Editing Cathode-ray tube (section)

==Constructions==
===Body===
[[File:Coating CRTs at Research Enterprises.jpg|thumb|Small circular CRTs during manufacturing in 1947 (screens being coated with phosphor)]]
[[File:Mini Star 416-8834.jpg|thumb|A portable monochrome CRT TV]]
[[File:Trinitron computer-monitor.jpg|thumb|A [[Trinitron]] CRT computer monitor]]
[[File:Mini Star 416 - cathode ray tube-2140.jpg|thumb|A monochrome CRT as seen inside a TV. The CRT is the single largest component in a CRT TV.]]
[[File:Macintosh Plus interior.jpg|thumb|A monochrome CRT as seen inside a [[Macintosh Plus]] computer]]
The body of a CRT is usually made up of three parts: A screen/faceplate/panel, a cone/funnel, and a neck.<ref>{{Cite patent |country=EP |number=0088122B1 |url=https://patents.google.com/patent/EP0088122B1/en |title=Large metal cone cathode ray tubes, and envelopes therefor}} calls it faceplate {{Cite patent |country=US |number=20040032200A1 |url=https://patents.google.com/patent/US20040032200A1/en|title=CRT having a contrast enhancing exterior coating and method of manufacturing the same}} also calls it faceplate {{Cite patent |country=US |number=20060132019A1 |url=https://patents.google.com/patent/US20060132019A1/en|title=Funnel for use in a cathode ray tube}}</ref><ref>{{cite web |url=https://www.illinoisrecycles.org/wp-content/uploads/2014/10/150618_T_3.1_ChrisCahnovsky.pdf |archive-url=https://web.archive.org/web/20210228121122/https://www.illinoisrecycles.org/wp-content/uploads/2014/10/150618_T_3.1_ChrisCahnovsky.pdf |archive-date=2021-02-28 |url-status=live |title= Case study|last= Cahnovsky|first=Chris |website=www.illinoisrecycles.org |access-date=2020-12-11}}</ref><ref name="auto34">{{cite journal |last1=Ha |first1=Kuedong |last2=Shin |first2=Soon-Cheol |last3=Kim |first3=Do-Nyun |last4=Lee |first4=Kue-Hong |last5=Kim |first5=Jeong-Hoon |title=Development of a 32-in. slim CRT with 125° deflection |journal=Journal of the Society for Information Display |date=2006 |volume=14 |issue=1 |pages=65 |doi=10.1889/1.2166838 |s2cid=62697886 }}</ref><ref name="auto104">{{cite web |url=https://dnr.mo.gov/env/hwp/escrap/docs/crttcp99.pdf |title=Characterization of Lead Leachability From Cathode Ray Tubes Using the Toxicity Characteristic Leaching Procedure |date=1999 |website=dnr.mo.gov |access-date=2020-12-11 |archive-date=6 March 2021 |archive-url=https://web.archive.org/web/20210306075506/https://dnr.mo.gov/env/hwp/escrap/docs/crttcp99.pdf |url-status=dead }}</ref><ref name="auto73">{{Cite web|url=https://www.vice.com/en/article/americas-television-graveyards/|title=America's Television Graveyards|website=Vice.com|date=16 February 2017 }}</ref> The joined screen, funnel and neck are known as the bulb or envelope.<ref name="auto42"/>

The neck is made from a glass tube<ref>{{Cite patent |country=CN |number=1545118A |url=https://patents.google.com/patent/CN1545118A/en |title=Processing technique for straight tube necking glass cone for CRT}}</ref> while the funnel and screen are made by pouring and then pressing glass into a mold.<ref>{{Cite patent |country=US |number=3484225A |url=https://patents.google.com/patent/US3484225A/en|title=Method of reforming glass face plates on a shaping mold}}</ref><ref>{{Cite patent |country=US |number=7093732B1 |url=https://patents.google.com/patent/US7093732B1/en|title=CRT funnel with positioning reference portions}}</ref><ref>{{Cite patent |country=US |number=20060001351A1 |url=https://patents.google.com/patent/US20060001351A1/en|title=Glass panel and a cathode ray tube including the same}}</ref><ref>{{Cite patent |country=US |number=3264080A |url=https://patents.google.com/patent/US3264080A/en|title=Method for forming rectangular face plate}}</ref><ref>{{Cite patent |country=JP |number=3539635B2 |url=https://patents.google.com/patent/JP3539635B2/en |title=Funnel for cathode ray tube}}</ref> The glass, known as CRT glass<ref>{{Cite web|url=https://ric.werecycle.eu/c/CRT_tubes_and_glass|title=6. CRT Glass|website=ric}}</ref><ref>{{Cite web|url=https://www.epa.gov/hw/frequent-questions-about-regulation-used-cathode-ray-tubes-crts-and-crt-glass|title=Frequent Questions About the Regulation of Used Cathode Ray Tubes (CRTs) and CRT Glass|date=22 February 2016|website=US EPA}}</ref> or TV glass,<ref>{{Cite book|url=https://books.google.com/books?id=MpQR01fTv7YC&q=tv+glass&pg=PA11|title=Quality Wars: The Triumphs and Defeats of American Business|first=Jeremy|last=Main|date=11 May 2010|publisher=Simon and Schuster|isbn=9781439138458|via=Google Books}}</ref> needs special properties to shield against x-rays while providing adequate light transmission in the screen or being very electrically insulating in the funnel and neck.  The formulation that gives the glass its properties is also known as the melt. The glass is of very high quality, being almost contaminant and defect free. Most of the costs associated with glass production come from the energy used to melt the raw materials into glass. Glass furnaces for CRT glass production have several taps to allow molds to be replaced without stopping the furnace, to allow production of CRTs of several sizes. Only the glass used on the screen needs to have precise optical properties.

The optical properties of the glass used on the screen affect color reproduction and purity in color CRTs. Transmittance, or how transparent the glass is, may be adjusted to be more transparent to certain colors (wavelengths) of light. Transmittance is measured at the center of the screen with a 546&nbsp;nm wavelength light, and a 10.16mm thick screen. Transmittance goes down with increasing thickness. Standard transmittances for Color CRT screens are 86%, 73%, 57%, 46%, 42% and 30%. Lower transmittances are used to improve image contrast but they put more stress on the electron gun, requiring more power on the electron gun for a higher electron beam power to light the phosphors more brightly to compensate for the reduced transmittance.<ref name="auto94"/><ref name="auto4">{{cite web |url=http://gradllc.com/images/Def.pdf |archive-url=https://web.archive.org/web/20040909183710/http://gradllc.com/images/Def.pdf |archive-date=2004-09-09 |url-status=live |title= Deflection|website=gradllc.com |access-date=2020-12-11}}</ref> The transmittance must be uniform across the screen to ensure color purity. The radius (curvature) of screens has increased (grown less curved) over time, from 30 to 68 inches, ultimately evolving into completely flat screens, reducing reflections. The thickness of both curved<ref name="auto22">{{Cite web|url=http://www.lgphilips-displays.com:80/download/Catalogue-CDT.pdf|title=Catalogue-CDT|archive-url=https://web.archive.org/web/20030317014046/http://www.lgphilips-displays.com:80/download/Catalogue-CDT.pdf |archive-date=17 March 2003 }}</ref> and flat screens gradually increases from the center outwards, and with it, transmittance is gradually reduced. This means that flat-screen CRTs may not be completely flat on the inside.<ref name="auto22"/><ref>{{Cite patent |country=US |number=6806636B2 |url=https://patents.google.com/patent/US6806636B2/en|title=Flat CRT with improved coating}}</ref>

