The GA4 is a large spark gap T/R cell tube of unknown specification, which was used in the SCR-270 'Pearl Harbor' radar system. The two electrode contacts on either side of the envelope are designed to be removed, and are held in place by a pair of Allen screws. The inner electrodes are made of tungsten, and had a tendency to become fouled with sputtered material after prolonged use. For this reason the GA-4 contains a small amount of powdered tungsten, and it was recommended that the tube be periodically shaken vigorously to scrub the inside free of fouling. This tube illuminates purple when subjected to an electrostatic field, which suggests it is filled with either hydrogen or water vapor.
Later versions of the SCR-270 radar system phased out the use of GA-4 TR cells in favor of the Westinghouse 1B32 spark gap tube.
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