the second extension to hold while the handset of the originating extension is replaced. Transfer does not take place if the inquiry has been made to an extension which is barred exchange calls, or to an extension or operator over an interswitchboard private circuit. If for any reason transfer does not take place, the original extension is recalled automatically.

(j) Ring when free
If a designated extension makes an inquiry call and finds the required extension engaged, the designated extension will normally return to the exchange line and inform the subscriber. If the subscriber decides to hold, the designated extension may re-dial the required extension number followed by the additional digit 1 and then replace the receiver Provided that the required extension is not barred incoming exchange line calls, the exchange call is their 'parked' on the required extension line which is automatically rung when it cleats from the previous call. The exchange call is connected through when the handset on the required extension is lifted.

(k) Trunk offering
A designated extension wishing to transfer an exchange call to another extension may, on making an inquiry call to the extension, find that it is engaged. The designated extension may by dialling an extra digit 1 obtain access to the extension to offer the exchange call. During the time that the designated extension is intruding in this way on an established call a 'warn' tone is automatically applied to that call to indicate the intrusion.

(l) Night service
By operating a night service key which is located on an allocated designated extension telephone the normal extension conditions may be altered, e.g. extensions which are designated by day may be made non-designated by night or vice versa. Similarly extensions which are barred exchange calls by day may be given the facility by night or vice versa. It is also possible under night service conditions to arrange for additional or different call bells to be operated on incoming calls.

(m) Power failure
The power supplies are obtained from a mains-driven power unit. In the event of a failure of the supply the exchange lines are automatically switched to predetermined extensions which then function as normal exchange lines on the public exchange. Any calls which are in progress at the time of the failure are lost. On restoration of the power supply any call in progress from a predetermined extension is maintained until the call is completed.

(n) Inter-switchboard circuits
Two inter-switchboard circuits may be provided to give access to other PABX's or PMBX's over two routes or one route.

The total number of exchange lines which may be provided is reduced by the number of inter-switchboard circuits.

Access to an inter-switchboard circuit from an extension is obtained by dialling a code digit.
Tandem dialling over inter-switchboard circuits is not provided.

(o) Metering
When the PABX 6 is connected to a public exchange with S.T.D. and subscribers private metering facilities, total call meters may be provided for each exchange line and for extensions as required. Provision is made to accommodate these meters in the cabinet. The operation of these meters is dependent upon the application of 50 c/s pulses to the exchange line at the public exchange.

(p) Connection to exchanges
The PABX 6 may be connected to either Automatic, CB, CBS or Magneto exchanges.

(q) Attendant's telephone (optional)
The attendant's telephone consists of a modified Telephone No. 710 mounted on an Answering Unit No. 1A (grey).  This apparatus looked similar to a Planset No. 625 fully assembled.

Introduced in 1966.