A method of making a pyrolytic graphite grid electrode for a high power transmitting tube includes the steps of holding a metallic grid electrode core between two copper blocks, heating the core to 1750.degree.C by passing an electric current through it and passing a carbonaceous gas over the heated core so that graphite is deposited thereon.Because the graphite thickness is reduced towards the copper blocks supporting the core, where the grid is to be used in a high voltage tube annular shields are provided around the supported ends of the grid.