Pentagrid converter
（重定向自Octode）
![Basic heptode-based self-oscillating pentagrid converter circuitsTop: Indirectly-heated variantBottom: Directly-heated variant, which requires the cathode to be grounded](/Images/godic/202501/30/Heptode_Pentagrid0055.png")
![Grids of a 12SA7GT pentagrid converter, showing all five grids](/Images/godic/202501/30/12SA7GT_GridDetail0055.jpg")
![Circuit symbol of a heptode](/Images/godic/202501/30/Heptode.svg0055.png")
![Circuit symbol of a hexode](/Images/godic/202501/30/Hexode_symbol.svg0055.png")
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.