One control grid carried the incoming RF signal, while the other was connected into an oscillator circuit which generated the local oscillation within the same valve. Since the anode current of the bi-grid valve was proportional both to the signal on the first grid, and also to the oscillator voltage on the second grid, the required multiplication of the two signals was achieved, and the intermediate frequency signal appeared in an appropriately tuned circuit connected to the anode. In all of the applications mentioned, the bi-grid tetrode acted as an analogue multiplier (analog multiplier) which multiplied together the signals applied to the two grids.