Grid - An intermediate electrode between the Cathode (or Filament on a direct type) and the Anode (Plate). Types of grid include "Control" (g1) which controls the electron flow, "Screen" (g2) which is an electrostatic screen between Anode and Control grid improving RF performance, "Suppressor" (g3) which suppresses secondary emission between the Anode and Screen grid. The Control g1 is usually more negative than Cathode, Screen g2 is usually at a higher voltage than Anode and Suppressor g3 usually at Cathode voltage. Physically the grids can be helical fine wire, a mesh, rods, plates. Rods or Plates need an electron beam.