TELEPHONE No's N1636 & 1637

C.B. Intercommunication Telephones

n1636c.jpg (6379 bytes) n1637c.jpg (6282 bytes)
N 1636C Type   N 1637C Type

One of the most effective means of inter-office communication where a relatively small number of lines is required, is the intercommunication telephone system, as immediate connection is established on the pressure of a button ; no operator or automatic dial being necessary. It may also be installed in large establishments as a supplementary system for the use of executives.

For many years our intercom telephones have been markedly popular by reason of their efficiency and reliability. In conformity with our progressive policy, we have redesigned these telephones on lines more in keeping with current requirements, and we are confident that they will have instant appeal, as they embody the simplicity of outline favoured for the modern office, while still retaining the proved advantages of their predecessors.

The instruments have moulded cases in fadeless black or ivory, and ivory moulded push buttons; thus, as there are no external metal parts to become tarnished, a lasting "new" appearance is ensured.

The casing is loose-hinged, and fastened by one screw, to a strong plastic base plate carrying the internal components which are therefore accessible for maintenance when the. case is lifted off.

These components include the push button mechanisms mounted in pre-wired units of five, each unit bearing a paper strip printed with the appropriate numbers. The mechanisms are protected by a moulded panel having apertures for the buttons and designation strips, the latter being covered by convex transparent plastic windows which are bonded in and give prominence to the printed numbers.

Highly satisfactory reproduction of speech is given by the inset transmitter and electromagnetic receiver incorporated in the moulded micro-telephone, the cord from which enters the case through a rubber protector arranged to accommodate also the desk cord of the table instrument.

A moulded desk terminal block is supplied for the connection of the line wires to the table set, whilst the wires to the wall set enter through a hole in the baseplate and are connected to screw terminals. A combined instruction/directory card is supplied with each telephone.

To make a call, lift the micro-telephone and press the appropriate button to its full extent. If the called number is free, a buzzing tone will be heard in the receiver, indicating that the required person is being called.

A button, having been pressed, is retained in an intermediate position during the call, and is automatically released when the micro-telephone is replaced or another button is pressed; successive calls can therefore be made without replacing the micro-telephone.

Incoming calls operate a buzzer in the instrument. To reply, it is necessary only to lift the micro-telephone and speak.

The system is operated from a central battery, or via an eliminator when an a.c. supply is available. In either case, the best results are obtained when the source of supply is as near as possible to the centre of the system.

For a maximum line length of 2,000 feet (the approximate economic limit) a battery of nine dry or inert cells is usually adequate. Where the distance is less, the battery is proportionately smaller.

If a station is remote from the main installation, an N1112A type call and reply telephone is usually supplied as a subsidiary to the nearest intercom station. The call and reply telephone can be rung from any station but can only call the one to which it is subsidiary. This arrangement effects a considerable saving in cable costs.

For a complete installation, junction boxes, cells with boxes (or an eliminator) and cable are supplied.

The type of cable recommended for a particular installation is specified in the quotation and comprises suitably insulated 9, 14 or 19, No. 23 s.w.g. copper conductors, respectively, for the 5, 10 or 15-line systems.

Code No.   Type   No. of Lines
N1636A   Table   5
N1636B   Table   10
N1636C   Table   15
N1637A   Wall   5
N1637B   Wall   10
N1637C   Wall   15

Dimensions (excluding h.m.t.): 6.5" x 8.75" x 4.1" (168 x 222 x 105 mm)
Total weight : 4.6 lb. (2.1 kg.) max.

Note - Orders for telephones should specify the Type No. and colour ; black or ivory.

Taken from the Ericsson catalogue, edition No. 49

Introduced around 1953 - superseded N1620 - N1627


INTERCOM. TELEPHONES TYPES N.1636, N.1637, N.1732, N.1733

These instructions cover:-
1.1 General Maintenance.
2.1 Adjustment of push-button keys.
2.2 Adjustment of cradle switch.
Part Nos. referred to are shown on the relevant equipment drawings.

The simplicity of construction and operation of these telephones, coupled with the fact that the materials used are not liable to corrosion or excessive wear, ensure long, reliable service with minimum attention. The instruments are subjected to stringent tests in the factory and, provided that they are treated with reasonable care, should require no routine maintenance apart from a periodic check of the associated batteries to ensure that the output is satisfactory.

Experience has shown that while these telephones are working efficiently they are best left undisturbed.

