Heptode

an electron tube with seven electrodes: a cathode, a plate, and five grids, of which two are control grids, two are screen grids, and one is a suppressor grid. Heptodes are used chiefly for mixing and converting high-frequency electrical oscillations in superheterodyne radio receivers. In the mixing mode the high-frequency oscillations of the received signal are fed to the first control grid from the cathode, and high-frequency oscillations from a separate auxiliary oscillator (the heterodyne oscillator) are fed to the third control grid from the cathode. In the conversion mode the signal is fed to the third grid, and the first grid, together with the cathode, forms an auxiliary oscillator.