A vacuum tube is based on current conduction through a vacuum (see Vacuum tube).
Diode or rectifier tube
Amplifying tubes
Triode
Tetrode
Pentode
Hexode
Pentagrid
Octode
Microwave tubes
Klystron
Magnetron
Traveling-wave tube
Optical detectors or emitters
Phototube or Photodiode – tube equivalent of semiconductor photodiode
Photomultiplier tube – Phototube with internal gain
Cathode ray tube (CRT) or television picture tube
Vacuum fluorescent display (VFD) – Modern non-raster sort of small CRT display
Magic eye tube – Small CRT display used as a tuning meter (obsolete)
X-ray tube – Produces x-rays