Abstract: An induction heating generator consists of a Hartley oscillator employing a tank circuit, including the induction heating coil, disposed in series with the emitter-collector circuit of the transistor. A bias circuit consisting of the parallel combination of a capacitor and diode is connected to the base and the feed-back voltage to the base is generated by a tickler coil. In the absence of oscillations the base is biased for class A operation and the resulting feed-back current charges the bias circuit to shift the operating point to class C operation. The bias voltage is decreased when the tank coil is loaded, lowering its impedance. This maintains stable operation of the oscillator independent of variations in the load. When the coupling between the load and the inductor is so great as to overload the oscillator, the bias circuit prevents oscillation.

Abstract: Meals for institutional feeding are arranged on trays in a central commissary with hot and cold food portions in separate containers. The containers for the hot items have bases formed with metallic plates and thermally insulated covers with internal metallic heat radiators. The trays are arranged in stacks in a refrigerated transport cart having spaced shelves which extend between the trays and include induction heating coils which produce heat generating currents in the metallic elements of the bases and covers of the hot food containers, heating these food portions while the other items are refrigerated. The hot food containers are provided in a variety of configurations each of which is heated at a different rate by the coils so the serving temperature of the food is determined by the type of its container.