A triode(from three electrodes) was the vacuum tube
equivalent to a transistor. It consist of a vacuum tube
with an anode, a control grid and a cathode filament.
simplified buildup
O-----. : |
) : |
( : |
Glow ) : |
current ( : |
) : |
( : |
) : |
O-----' : |
| | |
O O O
C G A
Legend
C Cathode
G gate/grid
A anode
To the cathode filament a glow current is applied, this
is because electrons is more 'willing' to leave a heated
electrode. By applying a voltage to the grid, a flow of electrons
to the anode is created. And by changing the grid voltage,
the flow can be controlled.
The triode is still used in some amplifiers, but
due to lower efficiancy it has mostly been replaced
by transistors. | 
