GEC No. 680
IRONCLAD MAGNETO TELEPHONE
This instrument is designed to comply with the regulations governing the use of electrical equipment in mines. An explosion-proof cast iron case finished in black stove enamel encloses all wiring and apparatus and is so proportioned as to offer the minimum internal space for the accumulation of gas. The component parts include a 5-magnet generator, high resistance ringer, solid back transmitter and " Bell " type receiver.
The generator is driven through a flexible coupling which ensures reliable operation of the contact springs and minimises wear on both the generator and handle hearings. For the connection of the earpiece to the receiver, which is permanently fitted inside the case, a flexible metal tube is employed.
The generator shaft, bell armature and receiver tube operate through glands in the case, and machined flanges one inch wide ensure a flameproof and watertight joint when the front cover is bolted in position. Two dry cells for the local speaking battery are enclosed in metal containers secured to the rear of the front cover.
A connecting box forms an integral part of the case and is provided with a separate cover so that connections may be made without opening the instrument proper.
Taken from the GEC Telephones and Switchboards (Manual and Automatic) Catalogue No. 11 (Circa 1936)
Last revised: July 27, 2012