contactors would be required when switching from the inventive system to the kettering system or vice versa such readjustment of dwell angle is avoided by utilizing the additional stage q1 such switch q1 changes the timing and dwell logic compatible to a kettering system to enable convenient switching therebetween a unipolar alternating current rectangular wave generator 30 is duty cycled by the timer so that such generator is quiescent during the period when primary winding 61 is being charged and is conductive during discharge periods of winding 61 unipolarity of the ac output wave is obtained by virtue of one one end of winding 32 being at ground or reference potential such generator is connected to the collector of qn and modulates the discharge current from winding 61 during the discharge mode of the system providing a plural number of pulses in the resultant modulation envelope which effectively increases the energy level fed to any igniter it should be emphasized that although a rectangular wave generator was used in view of its convenience in construction and simplicity of configuration that any ac generator providing any waveform or even random waves may be used as a modulation source this system does not depend upon a capacitor to create an ignition oscillation inasmuch as this system will function as shown without generator 30 being connected thereto providing ignition power as.