The majority of faults which occur have been found attributable either to the deterioration of batteries or to low insulation of the cable brought about during structural alterations or through some building fault, therefore these possibilities should first be investigated, unless the source of the trouble is obvious, e.g. a sticking push-button or cradle switch plunger.

However, these are unlikely contingencies in the reasonably dust-free atmosphere of the average office.  In order to cover every eventuality, the following information for the adjustment of push-button keys and cradle switch springs has been extracted from our factory specification.

Relevant Drawings:
For Telephones N. 1636 or N.1637, Drawing N.78795.
For Telephones N. 1732 or N.1733, Drawings N. 78793 (or N.78794) and N. 78795.

  1. All screws should be tight. Screw, part 28, to be sealed with Araldite to part 21.
  2. In latched position, each plunger should be free to move slightly before lifting latch plate 8.
  3. The plunger should freely lift latch plate from the latched position to a position not more than .048 in. from edge of frame (see Fig. 1).
  4. Apply alcohol dag along inside and outside faces of latch plate, on linking arm, on inside edge of moulded plunger insert and on ends of pin 6.
  5. Tension of spiral spring 7 should hold short arm firmly against, but not projecting above, edge of plate 4.

Spring Tensions
Note:- The part must not move when gauge is set at the specified low limit, but should begin moving at any tension above this, up to the high limit.

  1. Plunger Springs. With plunger fully depressed, tension at tip of springs 14 and 15 should be 60-80 gms.
  2. Latch Plate Spring (Fig.2). With plungers unoperated and gauge tip applied to bottom of linking arm, the tension on latch plate 8 should be 3 0-50 gms. With any plunger operated (latched) and gauge applied as above, latch plate must not lift from plunger at less than 100 gms pressure.
  3. Master Station Springset. Tension of all moving springs against back spring should be 20-30 gms measured at tip. Contact clearance:- .010 in. minimum.  Moving springs must make contact on operation and have visible "follow".

Relevant Drawing, N.82934.

  1. All screws should be tight. Screws 19 and 16 fixing cradle brackets and latch spring to be sealed with Araldite at screw end.
  2. Bracket part 7 should Latch behind latch 5 before 'ringing" position is reached. Bracket 8 should release 7 before full depression. All movements should be free.
  3. Bracket parts 13 and 14 should move freely over pins in bracket part 8.
  4. Alcohol dag to be applied to all bearing surfaces, particularly parts 1, 5, 11, 13 and 14.
  5. Brackets 13 and 14 to be square against frame when held in vertical position by spring 10.

Spring Tensions
Note:- The parts mentioned in (a), (b) and (c) must be free, to ensure true reading of tensions.

  1. With latch plate 5 held disengaged from inner bracket 7, tension exerted by return spring 9 should be such that 65-75 gms pressure applied to bracket 7 immediately adjacent to plunger is necessary just to move bracket.
  2. With springset3 removed and bracket 7 fully depressed a force of 50-60 gms applied adjacent to plunger should be necessary to press down bracket 8.
  3. With bracket 7 fully depressed, tension of latch plate spring 6 should require a force of 10-15 gms applied to tip of latch plate 5 just to move it away from bracket.
  4. Locating screws of switch parts 3 and 4 to be varnish sealed during final adjustment. Locating buffer must be within .005 in. of plate.

Springset Tensions (see Fig. 3)

  1. With cradle bracket 8 fully depressed, buffer springs 5 and 8 should exert a pressure of 20-35 gms on springs 4 and 7 respectively, with visible "follow".. Contact gaps between springs 3 and 4 should be .010 -.025 in.
  2. With all plungers disengaged from springset, contact gap between springs 1 and 2 should be .010 - .020 in., and roller springs 4 and 7 should exert a pressure of 20-35 gms on buffer springs 3 and 6, measured at the contacts.
  3. Actions (a), and (b) above, will automatically ensure correct gap of .008 - .020 in. between contacts of springs 4&5 and 7&8.
  4. With cradle brackets depressed to within .072 in. of their full travel, all springs of the main springset should be operating.

    Ringing springs
  5. With part 7 latched in the "conversational" position, spring 10 shall be adjusted so that the contact gap between springs 9 and 10 is .005 - .010 in. with spring 9 tensioned against ringing plunger. This will result in visible "follow" on spring 10 when part 7 is in ringing position.
  6. With cradle brackets in the "handset off" position, spring 9 adjustment should provide for a contact gap of .010 - .025 in. between springs 9 and 10.


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Last revised: October 03, 2019