Low power heater

Claim 1

A HEATER-CATHODE ASSEMBLY FOR AN ELECTRON GUN OR THE LIKE COMPRISING AN INVERTED CUP-SHAPED CATHODE HAVING A SIDE WALL, A TRANSVERSE TOP WALL SURMOUNDING SAID SIDE WALL FOR SUPPORTING AN EMISSION SURFACE OF THERMIONIC ELECTRON EMISSIVE MATERIAL, A CONTINUOUS ELONGATED CONDUCTIVE HEATING ELEMENT ARRANGED IN A COIL, SAID COIL BEING EMBEDDED WITHIN AN ENCAPSULATIION OF ELECTRICALLY INSULATIVE THERMALLY CONDUCTIVE MATERIAL, SAID ENCAPSULATION BEING DISPOSED WITHIN SAID CATHODE WITH THE AXIS OF SAID COIL EXTENDING GENERALLY PARALLEL TO SAID TOP WALL, THE LOWER COURSES OF THE TURNS OF SAID COIL BEING DOWNWARDLY SPACED FROM THE UPPER COURSES OF THE TURNS OF SAID COIL NO MORE THAN THE SPACING OF SAID UPPER COURSES FROM THE UNDERSIDE OF SAID TOP WALL, THE SIDES OF SAID ENCAPSULATING BEING INWARDLY SPACED FROM THE SIDE WALLS OF SAID CATHODE CUP TO MINIMIZE HEAT TRANSFER FROM SAID ENCAPSULATION TO THE SIDE WALLS OF SAID CATHODE, THE TOP OF SAID CAPSULE BEING IN INTIMATE HEAT TRANSFERRING CONTACT WITH THE UNDERSIDE OF THE TOP WALL OF SAID CATHODE AND CONDUCTORS EXTENDING FROM SAID COIL EXTERNALLY OF SAID ENCAPSULATION AND FORMING LEADS FOR ENERGIZING SAID HEATING ELEMENT.