An attempt has been made to derive, in terms of valve geometry, theoretical expressions for the constants of an elliptic triode, the shape of the electrodes of which belongs to a family of confocal ellipses. The amplification factor (μ) is derived by following the method of conformal transformation. Result shows that in general it varies with the parametric angle θ of the ellipse—decreasing from the direction of minor to that of the major axis. The average value of μ increases with increasing value of the eccentricity of the grid and with decreasing value of the eccentricity of the anode. Curves for ready evaluation of μ for any value of θ are given. The problem of design of an elliptic triode having a constant μ for all values of θ is also considered and its method of solution indicated. An expression for the perveance (P) has also been obtained by adopting the procedure followed by O'Neill for determining the perveance of a plane diode having filamentary cathode. The expression shows that the value of perveance is determined mainly by the eccentricity of the grid and the focal distance. To illustrate the practical applications of the various deductions made, a numerical example, involving the design of a 6C5‐GT/G type triode, is given.