Cathode heater structure of an electric gun for a cathode-ray tube and method of assembling the heaters

#This invention relates to a cathode heater structure of an electron gun for a cathode-ray tube and a method of assembling the cathode heaters, and particularly a method of automatically positioning and assembling the cathode heaters of an electron gun.

#Generally, an electron gun for a color picture tube comprises a stem 1 for applying voltage from the exterior of the gun, three cathode heaters 3 mounted in a row adjacently to the stem 1 and transversely of the gun through a heater supporter 2, three cathode assemblies 5 containing the respective cathode heaters 3 and supported in a row on bead glasses 12 through a cathode supporter 4, and first, second, third, fourth, fifth and sixth electrodes 6,7,8,9,19,11 disposed in order ahead of the cathode assemblies 5 and secured to the opposed bead glasses 12, as shown in FIG. 1 of the accompanying drawings.

#Here, as shown in FIG. 2, each cathode assembly 5 comprises a tubular cathode sleeve 5a within which the cathode heater 3 is disposed to generate heat, and a cathode cap 5b having on its top thermion emission material such as barium carbonate. Each cathode heater 3 comprises a coiled heat generating portion 3a located in the cathode sleeve 5a of each cathode assembly 5, and a pair of leg portions 3b extending divergently from both sides of one end of the heat generating portion 3a.

#In the accompanying drawings:

#FIG. 1 is a schematic view of a conventional electron gun for a color picture tube;

#FIG. 2 is an enlarged cross-sectional view of three cathode assemblies of the gun of FIG. 1, showing a cathode heater disposed one in each cathode assembly and welded to a heater supporter;

#The invention will now be described in detail, by way of example, with references to FIGS. 5 to 10 of the accompanying drawings.

#Referring to FIGS. 5 and 6, the present invention provides a method of assembling in place three cathode heaters 3, which are disposed on in each of three cathode assemblies 5 arranged in a row transversely of an electron gun, by using a heater supporter 2 having a plurality of pairs of guide grooves 2b formed therein to correspond in number to the number of the cathode assemblies 5 and the guide and position leg portions 3b of the cathode heaters 3. The guide grooves 2b of the heater supporter 2 are disposed at predetermined intervals corresponding to the distances S between the longitudinally extending lines passing through the centers of the R, G and B electron beam passage apertures of electrodes (not shown). Each guide groove has a deepest bottom at its central portion. The shape of each guide groove is not restricted to a triangular shape as shown in FIG. 5, but may be any of various shapes including a single circular arc 2c as shown in FIG. 8a and a multiple arc 2d comprised of a plurality of circular arcs as shown in FIG. 8b.

#The cathode heater 3 on the present invention has engaging portions 3c formed by bending the ends of the leg portions 3b to be engaged with the guide groove 2b of the heater supporter 2. At this time, the bending positions of the leg portions of the cathode heater are determined in design in consideration of the distance G between the leading of a heat generating portion 3a of the heater and the deepest central bottom of each guide groove 2b of the heater supporter.