1966 · Vacuum Fluorescent Display · Work 927 of 1,871
A small experimental workshop in a coastal town in Japan on an evening in early spring, on a worn wooden bench a slender blue gas flame and a pump of glass tubing and brass, in a small socket a single upright glass tube three centimetres tall with a sealed tip and a ring of thin wire legs, inside it on a dark grey plate behind a fine mesh two short bars and a dot glowing soft blue-green, a hand holding with fine tweezers a second, still open tube with a white ceramic plate, a few spare tubes on a folded cloth, sliding windows with paper panes in warm evening light.
What it was used for
The Digitron tube made by Ise Electronics was a display component for calculating machines. The Nikkan Kogyo Shimbun reported on 25 January 1968 that Hayakawa Electric Industry had taken part in its development and was one of the first to adopt it for its Compet 16 desk calculator; the article names Japanese calculator makers seeking an alternative to neon numeric display tubes, whose manufacture and driving touched US patents held by Burroughs, as the source of demand. Documented in a machine is the Itron brand in the Sharp QT-8D of December 1969, 8 digits, $395. The Casio Mini, sold from August 1972 for 12,800 yen, had 6 vacuum fluorescent display tubes.
What was new
The difference from the Nixie tube lay in voltage and in depth: the IEEE milestone proposal gives about 25 V driving voltage for the production DG12B tube against about 170 to 200 V for Nixie tubes, in which the digits also sat at different depths. The 1968 article gives the same reasons: all digits at the same depth and therefore easier to read, green light, about 800 lux at low voltage. Patent US 3,508,101 claims in claim 1 an evacuated envelope with a heated cathode, a fluorescent-coated anode and an accelerating grid, and in claim 2 the segmented anode. Who invented the tube is answered three different ways: the IEEE plaque names Tadashi Nakamura as the man who commercialized it in 1967, the SID's Karl Ferdinand Braun Prize went in 1991 to Kentaro Kiyozumi and Nakamura "For the invention of the vacuum fluorescent display", and the inventor named in the patent is Mikiharu Tanji.
What the sources leave open: Noritake answers the year two different ways on one page: 1967 as the invention in the running text, 1966 in the timeline for the basic structure and 1967 for the single-digit tube. The first installation is not free of contradiction: the IEEE proposal and the Japanese press name Sharp's CS-16A, whereas Rick Bensene describes his own example as a Nixie machine with tubes by NEC. The IPSJ does not say who supplied the Casio Mini's tubes; no source gives a life in hours.