GAS-FILLED DISCHARGE TUBE

A gas-filled discharge tube for voltage control particularly for the series gap of the ignition system of an automotive spark-ignition engine. The gas-filled discharge tube is capable of operating stably at a sufficiently high discharge inception voltage, requires a sufficiently low discharge sustaining voltage and is capable of accurately controlling the ignition timing of the automotive spark-ignition engine regardless of the variation of the output voltage of the ignition coil of the ignition system. The gas-filled discharge tube is provided with discharge electrodes meeting requirements that the opposite surfaces of the discharge electrodes are substantially flat, the discharge electrodes have no sharp edge, and the product of the diameter of the discharge electrodes and the distance between the discharge electrode is 20 mm2 or below. The gas-filled discharge tube is filled with a mixed gas having a composition of 50% by volume or below in nitrogen content and 50% or above in argon content.