The Z550 is a pixie tube with a twist, it is a display that includes its own switching thyratrons for easy control from a 5 volt TTL signal. Each digit contains a small starter electrode that pierces a ring anode and cathode plates to poke into the cavity behind the digit stamp. By controlling the voltages present on the anode and cathode, it is possible to put the tube in a state where a mere five volt pulse on the starter electrode will trigger the glow discharge for the selected digit. The entire display assembly is constructed on a thick glass billet which is then sealed in the tube's 13 pin envelope; unlike the Burroughs HB-105 and 9012, the Z550 envelope is relatively devoid of empty space. As with the Burroughs pixie tubes discussed above, the 5 volt control scheme is almost never used by modern experimenters, who typically use a traditional Nixie control system connected to the tube's starter electrodes instead.
It should be noted that all Z550 tubes were made by Phillips in their Eindhoven plant, regardless of the manufacturer's stamp. Z550 tubes were restamped near the time of sale to match the nameplate for the target country.
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