Pentagrid converter

The pentagrid converter is a type of radio receiving valve (vacuum tube) with five grids used as the frequency mixer stage of a superheterodyne radio receiver.

The pentagrid was part of a line of development of valves that were able to take an incoming RF signal and change its frequency to a fixed intermediate frequency which was then amplified, and detected in the remainder of the receiver circuitry. The device was generically referred to as a frequency changer or just mixer.