Induction circuit for telephone bell electromagnet - has yoke passing through coil and made of thermoplastic synthetic resin contg. evenly distributed ferromagnetic particles

摘要

The induction circuit, for an electromagnet or for the bell of a telephone set, has a magnetic yoke passing through the coil and extending to form a closed magnetic circuit. At least that part (3) of the yoke that passes through the coil is made in one piece from a thermoplastic synthetic resin containing evenly distributed ferromagnetic particles, e.g. iron fillings. This part of the yoke is designed to act as a coil former and is also subjected to a permanent magnetic bias.