Tubes have a limited lifetime, but high-reliability, long-life tubes were developed specifically for digital circuits.
One such development was a change in alloys for the filaments. It turns out that the filaments were made from a tungsten alloy containing silicon, and the silicon evaporates and is deposited on the cathode. The cathode has a special coating to help it emit electrons, and the silicon deposits would interfere. From what I can tell, the alloy for filaments had silicon in to make it easier to draw through the dies necessary to construct the filament in the first place, so there is some tradeoff between the lifetime of the tools used to make the tubes and the lifetime of the tubes themselves.
This is not entirely unlike the problems faced by semiconductor manufacturers—problems with impurities, solid state chemistry, and vapor deposition. I can imagine an alternate timeline with extremely long-lived vacuum tube circuits.
I recently read up on "zone melting" which was developed to purify germanium - but of course this same method can be used for other materials. Interesting that Hamming of Hamming codes fame gave encouragement to the developer of this materials process: https://fs.blog/great-talks/richard-hamming-your-research/ (search for Bill Pfann)
One such development was a change in alloys for the filaments. It turns out that the filaments were made from a tungsten alloy containing silicon, and the silicon evaporates and is deposited on the cathode. The cathode has a special coating to help it emit electrons, and the silicon deposits would interfere. From what I can tell, the alloy for filaments had silicon in to make it easier to draw through the dies necessary to construct the filament in the first place, so there is some tradeoff between the lifetime of the tools used to make the tubes and the lifetime of the tubes themselves.
This is not entirely unlike the problems faced by semiconductor manufacturers—problems with impurities, solid state chemistry, and vapor deposition. I can imagine an alternate timeline with extremely long-lived vacuum tube circuits.