The glass used in CRTs arrives from the glass factory to the CRT factory as either separate screens and funnels with fused necks, for Color CRTs, or as bulbs made up of a fused screen, funnel and neck. There were several glass formulations for different types of CRTs, that were classified using codes specific to each glass manufacturer. The compositions of the melts were also specific to each manufacturer.<ref name="glassts">{{cite web |url=https://www.glass-ts.com/userfiles/files/2003-08%20New%20Approach%20to%20Cathode%20Ray%20Tube%20(CRT)%20Recycling.pdf |title=GW-12.10-130: NEW APPROACH TO CATHODE RAY TUBE (CRT) RECYCLING |date=2003 |website=www.glass-ts.com |access-date=2020-12-11 |archive-date=13 November 2020 |archive-url=https://web.archive.org/web/20201113001416/https://www.glass-ts.com/userfiles/files/2003-08%20New%20Approach%20to%20Cathode%20Ray%20Tube%20(CRT)%20Recycling.pdf |url-status=dead }}</ref> Those optimized for high color purity and contrast were doped with Neodymium, while those for monochrome CRTs were tinted to differing levels, depending on the formulation used and had transmittances of 42% or 30%.<ref name="auto38">{{cite web |url= https://spie.org/samples/TT54.pdf |archive-url=https://web.archive.org/web/20120907080716/http://spie.org/samples/TT54.pdf |archive-date=2012-09-07 |url-status=live|title= CRT Glass|website=spie.org |access-date=2020-12-11}}</ref> Purity is ensuring that the correct colors are activated (for example, ensuring that red is displayed uniformly across the screen) while convergence ensures that images are not distorted. Convergence may be modified using a cross hatch pattern.<ref name="auto85">{{Cite web|url=https://www.repairfaq.org/samnew/tvfaq/tvccrtssa.htm|title=SER FAQ: TVFAQ: Color CRTs - shadow masks and aperture grills|website=www.repairfaq.org}}</ref><ref name="auto48">{{Cite web|url=https://www.repairfaq.org/samnew/tvfaq/tvcrtcona.htm|title=SER FAQ: TVFAQ: CRT convergence adjustment|website=www.repairfaq.org}}</ref><ref>{{Cite web|url=https://www.mediacollege.com/video/test-patterns/convergence/|title=Convergence Test Patterns|website=www.mediacollege.com}}</ref>

CRT glass used to be made by dedicated companies<ref>{{Cite web|url=https://www.eetimes.com/corning-asahi-video-to-sell-plant-assets-to-chinese-supplier/|title=Corning Asahi Video to sell plant assets to Chinese supplier &#124; EE Times|date=10 June 2003 }}</ref> such as [[AGC Inc.]],<ref>{{Cite web|url=http://www.digitimes.com/news/a20060725A6027.html|title=CPT expects limited impact from Asahi Glass CRT plant closure in Taiwan|website=DIGITIMES|date=25 July 2006 }}</ref><ref>{{Cite web|url=https://www.glassonline.com/asahi-techno-vision-to-close-singapore-plant/|title=Asahi Techno Vision to close Singapore plant|date=12 June 2007}}</ref><ref>{{Cite web|url=https://www.glassonline.com/asahi-glass-restructures-crt-funnel-manufacturing/|title=Asahi Glass restructures CRT funnel manufacturing|date=13 January 2005}}</ref> [[O-I Glass]],<ref>{{Cite web|url=https://www.neg.co.jp/en/company/history/|title=History|website=Nippon Electric Glass Co., Ltd.}}</ref> Samsung Corning Precision Materials,<ref>{{Cite web|url=https://www.koreatimes.co.kr/www/tech/2020/12/693_100541.html|title=4 CRT glass makers fined for price fixing|date=11 December 2011|website=koreatimes}}</ref> [[Corning Inc.]],<ref>{{Cite web|url=https://www.photonics.com/Articles/Corning_to_Close_Plant_and_Cut_1000_Jobs/a15760|title=Corning to Close Plant and Cut 1000 Jobs|website=www.photonics.com}}</ref><ref>{{Cite web|url=https://www.zdnet.com/article/corning-to-close-tv-glass-plant/|title=Corning to close TV glass plant|first=Richard|last=Shim|website=ZDNet}}</ref> and [[Nippon Electric Glass]];<ref>{{Cite web|url=https://www.bcnretail.com/news/detail/050901_2045.html|title=日本電気硝子、CRT用ガラスの国内生産を9月末で停止、国内需要の消滅に対応|website=BCN＋R}}</ref> others such as Videocon, Sony for the US market and Thomson made their own glass.<ref name="auto72">{{Cite web|url=https://resource-recycling.com/e-scrap/2016/03/03/videocon-begins-accepting-crt-glass-again/|title=Videocon begins accepting CRT glass again|first=Bobby|last=Elliott|date=3 March 2016}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=BAmBhJta85wC&q=thomson+picture+tube&pg=PA4|title=Industry and Trade Summary: Television Picture Tubes and other Cathode-Ray Tubes|publisher=DIANE Publishing|isbn=9781457825903|via=Google Books}}</ref><ref>{{Cite web|url=http://archive.glassonline.com/site/news/topic/Sector-trends/id/4797/American-Video-Glass-Company-TV-glass-plant-officially-dedicated|title=American Video Glass Company: TV glass plant officially dedicated|website=archive.glassonline.com|access-date=8 December 2020|archive-date=21 October 2021|archive-url=https://web.archive.org/web/20211021165012/http://archive.glassonline.com/site/news/topic/Sector-trends/id/4797/American-Video-Glass-Company-TV-glass-plant-officially-dedicated|url-status=dead}}</ref><ref>{{cite web |url=https://www.bizjournals.com/pittsburgh/stories/2006/12/04/daily32.html |title= Daily stories|website=2006 www.bizjournals.com|access-date=2020-12-11}}</ref><ref name="auto95">{{Cite web|url=http://www.gic.jp/museum/tv_tale/tv_tale02.html|title=テレビ今昔物語|website=www.gic.jp}}</ref>

