A Battery
It is an electric battery used for the purpose of heating the filament or cathode heater of an electron tube.

A Supply
It is a source of power, such as battery, which is used for heating the filament or cathode heater of an electron tube.

Accentuator
It is a circuit or network inserted to give less loss or greater gain to certain frequencies in an audio spectrum like a preemphasis spectrum.

Acron Tube
It is a vacuum tube that resembles an acorn in shape and size and is chiefly used in ultrahigh-frequency electronic devices.

Acoustic Feedback
Also known as "feedback." It is the feedback sound to a microphone from a loudspeaker. It makes a whistling noise by electrical oscillations.

Active
One which acts as a source of electrical energy of a device or system, such as a generator, or it is capable of amplifying or converting voltages or currents like a transistor or diode.

Actuator
It is a servomechanism that provides a certain measured amount of energy to make other mechanism or system operate.

Adcock antenna
It is an antenna which is used to find direction. It consists of a pair of vertical dipoles.

Align
It is the adjustment of two or more components of an electronic circuit inorder to improve the response over a frequency band. It is like aligning the tuned circuits of a radio set for appropriate track throughout its frequency range or aligning a television set for proper wide-band responses.

AM
Short for "amplitude modulation." It is a method of impressing a signal by varying its amplitude on a radio carrier wave.

Amplifier
It is an electronic circuit which takes the input of power from a supply voltage, or voltage source and produces output with increase strength of the original signal. It could be a transistor, a vacuum tube, or an appropriate magnetic device.

Ångström Unit
It is a unit of length measuring the wavelength. It is equal to 0.1 of a billionth of a meter i.e. 1x10-10 meters. Named after a Swedish physicist, Anders Ångström.

Anode Resistance
It is the ratio of a minute change in voltage of the anode of a vacuum tube at a given level of output to the corresponding minute change in anode current.

Anticathode
It is the positive plate of an x-ray tube or other electron tube which serves as the target for electrons coming from the cathode, that causes the emission of high frequency radiations.

Arc-back
It is an undesirable phenomenon, which takes place in rectifier tubes where current flows in the reverse direction from anode to cathode as a result of arcing, limiting the usable voltage of the tube.

Attenuate
It is to decrease the amplitude of an electronic signal.

Attenuator
It is a device which is used to decrease the amplitude of an electronic signal.

Audio Frequency
The normal range of audible sound with a frequency between 15 Hz and 20,000 Hz.

Audion
It is an early type of triode.

Autodyne
It is a type of heterodyne circuit which contains a vacuum tube or transistor acting simultaneously as a detector and oscillator.

Automatic Tracking
It is a radar tracking system where an automatic device make use of the echo signal of a tracked object to keep itself constantly beamed on target and to compute the range of the object.