Space-Charge Grid Tube

an electron tube containing an additional grid (cathode grid) between the cathode and the control grid. The use of such a grid in radio receiving tubes (triodes and pentodes) increases the slope of their characteristic up to several tens of milliamperes per volt (mA/V) or makes possible preservation of their basic parameters at reduced electrode voltages (12-24 V).

Space-charge grid tubes with input and output capacitances somewhat lower than those of conventional triodes and pentodes were produced as a result of rational electrode design; this together with a steeper slope of the characteristic curve increases the efficiency of use of such tubes in television, radar, and other similar amplifiers with a broad pass band. Among the disadvantages of space-charge grid tubes are the use of a separate power supply for the cathode grid that has a low positive voltage (10^-15 V) but a comparatively high current (dozens of milliamperes), and also an increased noise level.