High-frequency furnace for inductive heating

930,376. H.F. furnaces. PHILIPS ELECTRICAL INDUSTRIES Ltd. Dec. 18, 1959 [Dec. 22, 1958], No. 43097/59. Class 38 (4). A thermionic oscillator feeding a high-frequency furnace which supplies a low-resistance heating coil 13 through a transformer comprising a coupling coil 11 and a circuit coil 3, 31, is arranged to supply also a high-resistance heating coil 16. The circuit coil may be in two parts with the coil 16 connectible between, and two capacitors 4, 41 may be arranged so that some point in the coil 16 is at earth potential. A switch 18, 19 in one position is arranged to shunt a pair of terminals 17 and in another position to shunt the coil 13 and connect the coil 16 in circuit. The switch may have a third position whereby both coils are in circuit at once. In another arrangement the coil 11 may be in two parts each associated with a coil 3 or 31, the two parts being connectible in parallel or series. The inductance of the coil 13 may be between 0.02 microhenrys and 1 microhenry and the inductance of the coil 16 may lie between 1 microhenry and 40 microhenrys.