f

Filament connection. Directly heated cathode

h

Heater connection

hct

Heater centre tap connection

k

Cathode. Source of electrons. Normally at ground potential

g1

Control grid. Nearest grid to cathode. Normally held negative of cathode

g2

Screen grid. Normally connected to external positive voltage

g3

Suppressor grid. Normally connected to cathode

g4 etc

Additional grids used in specialist valves such as frequency changers

a

Anode. Normally connected to a high positive voltage

bp

Beam forming plates. In beam tetrodes to focus the electrons

()

Used to indicate the electrode set where several exist in the envelope

s

Internal screen to shield the electrodes

ic

Internal connection. Nothing must be connected to this pin of the valveholder

tc

Top cap connection. Normally the anode(s) are taken to top caps

m

Metalising internal or external to the valve.