Transistor radio

During the Thousand Year War on Skaro, the Fourth Doctor observed that the discovery of a soldier with a uniform partly made of animal skins with a combat jacket made of "modern synthetic fibre" was like finding the remains of a Stone Age man with a transistor radio. (TV: Genesis of the Daleks)

Susan Foreman possessed a transistor radio, which she used to play music. (TV: An Unearthly Child, PROSE: Doctor Who and an Unearthly Child, AUDIO: Hunters of Earth)