Mining Magneto Wall Telephone
This telephone and the N2980 are specially designed for use in mines and to comply with the recommendations of the Home Office. They have been approved by the Mines Department as being electrically safe for use in fiery mines when used in pairs or in conjunction with an approved bell, indicator or relay, even should the line wires make intermittent contact.
High-grade cast iron case, explosion proof and water-tight, with two wrought iron bars fitted to the back, for fixing purposes.
The outer door, fitted with a slam catch, protects the speaking equipment and generator crank from mechanical damage and dirt.
The ringer gongs are mounted on the top of the case and are protected by a cowl specially designed so as not to deaden the sound.
As it is seldom necessary to open the inner door it is fastened by special headed screw locks a suitable key for the same is provided.
The micro-telephone fitting has an "inset" transmitter, hygienic type mouth-piece and a reinforced handle. It is firmly held on the switch hook by means of protecting pads which bear on the transmitter case thus making the switch more positive ill action.
The generator has two extra large section magnets equal to five of the ordinary size, and a totally enclosed cut-out which is an additional protection against open sparking.
Terminals for the line, extension bell and also for external speaking battery if desired, are mounted in a separate compartment which may be sealed with a compound. A diagram of the connections is supplied.
The apparatus, coil winding and wiring are specially treated to prevent the detrimental and corrosive effects of moisture and gases.
Weight 80 lb.
Dimensions 19 x 12.5 x 10 inches
The N2972 is of similar design.
Taken from the Ericsson Telephone Catalogue, edition No. 26, supplement 1932
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