Late to the party, and maybe bringing it back nearer where it started.
I'm interested in electronic calculators between 1960 and 1975 and have restored many to working condition. Transistors, early generation ICs, linear power supplies. See
dopecc.net if you are interested.
These machines are generally over fifty years old, were expensive in their day and could use best quality parts, but some of these were of course bleeding edge tech. To the original question - I am generally impressed at the longevity of these machines over a 50 year period.
Some general observations:
- transistors age well, failures seem random and uncommon, I have not found a plague of tin whiskers (yet)
- early DTL and TTL ICs have aged well. I typically find plastic packages and these are surely not hermetic. eg plastic Fairchild 99xx DTL chips from 1960s aged badly in a machine stored many years in a barn, but interestingly the plastic TI parts in same machine did well.
- old electrolytics are most often OK, but I recognise some types of Sprague from 1960s that are often dried out. But my experience is that wholesale recapping is not indicated
- likewise old tantalums, mostly OK but a small proportion do go short. I fix if/as they fail and leave the rest
- mechanical connections are one of the largest failure groups, mostly oxidized/corroded connectors. Wire wrap seems to live up to its reputation for longevity (if done to standard in first place)
- and remember that these are mostly digital circuits, so tend to be tolerant of maybe up to 30% drift in value of composition resistors and ceramic caps. If I were playing with vintage radio, these effects may be more significant
So my experience is that over a 50-year time frame, if in reasonable conditions of temp and humidity, the semiconductors and components generally seem to age very well.
Also maybe of interest are the early computers I have. These may have UVEPROMS and my experience in machines from the 80s is that the data survives after 40 years, far longer than the original specifications suggested.
Small and specific samples I know, but maybe interesting observations from actual vintage machines.