Factors Influencing the Perveance of Power-Output Triodes

A brief historical survey, discussing Child's formula and the assumptions upon which it was derived, is presented. Perveance is explained as being the factor relating voltage to current in electron tubes, and several formulas for calculating it are listed. The concept of "equivalent diodes" is discussed. Formulas are given for computing cathode current, together with reasons for errors in these formulas. Brief explanations are offered of the effects of grid current, variations in "effective anode area," and variations in μ upon calculations of cathode current.