The funnel and the neck are made of leaded potash-soda glass or lead silicate glass<ref name="auto50"/> formulation to shield against x-rays generated by high voltage electrons as they decelerate after striking a target, such as the phosphor screen or [[shadow mask]] of a color CRT. The velocity of the electrons depends on the anode voltage of the CRT; the higher the voltage, the higher the speed.<ref name="auto2">{{Cite web|url=https://www2.physics.ox.ac.uk/accelerate/resources/demonstrations/cathode-ray-tube|title=Cathode ray tube &#124; University of Oxford Department of Physics|website=www2.physics.ox.ac.uk}}</ref> The amount of x-rays emitted by a CRT can also lowered by reducing the brightness of the image.<ref>{{Cite web|url=http://repairfaq.cis.upenn.edu/Misc/samnew/tvfaq/tvsibwaxray.htm|title=SER FAQ: TVFAQ: Should I be worried about X-ray exposure while servicing a TV or monitor?|website=repairfaq.cis.upenn.edu|access-date=8 December 2020|archive-date=1 November 2020|archive-url=https://web.archive.org/web/20201101031818/http://repairfaq.cis.upenn.edu/Misc/samnew/tvfaq/tvsibwaxray.htm|url-status=dead}}</ref><ref>{{Cite web|url=http://repairfaq.cis.upenn.edu/Misc/samnew/tvfaq/tvxrayoem.htm|title=SER FAQ: TVFAQ: X-ray and other EM emission from my TV or monitor?|website=repairfaq.cis.upenn.edu|access-date=8 December 2020|archive-date=1 November 2020|archive-url=https://web.archive.org/web/20201101131639/http://repairfaq.cis.upenn.edu/Misc/samnew/tvfaq/tvxrayoem.htm|url-status=dead}}</ref><ref name="auto35">{{Cite magazine|title=X-Rays from TV Sets - Are They Harmful? <!--https://www.rfcafe.com/references/radio-news/tv-set-x-rays-radio-tv-news-november-1958.htm-->|date=November 1958|magazine=Radio News}}</ref><ref name="auto104"/> Leaded glass is used because it is inexpensive,<ref name="auto1">{{Cite web|url=https://patents.google.com/patent/JP2000128571A/en?q=(cathode+ray+tube+lead+glass+economical)&oq=cathode+ray+tube+lead+glass+economical&page=1|title=陰極線管用のガラス組成物および陰極線管}}</ref> while also shielding heavily against x-rays, although some funnels may also contain barium.<ref name="Lee & Hsi 2002">{{cite journal |last1=Lee |first1=Ching-Hwa |last2=Hsi |first2=Chi-Shiung |title=Recycling of Scrap Cathode Ray Tubes |journal=Environmental Science & Technology |date=1 January 2002 |volume=36 |issue=1 |pages=69–75 |doi=10.1021/es010517q |pmid=11811492 |bibcode=2002EnST...36...69L }}</ref><ref>{{Cite book|url=https://books.google.com/books?id=z4Ha0AYdon4C&q=cathode+ray+tube+funnel+lead+glass+inexpensive&pg=PA57|title=Lead-free Electronics|first1=Sanka|last1=Ganesan|first2=Michael G.|last2=Pecht|date=31 March 2006|publisher=John Wiley & Sons|isbn=9780470007792|via=Google Books}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=FvkqeL4IDMwC&q=cathode+ray+tube+funnel+lead+glass+inexpensive&pg=PA5|title=Image Performance in CRT Displays|first=Kenneth|last=Compton|date=5 December 2003|publisher=SPIE Press|isbn=9780819441447|via=Google Books}}</ref><ref name="auto38"/> The screen is usually instead made out of a special lead-free silicate<ref name="auto50"/> glass formulation with barium and strontium to shield against x-rays, as it doesn't brown unlike glass containing lead.<ref name="auto1"/><ref>{{Cite book|url=https://books.google.com/books?id=nGsoDwAAQBAJ&dq=crt+glass+browning&pg=RA1-PA5|title=Introduction to Glass Science and Technology|first=James E.|last=Shelby|date=6 November 2015|publisher=Royal Society of Chemistry|isbn=978-1-78262-511-7 |via=Google Books}}</ref> Another glass formulation uses 2–3% of [[lead]] on the screen.<ref name="auto104"/> Alternatively zirconium can also be used on the screen in combination with barium, instead of lead.<ref>{{cite book | url=https://books.google.com/books?id=T1NS5wI3H4UC&dq=projection+crt+radiation+browning&pg=PA227 | isbn=978-0-306-44191-2 | title=Color in Electronic Displays | date=30 April 1992 | publisher=Springer }}</ref>
[[File:Old TV3.jpg|thumb|Soviet TV set from 1960s photographed from backside]]

Monochrome CRTs may have a tinted barium-lead glass formulation in both the screen and funnel, with a potash-soda lead glass in the neck; the potash-soda and barium-lead formulations have different thermal expansion coefficients. The glass used in the neck must be an excellent electrical insulator to contain the voltages used in the electron optics of the electron gun, such as focusing lenses. The lead in the glass causes it to brown (darken) with use due to x-rays, usually the CRT cathode wears out due to cathode poisoning before browning becomes apparent. The glass formulation determines the highest possible anode voltage and hence the maximum possible CRT screen size. For color, maximum voltages are often 24–32&nbsp;kV, while for [[monochrome]] it is usually 21 or 24.5&nbsp;kV,<ref name="auto63">{{Cite book|url=https://books.google.com/books?id=FvkqeL4IDMwC&q=crt+venting&pg=PA9|title=Image Performance in CRT Displays|first=Kenneth|last=Compton|date=5 December 2003|publisher=SPIE Press|isbn=9780819441447|via=Google Books}}</ref> limiting the size of monochrome CRTs to 21&nbsp;inches, or ~1&nbsp;kV per inch. The voltage needed depends on the size and type of CRT.<ref name="auto3">{{Cite patent |country=US |number=5096445A |url=https://patents.google.com/patent/US5096445A/en|title=Anode connector assembly for a cathode ray tube}}</ref> Since the formulations are different, they must be compatible with one another, having similar thermal expansion coefficients.<ref name="auto38"/> The screen may also have an anti-glare or anti-reflective coating,<ref>{{Cite patent |country=US |number=5404073A |url=https://patents.google.com/patent/US5404073A/no|title=Antiglare/antistatic coating for CRT}}</ref><ref name="auto4"/><ref>{{Cite web|url=https://www.tomshardware.com/reviews/comparison,440.html|title=Comparison: Twelve 19" CRT Monitors|first=Philippe|last=Ramelet|date=March 19, 2002|website=Tom's Hardware}}</ref> or be ground to prevent reflections.<ref>{{Cite patent |country=US |number=4884006A |url=https://patents.google.com/patent/US4884006A/en |title=Inner surface specular reflection suppression in flat CRT faceplate}}</ref> CRTs may also have an anti-static coating.<ref name="auto4"/><ref>{{Cite patent |country=US |number=6590352B1 |url=https://patents.google.com/patent/US6590352B1/en|title=Electrical grounding of CRT antistatic/antireflective coating}}</ref><ref name="auto94"/>

