Radio parts are essential components of a radio. Diodes (6 letters) are semiconductor devices that allow current to flow in one direction, and are used to control the current in a circuit. DIALS (5 letters) are used to adjust the frequency of a radio signal. Tuners (6 letters) are electronic circuits that select a specific frequency from a range of frequencies. TUBES (5 letters) are vacuum-sealed glass containers filled with electrodes, and are used to amplify signals in a radio.