Random objects: the nuvistor

The transistor changed the world — but it happened so quickly because we knew precisely what needed to be done. The fundamental circuits for communications and computing have been developed in the era of vacuum tubes; and as luck would have it, the transistor behaved much like a vacuum tube.

Of course, on a physical level, the two devices are nothing alike. Vacuum tubes work by the principle of thermionic emission — a phenomenon that allows electrons escape into vacuum from an electrode that is heated to a glow. The simplest vacuum tube has a heated cathode and a room-temperature anode, letting the current flow in one direction and forming a simple rectifier. A more exciting variant — a triode — adds a metal grid in between. A negative voltage applied to the grid repels electrons and moderates the flow of current between the other two terminals.

Interestingly, vacuum tubes went extinct despite being electronically superior; they offered better linearity and switching characteristics than any transistor back in the day. Practicality prevailed: it sufficed that the transistor had a greatly reduced power footprint thanks to not needing a heating coil.

At this point, some readers might object: surely, the transistor was also a more compact and more rugged device! Well… yes, but also no. Meet the nuvistor:

Nuvistor model 7586, assembled and removed from can. Photo by author.

Developed by the RCA corporation in 1959, this subminiature vacuum tube had a form factor similar to the early transistors. It ditched the traditional glass enclosure for a metal can with a ceramic base. Removing the can revealed a complex internal structure with three electrodes and a heater sandwiched inside a tubular structure:

Microscope photo of a nuvistor with can removed, by author.

Nuvistor design schematics from the RCA catalog.

Who knows — perhaps, had we discovered solid-state semiconductors a bit later or fusion power a bit earlier, our electronics would have been controlled by vacuum tube ICs.