Two voltage regulators are described. The first is satisfactory where there is only a very small current drain; the second will maintain constant voltage output up to the current carrying capacity of the radio tube. For each the change of output voltage with change of input can be made zero. Where extreme constancy is required, the second circuit described is recommended. It approximates closely perfect regulation. The coefficient of voltage change of the output, defined by (1/V0)(∂V0/∂Vi) whereV0is the output voltage andViis the input voltage, is less than 10−7per volt. The regulation is equally as good for surges as for longer random or periodic fluctuations. The circuit also maintains a constant voltage output for varying current drains, the output resistance being about 10 ohms. Currents up to 100 milliamperes at several thousand volts may be drawn with no significant change in the output voltage. The coefficient of drift defined by (1/V0)(∂V0/∂t), wheretis the time, will usually be less than 10−4per hour even under normal laboratory conditions where no special precautions are taken.