The leaded glass in the funnels of CRTs may contain 21–25% of [[lead oxide]] (PbO),<ref name="auto81">{{Cite patent |country=US |number=6163106A |url=https://patents.google.com/patent/US6163106A/en|title=Color cathode ray tube and water resistant glass frit}}</ref><ref>{{cite web |url=https://ipen.org/sites/default/files/documents/Looking-through-glass-CRT-recycling-in-India.pdf |archive-url=https://web.archive.org/web/20201001051655/https://ipen.org/sites/default/files/documents/Looking-through-glass-CRT-recycling-in-India.pdf |archive-date=2020-10-01 |url-status=live |title= Looking through the glass|website=ipen.org |access-date=2020-12-11}}</ref><ref name="glassts"/> The neck may contain 30–40% of lead oxide,<ref>{{Cite web |url=https://www.glass-ts.com/userfiles/files/2003-08%2520New%2520Approach%2520to%2520Cathode%2520Ray%2520Tube%2520(CRT)%2520Recycling.pdf |title=Archived copy |access-date=20 February 2021 |archive-date=7 March 2021 |archive-url=https://web.archive.org/web/20210307115851/https://www.glass-ts.com/userfiles/files/2003-08%20New%20Approach%20to%20Cathode%20Ray%20Tube%20(CRT)%20Recycling.pdf |url-status=dead }}</ref><ref>{{cite journal |last1=Xu |first1=Qingbo |last2=Li |first2=Guangming |last3=He |first3=Wenzhi |last4=Huang |first4=Juwen |last5=Shi |first5=Xiang |title=Cathode ray tube (CRT) recycling: Current capabilities in China and research progress |journal=Waste Management |date=August 2012 |volume=32 |issue=8 |pages=1566–1574 |doi=10.1016/j.wasman.2012.03.009 |pmid=22542858 |bibcode=2012WaMan..32.1566X }}</ref> and the screen may contain 12% of [[barium oxide]], and 12% of [[strontium oxide]].<ref name="auto50"/> A typical CRT contains several kilograms of lead as lead oxide in the glass<ref name="auto73"/> depending on its size; 12 inch CRTs contain 0.5&nbsp;kg of lead in total while 32&nbsp;inch CRTs contain up to 3&nbsp;kg.<ref name="auto50"/> Strontium oxide began being used in CRTs, its major application, in the 1970s.<ref>{{cite web|url = http://minerals.usgs.gov/minerals/pubs/commodity/strontium/myb1-2007-stron.pdf|title = Mineral Yearbook 2007:Strontium|first1 = Joyce A.|last1 = Ober|first2 = Désirée E.|last2 = Polyak|publisher = United States Geological Survey|access-date = 2009-09-14}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=G6c7AQAAMAAJ&q=faceplate+glass+production+%2C+strontium%27s+major+end+use+since+the+early+1970s&pg=RA6-SA74-PA1|title=Minerals Yearbook|date=8 May 2011|publisher=Bureau of Mines|isbn=9781411332270|via=Google Books}}</ref> Before this, CRTs used lead on the faceplate.<ref name="auto74"/>

Some early CRTs used a metal funnel insulated with polyethylene instead of glass with conductive material.<ref name="auto59"/> Others had ceramic or blown Pyrex instead of pressed glass funnels.<ref>{{Cite web|url=https://www.earlytelevision.org/racs_pyrex_rebuild.html|title=RACS - Pyrex CRT Rebuilding|website=www.earlytelevision.org}}</ref><ref>{{cite web |url=http://www.nostalgiatech.co.uk/GB470885A.pdf |archive-url=https://web.archive.org/web/20191221202059/http://www.nostalgiatech.co.uk/GB470885A.pdf |archive-date=2019-12-21 |url-status=live |title= Patent specs|website= www.nostalgiatech.co.uk|access-date=2020-12-11}}</ref><ref name="auto30"/><ref>{{cite web |url=https://vintagetek.org/ceramic-strips/ |title=Ceramic strips |website=vintagetek.org |format=PDF|access-date=2020-12-11}}</ref><ref name="auto69">{{Cite web|url=https://www.crtsite.com/oscilloscope-crt.html|title=The Cathode Ray Tube site. oscilloscope crt's|website=www.crtsite.com}}</ref> Early CRTs did not have a dedicated anode cap connection; the funnel was the anode connection, so it was live during operation.<ref name="auto53">{{Cite web|url=https://www.oldtellys.co.uk/otmonotube.html|title=The Monochrome Tube|website=www.oldtellys.co.uk}}</ref>

The funnel is coated on the inside and outside with a conductive coating,<ref name="auto60">{{Cite web|url=http://repairfaq.cis.upenn.edu/samnew/tvfaq/tvaiodc.htm|title=SER FAQ: TVFAQ: Additional information on discharging CRTs|website=repairfaq.cis.upenn.edu|access-date=8 December 2020|archive-date=1 November 2020|archive-url=https://web.archive.org/web/20201101104218/http://repairfaq.cis.upenn.edu/samnew/tvfaq/tvaiodc.htm|url-status=dead}}</ref><ref name="auto7">{{cite web |title=Manual |url=https://wiki.arcadeotaku.com/images/c/c6/Toei_TC-L292K_Manual.pdf |url-status=live |archive-url=https://web.archive.org/web/20201110232957/https://wiki.arcadeotaku.com/images/c/c6/Toei_TC-L292K_Manual.pdf |archive-date=2020-11-10 |access-date=2020-12-11 |website=wiki.arcadeotaku.com |language=JA}}</ref> making the funnel a capacitor, helping stabilize and filter the anode voltage of the CRT, and significantly reducing the amount of time needed to turn on a CRT. The stability provided by the coating solved problems inherent to early power supply designs, as they used vacuum tubes. Because the funnel is used as a capacitor, the glass used in the funnel must be an excellent electrical insulator ([[dielectric]]). The inner coating has a positive voltage (the anode voltage that can be several kV) while the outer coating is connected to ground. CRTs powered by more modern power supplies do not need to be connected to [[Ground (electricity)|ground]], due to the more robust design of modern power supplies. The value of the capacitor formed by the funnel is 5–10&nbsp;[[Nanofarad|nF]], although at the voltage the anode is normally supplied with. The capacitor formed by the funnel can also suffer from [[dielectric absorption]], similarly to other types of capacitors.<ref>{{Cite web|url=http://www.repairfaq.org/sam/crtfaq.htm|title=TV and Monitor CRT (Picture Tube) Information|website=www.repairfaq.org}}
{{Cite patent |country=US |number=3614519A |url=https://patents.google.com/patent/US3614519A/en |title=Cathode-ray tube magnetic shield}}
{{Cite patent |country=US |number=3802757A |url=https://patents.google.com/patent/US3802757A/en |title=Method of fabricating a cathode ray tube having a conductive metallic coating therein}}</ref><ref name="auto63"/><ref name="auto67">{{Cite web|url=http://www.r-type.org/exhib/aar0020.htm|title=40CB4 @ The Valve Museum|website=www.r-type.org}}</ref><ref name="auto29">{{Cite patent |country=US |number=5104686A |url=https://patents.google.com/patent/US5104686A/en |title=CRT funnel coating apparatus and method}}</ref><ref name="auto60"/><ref name="auto38"/> Because of this CRTs have to be discharged<ref name="auto15">{{cite web |url=http://www.crtsolutions.com/CRTSafety.pdf |archive-url=https://web.archive.org/web/20120617143458/http://www.crtsolutions.com/CRTSafety.pdf |archive-date=2012-06-17 |url-status=live |title= CRT Safety |website=www.crtsolutions.com |access-date=2020-12-11}}</ref> before handling to prevent injury.

