rectifying valve vs vacuum tube

rectifying valve and vacuum tube both are nouns.

Word	Noun	Adjective	Verb	Adverb
rectifying valve	Yes	No	No	No
vacuum tube	Yes	No	No	No

As nouns, vacuum tube is a hypernym of rectifying valve; that is, vacuum tube is a word with a broader meaning than rectifying valve:

rectifying valve: a thermionic tube having two electrodes; used as a rectifier
vacuum tube: electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope

Other hypernyms of rectifying valve include electron tube, thermionic tube, thermionic vacuum tube, thermionic valve, tube.

rectifying valve (noun)	vacuum tube (noun)
a thermionic tube having two electrodes; used as a rectifier	electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope