amplifier
device that can increase the power of a signal (not necessarily electronic)
electronic amplifier
electronic circuit or component that increases the level of incoming electrical signal (not necessarily audio)
optical amplifier
device that amplifies an optical signal
Multistage amplifier
amplifier consisting of two or more simple amplifiers connected in series
Cascade amplifier
Cascading amplifier
crossed-field amplifier
specialized vacuum tube used as a microwave amplifier