The depth of a CRT is related to its screen size.<ref name="auto79">{{cite web |url=https://eti.pg.edu.pl/documents/176568/264302/module%202%20cathode%20ray%20tube.doc |title= Data|website= eti.pg.edu.pl|access-date=2020-12-11}}</ref> Usual deflection angles were 90° for computer monitor CRTs and small CRTs and 110° which was the standard in larger TV CRTs, with 120 or 125° being used in slim CRTs made since 2001–2005 in an attempt to compete with LCD TVs.<ref>Practical Television, November 2001 issue <!--https://worldradiohistory.com/hd2/IDX-UK/Technology/Technology-All-Eras/Archive-Practical-Television-IDX/00s/Television-2001-11-OCR-Page-0006.pdf--> 120° deflection
{{Cite patent |country=CN |number=101253599A |url=https://patents.google.com/patent/CN101253599A/en |title=High deflection angle CRT display }}
{{Cite web|url=http://repairfaq.cis.upenn.edu/sam/crtfaq.htm|title=TV and Monitor CRT (Picture Tube) Information|website=repairfaq.cis.upenn.edu|access-date=8 December 2020|archive-date=22 November 2020|archive-url=https://web.archive.org/web/20201122100132/http://repairfaq.cis.upenn.edu/sam/crtfaq.htm|url-status=dead}} 90 degrees in monitors, 110 in TVs</ref><ref name="auto4"/><ref name="auto9"/><ref name="auto34"/><ref name="auto45">{{Cite web|url=http://www.r-type.org/exhib/aac0001.htm|title=M14-170W @ The Valve Museum|website=www.r-type.org}}</ref> Over time, deflection angles increased as they became practical, from 50° in 1938 to 110° in 1959,<ref name="auto68"/> and 125° in the 2000s. 140° deflection CRTs were researched but never commercialized, as convergence{{Clarification needed|reason=What does "convergence" mean here?|date=December 2023}} problems were never resolved.<ref>{{Cite web|url=https://www.earlytelevision.org/color_crts.html|title=Color Picture Tubes|website=www.earlytelevision.org}}</ref>
<gallery mode="packed" heights="180px">
File:Cinescopio per televisore a schermo rettangolare, 17 pollici, deflessione 110°, bianco e nero - Museo scienza tecnologia Milano 10081 dia.jpg|A monochrome CRT with 110° deflection
File:Cinescopio per televisore a schermo rettangolare, 13 pollici, deflessione 90°, bianco e nero - Museo scienza tecnologia Milano 10082 dia.jpg|A monochrome CRT with 90° deflection
</gallery>

===Size and weight===
The size of a CRT can be measured by the screen's ''entire'' [[area]] (or [[face diagonal]]) or alternatively by only its ''viewable'' area (or diagonal) that is coated by phosphor and surrounded by black edges.<ref name="auto7"/><ref>{{cite web |url= https://wiki.arcadeotaku.com/images/c/c6/Crt.jpg|title=Diagram |website=wiki.arcadeotaku.com |format=PDF|access-date=2020-12-11}}</ref>

While the viewable area may be rectangular, the edges of the CRT may have a curvature (e.g. black stripe CRTs, first made by Toshiba in 1972)<ref name="auto95" /> or the edges may be black and truly flat (e.g. Flatron CRTs),<ref name="auto22" /><ref name="auto95" /><ref>{{Cite web|url=http://www.lgphilips-displays.com/download/ezFlat_HB.pdf|date=17 March 2003|archive-url=https://web.archive.org/web/20030317014636/http://www.lgphilips-displays.com/download/ezFlat_HB.pdf|title=data|archive-date=17 March 2003}}
https://dinaspajak.com/wp-content/uploads/2023/09/368434_LRG_DSC04662.jpg <!--bare CRT front, featured here: https://hardforum.com/threads/24-widescreen-crt-fw900-from-ebay-arrived-comments.952788/page-438--></ref> or the viewable area may follow the curvature of the edges of the CRT (with or without black edges or curved edges).<ref>{{cite web |url= http://www.earlytelevision.org/pdf/rca_lancaster_color_tv_conversion_power_tubes.pdf |archive-url=https://web.archive.org/web/20210306010139/http://www.earlytelevision.org/pdf/rca_lancaster_color_tv_conversion_power_tubes.pdf |archive-date=2021-03-06 |url-status=live|title=Electron Tubes: A Constant Challenge |website=www.earlytelevision.org |access-date=2020-12-11}}</ref><ref>{{cite web |url=https://frank.pocnet.net/sheets/202/2/23EGP22.pdf |archive-url=https://web.archive.org/web/20170726234224/http://frank.pocnet.net/sheets/202/2/23EGP22.pdf |archive-date=2017-07-26 |url-status=live |title= Factsheet |website=frank.pocnet.net|access-date=2020-12-11}}</ref><ref name="auto52" />

Small CRTs below 3&nbsp;inches were made for [[handheld TV]]s such as the [[MTV-1]] and viewfinders in camcorders. In these, there may be no black edges, that are however truly flat.<ref>{{Cite web|url=http://lampes-et-tubes.info/cr/cr028.php?l=e|title=Matsushita 40CB4 1.5" Viewfinder CRT|website=lampes-et-tubes.info}}</ref><ref name="auto67" /><ref>{{Cite web|url=https://www.crtsite.com/tv-crt.html|title=The Cathode ray Tube site. Television CRT's|website=www.crtsite.com}}</ref><ref>{{Cite web|url=http://www.earlytelevision.org/small_trinitron.html|title=World's Smallest Trinitron|website=www.earlytelevision.org}}</ref><ref>{{Cite web|url=https://visions4netjournal.com/indextron/|title=Indextron|date=29 December 2016|website=Visions4 Magazine}}</ref>

Most of the weight of a CRT comes from the thick glass screen, which comprises 65% of the total weight of a CRT and limits its practical size (see {{Slink|Cathode-ray tube|Size|nopage=y}}). The funnel and neck glass comprise the remaining 30% and 5% respectively. The glass in the funnel can vary in thickness, to join the thin neck with the thick screen.<ref>{{Cite web|url=https://patents.google.com/patent/US7355331B2/en?q=(Cathode+ray+tube+funnel+thickness)&oq=Cathode+ray+tube+funnel+thickness|title=Cathode-ray tube apparatus}}</ref><ref>{{Cite web|url=https://patents.google.com/patent/US6323591B1/en?q=(Cathode+ray+tube+skirt)&oq=Cathode+ray+tube+skirt|title=CRT with specific envelope thickness}}</ref><ref name="auto50"/><ref name="auto76"/> Chemically or thermally tempered glass may be used to reduce the weight of the CRT glass.<ref>{{cite journal |first1=Tsunehiko |last1=Sugawara |first2=Yuichi |last2=Kuroki |first3=Tetsuji |last3=Yano |first4=Shuichi |last4=Shibata |title=Recent Advances in Strengthening Glass Material for CRT |journal=Information and Media Technologies |volume=1 |issue=1 |year=2006 |pages=1–6 |doi=10.11185/imt.1.1 }}</ref><ref>{{cite journal |last1=Sugawara |first1=Tsunehiko |last2=Shimizu |first2=Naoya |last3=Murakami |first3=Toshide |title=Recent Developments in Reducing Bulkiness of CRT Glass Bulbs |journal=한국정보디스플레이학회:학술대회논문집 |date=2002 |pages=359–363 |url=https://www.koreascience.or.kr/article/CFKO200224282627610.page }}</ref><ref>{{cite web |url=http://var.glassonline.com/uploads/publications/section_articles/articlePDF/asahiglassgti1-99.pdf |archive-url=https://web.archive.org/web/20201116230236/http://var.glassonline.com/uploads/publications/section_articles/articlePDF/asahiglassgti1-99.pdf |archive-date=2020-11-16 |url-status=live |title= Asahi glass |website= var.glassonline.com|access-date=2020-12-11}}</ref><ref>{{Cite patent |country=JP |number=2004339019A |url=https://patents.google.com/patent/JP2004339019A/en|title=Tempered glass component and vacuum envelope for display using it}}</ref>

