Pentagrid converter
（重定向自Heptode）
![Basic heptode-based self-oscillating pentagrid converter circuitsTop: Indirectly-heated variantBottom: Directly-heated variant, which requires the cathode to be grounded](/Images/godic/202501/17/Heptode_Pentagrid1524.png")
![Grids of a 12SA7GT pentagrid converter, showing all five grids](/Images/godic/202501/17/12SA7GT_GridDetail1524.jpg")
![Circuit symbol of a heptode](/Images/godic/202501/17/Heptode.svg1525.png")
![Circuit symbol of a hexode](/Images/godic/202501/17/Hexode_symbol.svg1525.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.