It is suggested that the rating of small-and medium-power thermionic rectifier valves in capacitance-input circuits requires amending, so that the full-load conditions may be deduced from the basic properties of the valves in a more general manner, and the usual family of regulation curves, supplied to show the performance at loads less than maximum, may be replaced by curves more suited to the design of rectifying equipment.It is further suggested that these improvements may be obtained by including, as part of the rating, recommended values for two parameters, namely the ratio of the source to the load resistance (R5/R0), and the product of the load resistance and the admittance of the input condenser (ωCR0)This parameter specification controls the circuit conditions under which the valves are operated and ensures that, independent of the type of valve, full-load operation is always accompanied by a particular set of waveforms. The ratios, such as peak/mean value, etc., that characterize these waveforms have been measured and are compiled into a Table which permits the full-load performance of a valve to be evaluated from its basic properties. In addition, an investigation has been made upon the parameter values in equipments employing valves at less than their maximum output. This investigation has led to the preparation of fractional-load performance curves, on which every point gives the full-load performance of an equipment designed to make the best use of the valve at the particular fraction of its maximum output.