GB229809A - Improvements in or relating to electric induction heating apparatus, particularly for smelting purposes - Google Patents

Abstract

229,809. Electrical Improvements, Ltd., and Grant, L. C. Dec. 31, 1923. Thermionic generators.-The inductor coil of an induction heating apparatus, particularly for smelting purposes, is energized by a thermionic valve circuit comprising two valves or valve sets having their plates so connected to an alternating supply source that each is operative in turn. As shown in Fig. 1, two valves or sets of valves A, B are used as oscillation generators, their filaments being supplied in parallel by the transformer C, C<1> and their plate circuits energized in opposite phase by the transformer D, D<1>. The centre points of the two transformer secondary coils are connected. High-frequency chokes D<2>, D<3> are connected in the plate leads, and the secondary coil D<1> is shunted by a by-pass condenser D<4>. The frequency of the oscillations is determined by a circuit G, H, one terminal F<2> of the condenser G being connected to the valve grids through a leak resistance F shunted by a condenser F<1>, the other terminal E<a> being connected to the valve plates through blocking- condensers E, E<1>. The filaments are connected to an adjustable tapping on the coil H. The coil H may itself act as the heating inductor, or a separate inductor coil may be connected across the terminals E<2>, F<2>. In a modification, the filaments are connected to the terminal F<2>, and the grids are connected to the filaments through a separate coil coupled to the coil H and shunted by a tuning condenser.