A one-piece table instrument is at all times preferable to one made up of two or more parts and the magneto type of telephone has been the most difficult to combine in a neat form.
Hitherto telephones for magneto working have been heavy and cumbersome on account of the size of the generators available. With modern magnetic materials a new and highly efficient magneto generator of very small size and weight has been produced. By incorporating this new generator into our already popular moulded case an instrument of excellent symmetry, light and efficient, is provided for magneto working.
The internal apparatus is mounted on a metal base plate which can be completely detached from the case. The apparatus comprises, induction coil, generator, ringer and gongs, switch spring-set and cord connecting block, space being also provided for a condenser when required.
Telephone comprises of:-
The sliding tray fitment is not practicable on this telephone.
Mining Type - A similar instrument intended solely for use on the mine surface under cover, as in offices, etc., can be supplied. Code No. N2121Z.
Supplied worldwide and to GEC.
Taken from the Ericsson catalogue, edition No. 49
The N2121A50T has a chromed metal line cord retaining plate.
This telephone is not conventionally wired and the bell ringer is directly across the line with no capacitor. Because of this a 1.8uf capacitor must be connected to terminals 1 and 2 in the telephone and any link between 1 and 2 removed.
This telephone requires a battery for transmission. A 3 volt battery (2 x U2) should be connected to terminals 1 (positive) and 10 (negative) in the telephone.
The line is connected to terminals 1 and 3.
These telephones were also available
tropicalised and can be identified by the suffix "T" at the end of the model
Diagram N75142 for Telephone N2121A22 (dated 1949)
Diagram N57255 issue 3 for Telephone N2121A3
MAGNETO, RURAL PARTY LINE
These robust moulded telephones are used on code ringing party lines connected to a magneto exchange. They have a non-locking push button which is pressed only while operating the generator to call the exchange. It is not used when calling another subscriber on the same party line.
A capacitor is included in the circuit to prevent the line being loaded due to a handset not being replaced.
The appearance and construction of these telephones are similar to those of the standard N2121A and N2204 type sets, except for the shape of the handset and the inclusion of the push button key.
The external wires enter the wall instrument through a hole in the back plate, and terminate at screw connections on the removable internal equipment unit. Connections to the table instrument are via a moulded desk terminal block and cord.
All internal wiring is insulated with P.V.C.
The standard colour of these telephones is black, but they can also be supplied in ivory, P.V.C. insulated, nylon braided cords can be supplied if specified.
Wood cased telephones, similar to that illustrated on the opposite page but with the addition of a plunger key, are available for situations where a specially robust set is required.
The circuits of any of these telephones can be arranged to suit special operating schemes. Generators and ringers of other resistances can be provided.
Cells for transmitter battery are not supplied unless ordered.
See also N2204.
Magneto rural phones by British Ericsson are generally found in Canada and New Zealand.
Taken from the Ericsson catalogue, edition No. 55
INTRINSICALLY SAFE WALL TELEPHONE
This telephone is for office use in collieries and in the petroleum industry. It may safely be connected with the underground circuits in mines and used in parallel with other intrinsically safe telephones, as stipulated in the Telephone and Signalling Orders.
The design is similar to that of the conventional moulded plastic table instrument which has become popular by virtue of its reliability and convenience for maintenance.
The easing is shaped to form a robust cradle for the handset, which rests on two plungers forming part of a smoothly operating roller-plunger movement specially designed to minimise friction and wear.
The internal components are mounted on the metal baseplate, which has non-slip rubber feet and is attached by captive screws to the case, thus the latter can be removed to expose the parts for maintenance. The components include anti-side-tone induction coil, ringer, 'alnico' generator and capacitors.
All connecting wires are insulated with p.v.c.
Handset and desk cords terminate at screw connections. These cords are normally rubber insulated and cotton braided, but p.v.c. insulated, nylon braided cords can be supplied when specified.
The handset is of standard pattern and proven efficiency. It incorporates an inset transmitter and detachable receiver inset.
A moulded desk terminal block with screw connections is provided for terminating line and battery wires. Batteries are not supplied unless ordered.
A copy of the wiring diagram is fixed inside the telephone.
Type No. N2121Z
Weight 7.5 lbs. (3.40kg.)
N2121Z supersedes the N2120.
Introduced circa 1949.
Certified for mine surface use only - Certificate T/Tel 82.
Taken from the Ericsson catalogue, edition No. 55 & 60
This telephone is not conventionally wired and the bell ringer is directly across the line with no capacitor. Because of this, the bell wire tag connected to the front of terminal 2 must be removed and a 1.8uf capacitor connected between this tag and terminal 2. On the back of terminal 2 there is a black wire - this also needs to be removed and the end insulated.
This telephone requires a battery for transmission. A 3 volt battery (2 x U2) should be connected to terminals 9 (negative) and 10 (positive) in the telephone.
The line is connected to terminals 3 and 10.
Diagram N73116 for Telephone N2121Z (dated 1949) and N2121Z20
As N2121 but without the press button in front of the handset.
Last revised: July 31, 2022