Power tube cathode grid - containing shadow grid material in holes produced by laser beam

摘要

The parent Patent No. 2535467 described a method of producing a cathode grid assembly for grid controlled power tubes with a shadow grid formed by filling out recesses in the emission layer. Instead of producing these holes by spark erosion, it is now suggested to use a laser, preferably a neodymium YAG laser for this purpose. The beam of a neodymium YAG laser is used to remove the emission material from the layer (2) in a certain pattern. The produced holes are filled with a shadow gat material (3) such as molybdenum or tungsten, and coated with a material (4) to suppress the electron emission, e.g. zirconium or carbon. It was found that the dielectric liquid needed for spark erosion contaminates the cathode emission material. Spark erosion also opens the pores of thin material to an undesirable degree. The new method prevents all this.