Subclass 1/142: Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps (details of electron-optical arrangements or of ion traps H01J 3/00) Main electrodes Solid thermionic cathodes characterised by the material with alkaline-earth metal oxides, or such oxides used in conjunction with reducing agents, as an emissive material