Mostyl Crystal set radio receiver, complete with BBC logo, manufactured by Gramostyles Ltd of Birmingham between 1923-1926.

The crystal set was a simple radio receiver which did not need any power to make it work. It only received AM, amplitude modulated, signals. The crystal, with a point contact, called a cats whisker as that was what was sometimes used, on its surface, created a diode action rectifying the carrier wave so making it possible to hear the audio signal which was modulated onto it.