They are also somewhat resistant to cathode poisoning.

This process is known as cathode poisoning.

Valves have a shorter working life than solid state parts due to various failure mechanisms (such as heat, cathode poisoning, breakage, or internal short-circuits).

Some sources suggest that incomplete glow coverage of a glyph ("cathode poisoning") or appearance of glow elsewhere in the tube would not be acceptable.

This is due various commonplace failure mechanisms: cathode depletion, open or shorts circuits-notably of the heater and grid structures, cathode poisoning, and physical breakage of the glass envelope.

The special quality could be anything, from rugged designs for military and industrial use, through devices with exceptionally low noise and microphony, to designs primarily optimised for long life without cathode poisoning when used for switching in a digital computer (but not necessarily with exceptional qualities as an amplifier).