| Term | Definition |
|---|
| A Power Supply | A power supply device providing heating current for the cathode of a vacuum tube. |
| Alternating Current | A current, the direction of which reverses at regular recurring intervals, the algebraic average value being zero. |
| Amplification Factor | A measure of the effectiveness of the grid voltage relative to that of the plate voltage in affecting the plate current. |
| Amplifier | A device for increasing the amplitude of electric current, voltage or power, through the control by the input power of a larger amount of power supplied by a local source to the output circuit. |
| Anode | An electrode to which an electron stream flows. |
| Antenna | A conductor or a system of conductors for radiating or receiving radio waves. |
| Atmospherics | Strays produced by atmospheric conditions. |
| Attenuation | The reduction in power of a wave or a current with increasing distance from the source of transmission. |
| Audio Frequency | A frequency corresponding to a normally audible sound wave. The upper limit ordinarily lies between 10,000 and 20,000 cycles. |
| Audio-Frequency Transformer | A transformer for use with audio frequency currents. |
| Autodyne Reception | A system of heterodyne reception through the use of a device which is both an oscillator and a detector. |
| Automatic Volume Control | A self-acting device which maintains the output constant within relatively narrow limits while the input voltage varies over a wide range. |