Filament connection. Directly heated cathode.
Heater centre tap connection.
Cathode. Source of electrons. Normally at ground potential.
Control grid. Nearest grid to cathode. Normally held negative of cathode.
Screen grid. Normally connected to external positive voltage.
Suppressor grid. Normally connected to cathode.
Additional grids used in specialist valves such as frequency changers.
Anode. Normally connected to a high positive voltage.
Beam forming plates. In beam tetrodes to focus the electrons.
Used to indicate the electrode set where several exist in the envelope.
Internal screen to shield the electrodes.
Internal connection. Nothing must be connected to this pin of the valveholder.
Top cap connection. Normally the anode(s) are taken to top caps.
Metalising internal or external to the valve.