1. Something that enlarges, or extends: "In electronics, an amplifier uses transistors or electron tubes, which produce an increase of electrical signals.
3. A device that makes sounds louder: "Some amplifiers increase the sound levels of musical instruments."
4. An electronic device that intensifies the magnitude of weak input signals, voltages, or electric currents without changing the characteristics of the waveforms of those signals: "Amplifiers are used in radio and television receivers and in stereophonic sound systems."

"In engineering, amplifiers are used to increase the magnitude of some physical or mechanical devices."

1. An amplifier circuit characterized by low-current drift and input-current offsets, and adequate power and current sensitivities, such that it is capable of measuring extremely low current variations in a circuit.
2. A low-noise amplifier having sufficiently low current drift and other characteristics required for measuring very low currents.

A circuit which uses electron tubes to provide the additional power needed to increase a signal: "An electron-tube amplifier provides the required increase in signal strength."

1. A device that boosts a signal by varying the energy pumped from an electrostatic field into an electron beam traveling down the length of a tube, and then manipulating the beam at either end of the tube.
2. A parametric amplifier in which energy is pumped from an electrostatic field into a beam of electrons traveling down the length of the tube, and electron couplers impress the input signal at one end of the tube and translate spiraling electron motion into electric output at the other end.

An amplifier consisting of an electron-gun modulation system, semiconductor target and output coupling network all within a glass or ceramic envelope.

The semiconductor target is a pair of silicon diodes, each consisting of two metallic electrodes with a pn (positive-negative) junction under the top contact.

A pn junction or a diode (one way valve) is a pn junction with p-type (positive-type) on one side and n-type (negative-type) on the other side.

When a positive voltage is applied to the p-type side (forward bias), it shrinks and overcomes the depletion zone, causing the current to flow from the p-type to the n-type side. When a negative voltage is applied to the p-type of the diode (reverse bias), it increases the depletion zone and prevents current from flowing.

The amplifier operation is based on the fact that a modulated electron beam can control the current in a reverse-based semiconductor junction.