Power grid tubes

Abstract

Even though their use has declined considerably, studying the properties of vacuum diodes is important for a better understanding of the principles of operation of power grid tubes. A vacuum diode consists of two electrodes in a vacuum: a thermoelectronic cathode and an anode. When the cathode temperature is high enough, it can emit electrons from the surface. The anode is brought to a positive voltage V _p with respect to the cathode, and thus attracts electrons emitted by the cathode, giving rise to a current I _p between the cathode and anode. The curve I _p versus V _p is called the diode characteristic. For a given cathode temperature T, I _p increases with V _p up to a maximum current I _m. For a higher cathode temperature T′ > T, the characteristic curve is the same up to I _m, but continues to increase to a higher maximum current I _m′ > I _m (Fig. 3.1).