===Anode===  <!--Expand: how anode voltage is derived from horizontal deflection circuitry, the horiz. deflection coil and its voltage, which is created by the flyback so it creates anode voltage that is then multiplied and fed and horiz. deflection coil voltage that contributes to anode voltage, maybe flyback first creates 120v horiz. high current voltage, goes to the coil, returns from the coil, then its fed and voltage multiplied and energy added and fed to the anode-->
The outer conductive coating is connected to ground while the inner conductive coating is connected using the anode button/cap through a series of capacitors and diodes (a [[Cockcroft–Walton generator]]) to the high voltage [[flyback transformer]]; the inner coating is the anode of the CRT,<ref name="auto54">{{cite web |url=https://worldradiohistory.com/hd2/IDX-Business/Books/Regulation/IDX/Radio-Operating-Questions-&-Answers-12th-OCR-Page-0494.pdf |archive-url=https://web.archive.org/web/20210306171748/https://worldradiohistory.com/hd2/IDX-Business/Books/Regulation/IDX/Radio-Operating-Questions-&-Answers-12th-OCR-Page-0494.pdf |archive-date=2021-03-06 |url-status=live |title=Radio operating Q&A |website= worldradiohistory.com|access-date=2020-12-11}}</ref> which, together with an electrode in the electron gun, is also known as the final anode.<ref>{{Cite patent |country=US |number=7071605B2 |url=https://patents.google.com/patent/US7071605B2/en |title=Cathode structure for color cathode ray tube}}</ref><ref name="auto6">{{Cite book|author= Thorn-AEI Radio Valves and Tubes Limited <!--http://www.r-type.org/articles/art-004f.htm-->|title=Electrons in Shadow-mask Colour Tubes|location= United Kingdom|date=1968}}</ref> The inner coating is connected to the electrode using springs. The electrode forms part of a bipotential lens.<ref name="auto6"/><ref name="auto11">{{Cite patent |country=US |number=5196764A |url=https://patents.google.com/patent/US5196764A/en |title=Cathode ray tube having symmetrical anode potential}}</ref> The capacitors and diodes serve as a [[voltage multiplier]] for the current delivered by the flyback.

For the inner funnel coating, monochrome CRTs use aluminum while color CRTs use [[aquadag]];<ref name="auto38"/> Some CRTs may use iron oxide on the inside.<ref name="auto50"/> On the outside, most CRTs (but not all)<ref>https://www.crtsite.com/radar-crt.html there is no matte black coating on the outside of the CRT so here is no aquadag on the outside</ref> use aquadag.<ref>{{Cite book|url=https://books.google.com/books?id=90GZPA-hCuMC&q=crt+aquadag+outer+outside&pg=PA134|title=Newnes Guide to Television and Video Technology: The Guide for the Digital Age - from HDTV, DVD and flat-screen technologies to Multimedia Broadcasting, Mobile TV and Blu Ray|first=K. F.|last=Ibrahim|date=14 September 2007|publisher=Elsevier|isbn=9780080550664|via=Google Books}}</ref> Aquadag is an electrically conductive graphite-based paint. In color CRTs, the aquadag is sprayed onto the interior of the funnel<ref>{{Cite patent |country=US |number=3791846A |url=https://patents.google.com/patent/US3791846A/en |title=Method for applying an internal coating to a cathode ray tube}}</ref><ref name="auto38"/> whereas historically aquadag was painted into the interior of monochrome CRTs.<ref name="auto68"/>

The anode is used to accelerate the electrons towards the screen and also collects the secondary electrons that are emitted by the phosphor particles in the vacuum of the CRT.<ref>{{cite web | first=Kirt|last=Blattenberger | title=Navy Electricity and Electronics Training Series (NEETS), Module 6 | website=RF Cafe | url=https://www.rfcafe.com/references/electrical/NEETS-Modules/NEETS-Module-06-2-21-2-30.htm | access-date=2020-12-11}} <!--US military source--></ref><ref name="auto70">{{Cite patent |country=US |number=2582822A |url=https://patents.google.com/patent/US2582822A/en |title=Cathode-ray tube with aluminized screen}}</ref><ref>{{Cite web|url=https://electronicscoach.com/cathode-ray-tube-c-r-t.html|title=What is CRT (Cathode Ray Tube)? definition, block diagram and working of CRT|date=19 May 2018}}</ref><ref name="auto82">{{cite journal |last1=Ozawa |first1=Lyuji |title=Electron flow route at phosphor screens in CRTs |journal=Materials Chemistry and Physics |date=15 January 2002 |volume=73 |issue=2 |pages=144–150 |doi=10.1016/s0254-0584(01)00360-1 }}</ref><ref name="auto68"/>

The anode cap connection in modern CRTs must be able to handle up to 55–60kV depending on the size and brightness of the CRT. Higher voltages allow for larger CRTs, higher image brightness, or a tradeoff between the two.<ref name="auto36">{{cite journal |last1=Solomos |first1=E. |title=A projection graphic display for the computer aided analysis of bubble chamber images |journal=Nuclear Instruments and Methods |date=20 December 1979 |volume=167 |issue=2 |pages=305–311 |doi=10.1016/0029-554X(79)90019-3 |bibcode=1979NucIM.167..305S |url=https://cds.cern.ch/record/133614 }}</ref><ref name="auto3"/> It consists of a metal clip that expands on the inside of an anode button that is embedded on the funnel glass of the CRT.<ref name="auto16">{{Cite patent |country=US |number=5583392A |url=https://patents.google.com/patent/US5583392A/en |title=CRT anode cap}}</ref><ref>{{Cite web|url=https://www.petervis.com/electronics%20guides/Sony%20KV-36FS76U/final-anode.html|title=Final Anode|accessdate=18 December 2022}}</ref> The connection is insulated by a silicone suction cup, possibly also using silicone grease to prevent [[corona discharge]].<ref>{{Cite web|url=http://repairfaq.cis.upenn.edu/Misc/samnew/tvfaq/tvasocfcrt.htm|title=SER FAQ: TVFAQ: Arcing, sparking, or corona from CRT HV anode (red wire/suction cup)|website=repairfaq.cis.upenn.edu|access-date=8 December 2020|archive-date=30 October 2020|archive-url=https://web.archive.org/web/20201030212335/http://repairfaq.cis.upenn.edu/Misc/samnew/tvfaq/tvasocfcrt.htm|url-status=dead}}</ref><ref>{{Cite web|url=https://www.repairfaq.org/samnew/tvfaq/tvrchvc.htm|title=SER FAQ: TVFAQ: Removing the CRT HV connector|website=www.repairfaq.org}}</ref>

The anode button must be specially shaped to establish a hermetic seal between the button and funnel. X-rays may leak through the anode button, although that may not be the case in newer CRTs starting from the late 1970s to early 1980s, thanks to a new button and clip design.<ref name="auto3"/><ref>{{cite web | url=https://patents.google.com/patent/DE2833485C2/en?q=(Crt+anode+nickel+cup)&assignee=Toshiba&oq=Crt+anode+nickel+cup+Toshiba+ | title=Anodenknopf für eine Kathodenstrahlröhre }}</ref> The button may consist of a set of 3 nested cups, with the outermost cup being made of a Nickel–Chromium–Iron alloy containing 40–49% of Nickel and 3–6% of Chromium to make the button easy to fuse to the funnel glass, with a first inner cup made of thick inexpensive iron to shield against x-rays, and with the second innermost cup also being made of iron or any other electrically conductive metal to connect to the clip. The cups must be heat resistant enough and have similar thermal expansion coefficients similar to that of the funnel glass to withstand being fused to the funnel glass. The inner side of the button is connected to the inner conductive coating of the CRT.<ref name="auto70"/> The anode button may be attached to the funnel while its being pressed into shape in a mold.<ref>{{Cite patent |country=KR |number=20000050533A |url=https://patents.google.com/patent/KR20000050533A/en |title=Apparatus for fusion-welding anode button to crt funnel}}
{{Cite web|url=https://books.google.com/books?id=oaWc_Z7Y-A8C&q=crt+glass+funnel+press+mold&pg=PA200|title=Official Gazette of the United States Patent Office|publisher=United States Patent Office|date=5 December 1969|via=Google Books}} press
{{Cite patent |country=US |number=4198588A |url=https://patents.google.com/patent/US4198588A/en |title=Anode button for a cathode ray tube}} nested design
{{Cite patent |country=US |number=4155614A |url=https://patents.google.com/patent/US4155614A/en |title=Connector assembly for anode button of a cathode ray tube}} clip and cap design, x-rays</ref><ref name="auto24">{{Cite patent |country=US |number=4422707A |url=https://patents.google.com/patent/US4422707A/en |title=CRT Anode cap}}</ref><ref name="auto3"/> Alternatively, the x-ray shielding may instead be built into the clip.<ref>{{Cite patent |country=US |number=4894023A |url=https://patents.google.com/patent/US4894023A/en |title=Connector assembly for anode ring of cathode ray tube}}</ref>

