Would you be able to reseal the cracked glass and regenerate the vacuum through the other end?

More glass, epoxy, or similar?

Plastic generally isn't an air tight seal. The leaks may be slow, but generally we hope vacuum tubes last for years.

	▲	Supernaut an hour ago \| parent [-]
		> generally we hope vacuum tubes last for years If I may offer an anecdote, the output stage in my guitar amplifier is powered by a GEC tube that is now 55 years old. It sounds great. When I found the tube, it had been rolling around for a couple of decades at the bottom of a wooden box. This could simply be survivorship bias, but it does appear that back in the day, they knew how to build these things to last.

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adrian_b 5 hours ago | parent | prev [-]

An accidental crack can be resealed, but if the crack had appeared because inappropriate materials were used, e.g. an unsuitable metal-glass pair, resealing is pointless, because cracks will appear again after the device is turned on and off several times, causing expansion-contraction cycles.