Systems 1 and 3 described in the following pages represent simple exchange connected extension plans, providing a low-cost dependable telephone service. They are particularly suitable for small organisations, and fulfil all main requirements for extension plans covering secretarial, parallel-extension, external-extension and dual exchange line working. Connection can be made to any type of automatic or C.B. exchange, public or private.
The Plan Etelphone
The handset cord is the coiled extensible type, sheathed in p.v.c. and coloured to match the telephone. Instrument colour matching also applies to the desk block and its associated line cord, provided the number of line-cord leads does not exceed six. In excess of this number the desk block and line cord are provided in elephant-grey. A carrying handle and performance regulator unit are included in the instrument.
The dial (when fitted) has a clear plastic finger plate, standard numbering (i.e. 1 to 0) and transmits 10 p/s with 2:1 break/make pulse ratio. Alternatively, dials can be supplied with any desired numbering, pulse speed and ratio.
Manual release by means of an integral sliding cap. (Note: a press button with this action provides simple on/off switching for such purposes as instrument bell control.)
A fifth press button is incorporated to the right above the dial when transfer or
recall facilities are required.
Audible signalling is by a.c. bell and buzzer. Either or both units may be incorporated in the telephone according to the extension- plan requirements and can be supplemented by similar wall mounted units. The a.c. bell signals incoming calls from the main exchange. In-built transistor ringing generators provide a.c. ringing current for external-extension signalling. The d.c. buzzer signals calls between internal extensions situated in or near the same building.
Line limits between internal extensions with 6V local signalling allow for loop resistances of up to 1000 ohms, this being equivalent, for example, to approximately 200ft (61m) of 6.5lb/mile (0.5mm) conductor. Between an external extension and the main exchange the loop resistance may be up to 1000 ohms.
PLAN-ETELPHONE TYPE 1
This Plan system is suitable for up to two executives served by one exchange line and requiring incoming calls to be filtered at an intermediate (secretarial) point. Basically similar to BPO plans 105 and 105A, it provides two significant service features: (a) the automatic holding of exchange calls at the secretary's intermediate telephone and (b) direct access to the exchange line from the executives' extension telephones, dispensing with the need for secretarial assistance.
The intermediate (secretary's) telephone is simple to operate. It incorporates four press buttons. The outer two, designated RING 1 and RING 2, are used for selective calling of extensions; the inner two, designated EXCH and EXTN, are for switching functions. Exchange calls are answered by pressing the EXCH button and then offered to either extension as required by first pressing the EXTN button, followed by the appropriate RING button.
The exchange call is held automatically while the call is offered, and is transferred automatically when the handset at the intermediate telephone is replaced. Should the extension user not accept the call, the EXCH button is re-pressed to permit return to the exchange line.
If the intermediate instrument is temporarily unattended, an exchange call can be signalled at either extension on manual release of the bell on/off press button, and the call accepted. During exchange calls at either extension, the 'engaged' lamp glows at the intermediate.
Power and cabling
PLAN-ETELPHONE TYPE 2
This is a simple system, suitable when one exchange line is required to serve several internal extensions.
All exchange calls are answered at the main telephone and passed to the required extension.
The main telephone is available with either 4 or 8 press buttons and an AC bell.
The extension telephones incorporate a DC bell.
Plan-Etelphone Type 3
This Plan system is suitable for users with one exchange line serving two locations some distance apart; for example, a shop and associated warehouse. It consists of an intermediate and an external-extension telephone connected by a 2-wire line. Bothway signalling between intermediate and extension is by in-built transistor ringing units.
The loop resistance between the external extension and tie main exchange can be up to 1000 ohms. At the intermediate telephone, four locking press buttons are provided for the following switching and signalling functions:-
Intermediate to exchange with a.c. buzzer across the extension line.
Extension cannot overhear.
Intermediate to extension with a.c. bell across the exchange line.
Information call with the exchange line held. The exchange caller cannot overhear.
Extension to exchange direct. Calls can be secret or non-secret from the intermediate.
Incoming exchange calls are normally answered at the intermediate, and are held when offered to the extension. The call is transferred automatically when the EXTN-EXCH button at the intermediate telephone is operated. Should the extension user not accept the call, the intermediate user may return to the exchange line by pressing the EXCH button. During extension-to-exchange calls the 'engaged' lamp glows at the intermediate.
Power and cabling
Taken from the Plessey Telephone Catalogue (1971)
According to the code book there were 16 types of N1906 and to make matters worse, there were variations on these. Most of the types came in all standard seven colours and were shipped worldwide.
All types first introduced in 1960.
Last revised: December 10, 2019