Editing Cathode-ray tube (section)

===Cat's eye===
{{Main|Magic eye tube}}
In some [[vacuum tube]] radio sets, a [[Magic eye tube|"Magic Eye" or "Tuning Eye" tube]] was provided to assist in tuning the receiver. Tuning would be adjusted until the width of a radial shadow was minimized. This was used instead of a more expensive electromechanical meter, which later came to be used on higher-end tuners when transistor sets lacked the high voltage required to drive the device.<ref>{{cite web |url=http://www.vacuumtube.com/eyetubes.htm |title=Tuning-Eye Tubes |access-date=1 December 2009 |publisher=vacuumtube.com |url-status=dead |archive-url=https://web.archive.org/web/20090423055711/http://www.vacuumtube.com/eyetubes.htm |archive-date=23 April 2009}}</ref> The same type of device was used with tape recorders as a recording level meter, and for various other applications including electrical test equipment.