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How valve amplifiers work

How they work

An electronic amplifier is a device for increasing the power of a signal. It does this by taking power from a power supply and shaping the output to match the input signal. This process invariably introduces some noise and distortion into the signal, and the process cannot be 100% efficient - ¯amplifiers will always produce some waste heat. An idealized amplifier can be said to be "a piece of wire with gain", as the output is an exact replica of the input, but larger.

Different designs of amplifier are used for different types of applications and signals. We can broadly divide amplifiers into three categories - ¯small signal amplifiers, low frequency power amplifiers and RF power amplifiers. Each of these calls for a slightly different design approach, mainly because of the physical limitations of the components used to implement the amplifier, and the efficiencies that can be realised.

Amplifiers can be implemented using transistors of various types, or vacuum tubes (valves). Other more exotic forms of amplifier are also possible using different types of devices, but these will not be discussed in detail here to avoid complicating the picture too much. Such exotic amplifiers are often used for microwave or other extremely high frequency signals.