Abstract :
The anode-current/grid-voltage characteristics of valves are determined with the help of diagrams and design charts based on Langmuir´s data on the current flow in plane diodes with consideration of initial electron velocities, and on Oertel´s and Herne´s equations for the amplification factor. The theory is extended to multi-grid valves and to valves possessing a more complicated shape. Special attention is given to the ¿variable-mu effect,¿ which represents one of the limiting factors in practical valve construction. A simple expression describing this effcct is derived, and a chart of the ¿variable-mu constant,¿ ¿, is presented, in which space charge is taken into account. Measurements on specially made experimental valves and on several types of modern mass-produced valves confirm the treatment of the variable-mu effect and show that the methods outlined in the paper, forming a complete design system, allow the prediction of the static valve characteristic with good accuracy even in closely spaced modern valves. Finally, the influences of a change in control-grid wire diameter, of a statistical variation of control-grid pitch, and of cathode misalignment, are discussed.
