Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Vacuum Tube. Gas-Filled Tube, Irving Langmuir, Magic Eye Tube, Mullard-Philips Tube Designation, Nixie Tube, RETMA Tube Designation, RMA Tube Designation, Tube Sound, Tube Tester, Vacuum Fluorescent Display, Valve Amplifier, Vacuum, Thermionic Emission, Cathode Ray Tube, Incandescent Light Bulb, Tube Socket, Crookes Cube, Geissler Tube, Eugen Goldstein, Johann Wilhelm Hittorf, Nikola Tesla, Pentagrid Converter, 12AX7, X-ray Tube, Traveling-Wave Tube, Article Sources and Contributors, Image Sources, Licenses and Contributors