[MrBuddyCasino]

Why would a vacuum tube „pop“ when exposed to vacuum?

[analog31]

Possibly nowhere for the heat to go. Some tubes need a certain amount of ventilation depending on the application. It wouldn't pop, but might fail.

[numpad0]

Some of Soviet spacecrafts were known to have been built around ~1atm pressure vessels as a brute force means to reduce unknown unknowns. I suspect it could be reverse reasoning from there.

[dmix]

probably because the vacuum of space is way more extreme than inside the tube which would cause pressure on the seals

[teraflop]

Vacuum tubes typically have an internal pressure of less than 0.001 atm, sometimes much less.

Any seal that can withstand a pressure difference of 0.001 atm to 1 atm from the outside can almost certainly withstand a difference of 0.001 atm to 0 atm from the inside.