Abstract: The invention is a method of manufacture of a cylndrical electrode such as a thermionic cathode comprising an array of helical filaments. The method comprises the step of placing the array, attached to its support electrodes which are fixedly mounted to a common subassembly support, inside a close-fitting refractory dielectric cylinder and heating the filament assembly by passing current through the filaments. The filament assembly expands to contact the form. On further heating it is plastically deformed to form a perfect cylindrical shape. After cooling and shrinking, it is removed from the form.