Means for positioning a heating element with a thermionic cathode structure

Claim 1

In a cathode ray tube electron gun structure utilizing at least one thermionic end-emissive tubular cathode having a closed terminal end with electron emissive material exteriorly disposed thereon and accommodating therein a heating element having two separate connective extremities projecting from the open end of said cathode, means for positioning said cathode heating element within said cathode to effect predetermined orientation of said heating element therein, said means comprising: fixed heater support means spatially rellated to the open end of said cathode structure in a manner to provide separate support for each of said heating element connective extremities; and at least one heating element positioning device formed of a continuous strip of bilaminate metallic material of predetermined flexure performance shaped to have an upper attachment portion at one end thereof and a lower attachment portion at the opposite end with an acutely curved bend of bilaminate strip forming a partial loop of said material therebetween, said device having one attachment portion affixed to a respective connective extremity of said heating element and the other attachment portion to one of said fixed heater support means, said bilaminate material being formed of a first lamina of active alloy material contiguously metallurgically bonded along a common interface to a second lamina of a passive alloy material, said active alloy material upon being subjected to a predetermined temperature undergoes a metallurgical phase transformation effecting a volume change thereof, said passive material remaining in a substantially stable single metallurgic phase state throughout a temperature range wherein said predetermined temperature is included, said predetermined temperature being above the temperature encountered in toto by said bilaminate material during fabrication of said heater positioning device and the incorporation thereof into said electron gun structure, said predetermined temperature being a thermal level encountered during subsequent tube processing, said bilaminate heater positioning device having a formed primary shape effected prior to incorporating into said electron gun structure, the active lamina portion of said primary shaped positioner upon reaching a predetermined temperature during tube processing transforms to said metallurgical phase thereby modifying the shape of said bilaminate positioning device to form a secondary structural shape thereby imparting a positional movement to said heating element within the cathode to effect a positive and sustained location of said heating element therein.