by kragen | 2025-08-24 01:37:35+00:00
Gas-discharge tubes are kind of niche today, and vacuum tubes have been more important since at least the 01920s, but in the 01960s, gas tubes weren't that niche; people used them for signal switching, voltage regulation, light detection, breakover elements for relaxation oscillators, digital displays https://en.wikipedia.org/wiki/Nixie_tube, counters https://en.wikipedia.org/wiki/Dekatron, and other memory devices. https://en.wikipedia.org/wiki/Neon_lamp#Applications has a bit of a catalog of uses, which references this actual catalog of devices from 01966 https://archive.org/details/ge-glow-lamp-manual-1966/page/n1... and Miller's 01969 book https://www.tiffe.de/roehren/neon.pdf. Geiger tubes are still used for detecting ionizing radiation, although we have other alternatives today. And of course most forms of electrical lighting have been gas discharge lamps since Davy invented the first commercial electric light around 01809: the open-air arc lamp, the neon lamp or tube, the fluorescent tube, the mercury light, low-pressure and high-pressure sodium-vapor lamps, strobe lights, and continuous high-intensity discharge xenon lamps.

The 01951 book I learned digital logic from, by Dennis Ritchie's father and two of his Bell Labs colleagues, has a chapter on switching with "electron tubes, both vacuum and gas-filled," and "semi-conductors": https://archive.org/details/TheDesignOfSwitchingCircuits/pag....

(Fluorescent light bulbs, by the way, do have a heated filament, and do work by thermionic emission, though cold-cathode fluorescents like those used in old LCDs don't.)

The respective niches of vacuum tubes and gas switching tubes could be very crudely summarized as high speed and high reliability. Even primitive vacuum tubes had switching times in the microseconds, and by WWII it was below a nanosecond, like transistors, but they relied on hot filaments that eventually burned out. Cold-cathode gas tubes, by contrast, essentially never break, but they take close to a millisecond for the gas to deionize so they can stop conducting. They can switch higher-frequency signals, but they can't switch on and off faster than that. Keister, Ritchie, and Washburn say of hot-cathode gas tubes:

> The speed of response of the tube is contingent primarily on the ionization and de-ionization times of the tube. Depending upon the gas, the ionization time ranges from a fraction of a microsecond to several microseconds; the de-ionization time is ordinarily of the order of a hundred to a thousand microseconds, though lower values have been achieved. The tube, then, can respond very rapidly to input signals applied to operate the tube, but considerably more time must be allowed for extinguishing the tube.

When I first read this when I was eight, "a hundred to a thousand microseconds" presumably sounded incredibly fast, but of course it's painfully slow for computation. Of cold-cathode tubes, they say:

> Moreover, since the cold-cathode tube has no filament, no standby current is consumed. The speed of response, though somewhat less than that of the hot-cathode gas tube, is sufficient for most applications. The ionization time depends upon the time necessary to transfer the discharge from the starter gap to the main gap, and it is generally less than a hundred microseconds. Main gap de-ionization times are of the order of one to ten milliseconds.

You might hope that this would have improved since 01951, but, as far as I can tell, it never did.

They continue:

> Because of its suitability to switching circuits, the electron tube circuit examples contained in the remainder of the chapter are, in the majority of cases, based on the cold cathode-tube.

(They do, however, include a few vacuum-tube circuits.)

The rest of the book is about relays. Vacuum tubes and semi-conductors were, from their point of view, niche.