Electron tube is one of the earliest electrical signal amplification devices.The cathode electron emission portion, control gate, acceleration gate, and anode (plate) leads enclosed in a glass container (usually a glass tube) are welded to the tube base.The electric field is used to inject the electronic modulation signal to the control grid in the vacuum, and the signal data of different parameters after amplification or feedback oscillation are obtained at the anode.Early applied to electronic products such as television, radio amplifier, in recent years gradually be replaced by the amplifier and integrated circuit of semiconductor materials, but in some high fidelity audio equipment, still using low noise and high stable coefficient of tube as the audio power amplifier device (Hong Kong person use vacuum tube power amplifier for "bravery").