Class A Tuned Amplifier – Characteristics, Working & Applications

Class A tuned amplifiers are analog electronic circuits that are designed to amplify a narrow range of frequencies around a particular resonant frequency.

Characteristics of Class A Tuned Amplifier

  • Linear operation mode
  • High gain
  • Low noise
  • Narrow frequency response


Class A tuned amplifiers consist of an active element, such as a transistor or vacuum tube, and a resonant circuit, which is typically a tuned LC circuit. The active element amplifies the input signal and passes it through the resonant circuit, which amplifies the signal further and filters out unwanted frequencies.

The active element is biased so that it operates in the linear mode, which means that it is always conducting current. This results in high power dissipation and low efficiency. However, this is not a significant drawback in applications that require high-fidelity amplification.


The specifications of a Class A tuned amplifier would typically include:

  • Frequency Range: The range of frequencies over which the amplifier is designed to operate effectively.
  • Gain: The amplification factor of the amplifier, which is the ratio of the output signal amplitude to the input signal amplitude.
  • Tuning: The amplifier is tuned to a specific frequency or a narrow range of frequencies using tuned circuits, such as LC (inductor-capacitor) circuits.
  • Output Power: The maximum power that the amplifier can deliver to the load.
  • Efficiency: Class A amplifiers are known for low efficiency, as they continuously consume power even when there is no input signal.
  • Linearity: Class A amplifiers are highly linear, meaning they preserve the shape of the input signal faithfully in the output.
  • Noise Figure: This measures the amplifier’s contribution to the overall noise in the system.
  • Input and Output Impedance: The impedance values that the amplifier presents to the input and output circuits, which should be matched to optimize signal transfer.
  • Biasing: Class A amplifiers require a proper biasing arrangement to ensure that the transistors or tubes operate in their linear region.
  • Distortion: The level of distortion introduced by the amplifier, which should be minimized for accurate signal reproduction.
  • Physical Dimensions: The physical size, weight, and packaging of the amplifier.
  • Heat Dissipation: Class A amplifiers generate significant heat due to their continuous operation, so cooling mechanisms are important


  • Audio amplifiers
  • Radio receivers
  • Communication systems

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