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FunctionThis is one of the earliest amplifier vacuum tubes or triodes by Lee De Forest. It consists of a cathode of thin filaments, a plate that acts as an anode, and a curved wire between them that was called the grid. For some time it remained unclear how exactly the device worked, but the fact was that it enhanced the detection of radio signals. It was shown later that it worked by amplifying the radio signal detected by the circuit: If one connects the cathode and anode to a voltage source, a current is established, maintained by the electrons produced at the cathode that fly towards the anode. When one connects the grid to a negative voltage, it will prevent some of the electrons from reaching the anode, thereby reducing the current. That way one can modify the current by small changes in the grid voltage. If the grid is attached to an antenna, the effect is to amplify the small signal it receives.