Editing Cathode-ray tube (section)

===Monochrome CRTs===
[[File:Mini Star 416 - cathode ray tube with deflection coils-2210.jpg|thumb|180px|An aluminized monochrome CRT. The black matte coating is aquadag.]]
[[File:Mini Star 416 - cathode ray tube, deflection coils-2146.jpg|thumb|180px|The deflection yoke over the neck of a monochrome CRT. It has two pairs of deflection coils.]]
If the CRT is in black and white (B&W or monochrome), there is a single electron gun in the neck and the funnel is [[aluminized screen|coated on the inside with aluminum]] that has been applied by evaporation; the aluminum is evaporated in a vacuum and allowed to condense on the inside of the CRT.<ref name="auto52"/> Aluminum eliminates the need for [[ion trap]]s, necessary to prevent ion burn on the phosphor, while also reflecting light generated by the phosphor towards the screen, managing heat and absorbing electrons providing a return path for them; previously funnels were coated on the inside with aquadag, used because it can be applied like paint;<ref name="auto29"/> the phosphors were left uncoated.<ref name="auto68"/> Aluminum started being applied to CRTs in the 1950s, coating the inside of the CRT including the phosphors, which also increased image brightness since the aluminum reflected light (that would otherwise be lost inside the CRT) towards the outside of the CRT.<ref name="auto68"/><ref>{{Cite web|url=https://patents.google.com/patent/US2819182A/en|title=Process of aluminizing cathode ray tube screen}}</ref><ref>{{cite journal |last1=Bowie |first1=R.M. |title=The Negative-Ion Blemish in a Cathode-Ray Tube and Its Elimination |journal=Proceedings of the IRE |date=December 1948 |volume=36 |issue=12 |pages=1482–1486 |doi=10.1109/JRPROC.1948.232950 |s2cid=51635920 }}</ref><ref>{{cite journal |last1=Dudding |first1=R.W. |title=Aluminium backed screens for cathode ray tubes |journal=Journal of the British Institution of Radio Engineers |volume=11 |issue=10 |year=1951 |pages=455–462 |doi=10.1049/jbire.1951.0057 }}</ref> In aluminized monochrome CRTs, Aquadag is used on the outside. There is a single aluminum coating covering the funnel and the screen.<ref name="auto52"/>

The screen, funnel and neck are fused together into a single envelope, possibly using lead enamel seals, a hole is made in the funnel onto which the anode cap is installed and the phosphor, aquadag and aluminum are applied afterwards.<ref name="auto37"/> Previously monochrome CRTs used ion traps that required magnets; the magnet was used to deflect the electrons away from the more difficult to deflect ions, letting the electrons through while letting the ions collide into a sheet of metal inside the electron gun.<ref>{{Cite magazine|title=Cathode-ray Tubes 1 <!--https://worldradiohistory.com/hd2/IDX-UK/Technology/Technology-All-Eras/Archive-Practical-Television-IDX/50s/Practical-Television-1959-01-OCR-Page-0029.pdf-->|date=January 1959|magazine=Practical Television}}</ref><ref name="auto53"/><ref name="auto28"/> Ion burn results in premature wear of the phosphor. Since ions are harder to deflect than electrons, ion burn leaves a black dot in the center of the screen.<ref name="auto53"/><ref name="auto28"/>

The interior aquadag or aluminum coating was the anode and served to accelerate the electrons towards the screen, collect them after hitting the screen while serving as a capacitor together with the outer aquadag coating. The screen has a single uniform phosphor coating and no shadow mask, technically having no resolution limit.<ref>{{Cite web|url=http://www.thg.ru/display/20011128/print.html|title=CRT Guide - A THG Primer - THG.RU|date=July 22, 2017|website=www.thg.ru}}</ref><ref name="auto79"/><ref name="auto91">{{cite web |url=https://www.earlytelevision.org/pdf/manufacture_of_color_pic_tubes.pdf |archive-url=https://web.archive.org/web/20150905122030/http://www.earlytelevision.org/pdf/manufacture_of_color_pic_tubes.pdf |archive-date=2015-09-05 |url-status=live |title=Manufacture of color picture tubes|website=www.earlytelevision.org |access-date=2020-12-11}}</ref>

Monochrome CRTs may use ring magnets to adjust the centering of the electron beam and magnets around the deflection yoke to adjust the geometry of the image.<ref name="auto19"/><ref>{{Cite web|url=https://www.repairfaq.org/REPAIR/F_monfaq4.html#MONFAQ_010|title=Sci.Electronics.Repair FAQ: Notes on the Troubleshooting and Repair of Computer and Video Monitors|website=www.repairfaq.org}}</ref>

When a monochrome CRT is shut off, the screen itself retracts to a small, white dot in the center, along with the phosphors shutting down, shot by the electron gun; it sometimes takes a while for it to go away.<ref>{{Cite web |last=Y |first=Roshni |date=2019-10-14 |title=What is Monochrome Picture Tube? Construction and Working of Monochrome Picture Tube |url=https://electronicsdesk.com/monochrome-picture-tube.html |access-date=2024-12-12 |website=Electronics Desk |language=en-US}}</ref>

<gallery mode="packed" heights="110px">
File:Osziroehre.jpg|Older monochrome CRT<ref>[http://www.earlytelevision.org/postwar_crts.html Early television] [https://www.crtsite.com/tv-crt.html The Cathode Ray Tube site] [http://www.earlytelevision.org/14ap4_construction.html Picture Tubes]</ref> without aluminum, only aquadag
File:Monochrome CRT electron gun close up.jpg|The electron gun of a monochrome CRT
</gallery>