Assertion: heated cathode | /r/ObjectUse | used in first vacuum tubes
Facets:
Source sentences:
text: Directly heated cathodes were used in the first vacuum tubes, but today they are only used in fluorescent tubes, some large transmitting vacuum tubes, and all X-ray tubes.
text: Directly heated cathodes were used in the first vacuum tubes, but today they are only used in fluorescent tubes, some large transmitting vacuum tubes, and all X-ray tubes.
text: Directly heated cathodes were used in the first vacuum tubes.