Abstract: An apparatus for regulating the temperature of a model engine glow plug filament. Between pulses from a power circuit, an amplifier applies its output voltage to a filament current path comprising the filament and a resistive circuit. By means of feedback to the amplifier, the filament voltage is kept at a predetermined reference, and the output voltage is thereby an indication of the filament resistance, which is related to its temperature. The output voltage charges a capacitor whose discharge time determines the "on" time of the power pulses. By this method, temperature is regulated, and power is totally cut off when the filament temperature gets sufficiently high.