A linear amplifier increases power into the electrical load, the source from which the output of sound is delivered. The amplifier carries a signal, such as a radio signal, over a larger distance, allowing for distribution of the signal to a wider audience.
A linear amplifier is a specific type of amplifier that affects radio waves. Linear amplifiers can contain either vacuum tube or solid-state technology. Broadcasters concerned with reaching a wider audience over a larger area typically use the solid-state amplifier, as it is better suited for high frequency. The vacuum tuber amplifier is better suited for the amateur radio operator who uses the amplifier on a limited basis.
Solid-state amplifiers are generally more reliable than vacuum tube amplifiers. Vacuum tubes are a somewhat archaic technology, and can experience various mechanical and technical issues.