I would say your grandpa was a true broadcast/electronics enthusiast.
Lots of the less enthusiastic technology lovers still only had radios at that point.
Regardless of the electronics or the decade that spawned it, the unfortunate terminal behavior of that TV set was characteristic of what is known in electronic assembly as a "birth defect".
Quite possibly a single marginal key component or miswiring mistake, and from your account most likely not a vacuum tube itself and very much more unlikely the entire set of original tubes or replacements.
I wouldn't rule out a bad socket though.
Seems to have gone down in history as one of the most ridiculously premature failures people would always remember.
Anyway it did seem to perform normally for a short while before it just up and died, both times, and I think that modern electronics having an equivalent assembly goof-up probably would not even make it once.
So that may speak a bit about a preference for overly-robust engineered electronics that could be lost for decades now.
Entirely unfulfilled with this fateful TV, I know the feeling well but I think it has gotten much worse in the 21st century.
Even if only one tube socket was the cause of the failure, those sockets were what made it much more possible from the beginning for users to keep their own electronics running if they were so inclined, simply taking their own tubes to Radio Shack for testing at a minimum could accomplish a lot.
Not everyone would do this back then but it would be kind of equivalent to those who would rather not add extra memory to their PCs themselves. Neither one should you be doing willy-nilly. More of an upgrade here than a repair but you're still putting components in sockets.
Well a good bit of user repairability was once assumed because there was not any ingrained kind of disposable society, and the devastatingly senseless losses and massive-scale waste of World War II had still not dampened the spirit of Americans for things that last.
Then in the 21st century when digital TV broadcasts took over from analog using the same proven radio frequencies, power levels, and antennae, this was the first time a higher resolution picture was possible since way back when analog TV was standardized by NTSC. The picture's capable of being as perfect as cable when you have an interference-free signal, but that's a certain additional requirement for near-perfection that was however not met often enough.
Seems engineers "forgot" that analog TV was based on radio and the further you got from the broadcast station the worse your picture got until there was nothing but audio for a number of additional miles away from the antenna.
With digital you lost it all, abruptly, beyond a much smaller range.
Ever since.
And TV channels take a lot longer to change, the difference between zero latency and some latency is most uncanny. Like many things defying the type of expectations people had for progress after 1955, that were futuristically anticipated to be realized during the 21st century.