The flyback transformer is also known as an IHVT (Integrated High Voltage Transformer) if it includes a voltage multiplier. The flyback uses a ceramic or powdered iron core to enable efficient operation at high frequencies. The flyback contains one primary and many secondary windings that provide several different voltages. The main secondary winding supplies the voltage multiplier with voltage pulses to ultimately supply the CRT with the high anode voltage it uses, while the remaining windings supply the CRT's filament voltage, keying pulses, focus voltage and voltages derived from the scan raster. When the transformer is turned off, the flyback's magnetic field quickly collapses which induces high voltage in its windings. The speed at which the magnetic field collapses determines the voltage that is induced, so the voltage increases alongside its speed. A capacitor (Retrace Timing Capacitor) or series of capacitors (to provide redundancy) is used to slow the collapse of the magnetic field.<ref name="auto89" /><ref>{{Cite patent |country=US |number=4825129A |url=https://patents.google.com/patent/US4825129A/en |title=CRT focus tracking arrangement}}</ref>

The design of the high voltage power supply in a product using a CRT has an influence in the amount of x-rays emitted by the CRT. The amount of emitted x-rays increases with both higher voltages and currents. If the product such as a TV set uses an unregulated high voltage power supply, meaning that anode and focus voltage go down with increasing electron current when displaying a bright image, the amount of emitted x-rays is as its highest when the CRT is displaying a moderately bright images, since when displaying dark or bright images, the higher anode voltage counteracts the lower electron beam current and vice versa respectively. The high voltage regulator and rectifier vacuum tubes in some old CRT TV sets may also emit x-rays.<ref name="auto74">{{Cite magazine|title=TV X-Rays<!--http://www.rfcafe.com/references/radio-electronics/tv-x-rays-radio-electronics-april-1970.htm-->|date=April 1970|magazine=Radio Electronics}}</ref>

===Electron gun===
{{Main|Electron gun}}
The electron gun emits the electrons that ultimately hit the phosphors on the screen of the CRT. The electron gun contains a heater, which heats a cathode, which generates electrons that, using grids, are focused and ultimately accelerated into the screen of the CRT. The acceleration occurs in conjunction with the inner aluminum or aquadag coating of the CRT. The electron gun is positioned so that it aims at the center of the screen.<ref name="auto6"/> It is inside the neck of the CRT, and it is held together and mounted to the neck using glass beads or glass support rods, which are the glass strips on the electron gun.<ref name="auto68"/><ref name="auto6"/><ref>{{Cite patent |country=US |number=4409279A |url=https://patents.google.com/patent/US4409279A/en |title=Glass support rod for use in electron-gun mount assemblies}}</ref> The electron gun is made separately and then placed inside the neck through a process called "winding", or sealing.<ref name="auto37"/><ref>{{cite web | title=CRT Manufacturing | url=https://vintagetek.org/crt-manufacturing/ | access-date=2020-12-11}}</ref><ref name="auto83">{{Cite patent |country=US |number=4561874A |url=https://patents.google.com/patent/US4561874A/en |title=Method for heat sealing a gun mount in a CRT neck}}</ref><ref name="auto75">{{Cite web|url=http://www.lgphilips-displays.com/english/download/CPT_Manu_Process.pdf|title=Manual|date=2 May 2006|archive-url=https://web.archive.org/web/20060502053742/http://www.lgphilips-displays.com/english/download/CPT_Manu_Process.pdf|archive-date=2 May 2006}}</ref><ref>{{Cite web|url=https://www.earlytelevision.org/14ap4_construction.html|title=DuMont 14AP4|website=www.earlytelevision.org}}</ref><ref name="auto65">{{Cite web|url=https://venturebeat.com/2017/03/03/what-the-death-of-the-crt-display-technology-means-for-classic-arcade-machines/|title=Donkey Kong's failing liver: What the death of the CRT display technology means for classic arcade machines|date=3 March 2017}}</ref> The electron gun has a glass wafer that is fused to the neck of the CRT. The connections to the electron gun penetrate the glass wafer.<ref name="auto83"/><ref>{{Cite patent |country=US |number=6078134A |url=https://patents.google.com/patent/US6078134A/en |title=Narrow-neck CRT having a large stem pin circle}}</ref> Once the electron gun is inside the neck, its metal parts (grids) are arced between each other using high voltage to smooth any rough edges in a process called spot knocking, to prevent the rough edges in the grids from generating secondary electrons.<ref>{{Cite patent |country=EP |number=0634771B1 |url=https://patents.google.com/patent/EP0634771B1/un |title=Method for spot-knocking an electron gun assembly of a cathode ray tube}}</ref><ref>{{Cite patent |country=US |number=4883438A |url=https://patents.google.com/patent/US4883438A/en |title=Method for spot-knocking an electron gun mount assembly of a CRT}}</ref><ref>{{Cite patent |country=US |number=4457731A |url=https://patents.google.com/patent/US4457731A/en |title=Cathode ray tube processing}}</ref>

====Construction and method of operation====
The electron gun has an indirectly heated [[hot cathode]] that is heated by a tungsten filament heating element; the heater may draw 0.5–2&nbsp;A of current depending on the CRT. The voltage applied to the heater can affect the life of the CRT.<ref>Practical Television, June 2001 issue<!--https://worldradiohistory.com/hd2/IDX-UK/Technology/Technology-All-Eras/Archive-Practical-Television-IDX/00s/Television-2001-06-OCR-Page-0034.pdf--></ref><ref>{{cite web |url=https://elektrotanya.com/files/forum/2014/03/kepcsofutes-mero_[ET].pdf |title=CRT heater voltages|date=2001 |website=elektrotanya.com|access-date=2020-12-11}}</ref> Heating the cathode energizes the electrons in it, aiding electron emission,<ref name="auto77">{{Cite patent |country=JP |number=H07245056A |url=https://patents.google.com/patent/JPH07245056A/en |title=Indirectly heated cathode body structure for cathode-ray tube}}</ref> while at the same time current is supplied to the cathode; typically anywhere from 140&nbsp;mA at 1.5&nbsp;V to 600&nbsp;mA at 6.3&nbsp;V.<ref name="auto100">{{Cite web|url=https://electronicspost.com/function-of-electron-gun-assembly-in-crt-cathode-ray-tube/|title=Function of Electron Gun Assembly in CRT (Cathode Ray Tube)|date=16 November 2015}}</ref> The cathode creates an electron cloud (emits electrons) whose electrons are extracted, accelerated and focused into an electron beam.<ref name="auto68"/> Color CRTs have three cathodes: one for red, green and blue. The heater sits inside the cathode but does not touch it; the cathode has its own separate electrical connection. The cathode is a material coated onto a piece of nickel which provides the electrical connection and structural support; the heater sits inside this piece without touching it.<ref name="auto54"/><ref>{{Cite patent |country=US |number=4305188A |url=https://patents.google.com/patent/US4305188A/en |title=Method of manufacturing cathode assembly}}</ref><ref>{{Cite web|url=https://www.circuitstoday.com/crt-cathode-ray-tube|title=CRT-Cathode Ray Tube|date=25 September 2009}}</ref><ref>{{Cite magazine|last=Blackburn |first=A. P.|url=http://www.r-type.org/articles/art-116.htm |title=The Cathode-Ray Tube|magazine=The Radio Constructor|location= United Kingdom|date= August 1955}}</ref>

There are several [[short circuit]]s that can occur in a CRT electron gun. One is a heater-to-cathode short, that causes the cathode to permanently emit electrons which may cause an image with a bright red, green or blue tint with retrace lines, depending on the cathode (s) affected. Alternatively, the cathode may short to the control grid, possibly causing similar effects, or, the control grid and screen grid (G2)<ref>{{cite web |url=http://lateblt.tripod.com/bit71.txt |title=Principles Of A CRT |website=lateblt.tripod.com|access-date=2020-12-11}}</ref> can short causing a very dark image or no image at all. The cathode may be surrounded by a shield to prevent [[sputtering]].<ref>{{Cite patent |country=FR |number=2691577A1 |url=https://patents.google.com/patent/FR2691577A1/en |title=Cathode assembly for CRT electron gun - has protective screen around cathode emitter between emitter and hole in insulator support of cylindrical grid electrode}}</ref><ref name="auto">{{cite web |url= http://www.thegleam.com/ke5fx/crt/sencrt.pdf |archive-url=https://web.archive.org/web/20110422131015/http://www.thegleam.com/ke5fx/crt/sencrt.pdf |archive-date=2011-04-22 |url-status=live|title=Sencore Blows Away CRT Failures With CR7000 |last=Fromm |first= Randy |website= www.thegleam.com|access-date=2020-12-11}}</ref>

The cathode is a layer of barium oxide which is coated on a piece of nickel for electrical and mechanical support.<ref name="auto87">{{Cite patent |country=CN |number=1400621A |url=https://patents.google.com/patent/CN1400621A/en |title=Electronic tube cathode, long-life electronic tube tube and its making process}}</ref><ref name="auto63"/> The barium oxide must be activated by heating to enable it to release electrons. Activation is necessary because barium oxide is not stable in air, so it is applied to the cathode as barium carbonate, which cannot emit electrons. Activation heats the barium carbonate to decompose it into barium oxide and carbon dioxide while forming a thin layer of metallic barium on the cathode.<ref name=Gassler2016/><ref name="auto87"/> Activation is done when forming the vacuum (described in {{Slink|Cathode-ray tube|Evacuation|nopage=y}}). After activation, the oxide can become damaged by several common gases such as water vapor, carbon dioxide, and oxygen.<ref name="ba"/> Alternatively, barium strontium calcium carbonate may be used instead of barium carbonate, yielding barium, strontium and calcium oxides after activation.<ref>{{Cite patent |country=JP |number=2004022271A |url=https://patents.google.com/patent/JP2004022271A/en |title=Cathode-ray tube}}</ref><ref name="auto68"/> During operation, the barium oxide is heated to 800–1000°C, at which point it starts shedding electrons.<ref>{{Cite web|url=https://books.google.com/books?id=GwIAAAAAMBAJ&q=CRT+corner+convergence&pg=PT90|title=Maximum PC|date=5 August 1999|publisher=Future US|via=Google Books}}</ref><ref name="auto63"/><ref name="auto77"/>

Since it is a hot cathode, it is prone to cathode poisoning, which is the formation of a positive ion layer that prevents the cathode from emitting electrons, reducing image brightness significantly or completely and causing focus and intensity to be affected by the frequency of the video signal preventing detailed images from being displayed by the CRT. The positive ions come from leftover air molecules inside the CRT or from the cathode itself<ref name="auto68"/> that react over time with the surface of the hot cathode.<ref name="auto71">{{Cite web|url=http://www.ke5fx.com/crt.html|title=CRT Restoration for the (Brave) Experimenter|website=www.ke5fx.com}}</ref><ref name="auto"/> Reducing metals such as manganese, zirconium, magnesium, aluminum or titanium may be added to the piece of nickel to lengthen the life of the cathode, as during activation, the reducing metals diffuse into the barium oxide, improving its lifespan, especially at high electron beam currents.<ref>{{Cite patent |country=KR |number=100490170B1 |url=https://patents.google.com/patent/KR100490170B1/en |title=Cathode of CRT}}</ref> In color CRTs with red, green and blue cathodes, one or more cathodes may be affected independently of the others, causing total or partial loss of one or more colors.<ref name="auto"/> CRTs can wear or burn out due to cathode poisoning. Cathode poisoning is accelerated by increased cathode current (overdriving).<ref name="auto25">{{Cite web|url=https://www.extremetech.com/electronics/53826-crt-innovations/4|title=CRT Innovations - Page 4 of 7 - ExtremeTech|website=www.extremetech.com|access-date=8 December 2020|archive-date=6 October 2020|archive-url=https://web.archive.org/web/20201006072651/http://www.extremetech.com/electronics/53826-crt-innovations/4|url-status=dead}}</ref> In color CRTs, since there are three cathodes, one for red, green and blue, a single or more poisoned cathode may cause the partial or complete loss of one or more colors, tinting the image.<ref name="auto"/> The layer may also act as a capacitor in series with the cathode, inducing thermal lag. The cathode may instead be made of scandium oxide or incorporate it as a dopant, to delay cathode poisoning, extending the life of the cathode by up to 15%.<ref name="auto26">{{Cite web|url=https://www.extremetech.com/electronics/53826-crt-innovations/5|title=CRT Innovations - Page 5 of 7 - ExtremeTech|website=www.extremetech.com|access-date=8 December 2020|archive-date=1 November 2020|archive-url=https://web.archive.org/web/20201101022250/https://www.extremetech.com/electronics/53826-crt-innovations/5|url-status=dead}}</ref><ref name="auto63"/><ref>{{Cite book|url=https://books.google.com/books?id=FvkqeL4IDMwC&q=barium+oxide&pg=PA9|title=Image Performance in CRT Displays|first=Kenneth|last=Compton|date=5 December 2003|publisher=SPIE Press|isbn=9780819441447|via=Google Books}}</ref>

The rate of emission of electrons from the cathodes is related to their surface area. A cathode with more surface area creates more electrons, in a larger electron cloud, which makes focusing the electron cloud into an electron beam more difficult.<ref name="auto25"/> Normally, only a part of the cathode emits electrons unless the CRT displays images with parts that are at full image brightness; only the parts at full brightness cause all of the cathode to emit electrons. The area of the cathode that emits electrons grows from the center outwards as brightness increases, so cathode wear may be uneven. When only the center of the cathode is worn, the CRT may light brightly those parts of images that have full image brightness but not show darker parts of images at all, in such a case the CRT displays a poor gamma characteristic.<ref name="auto"/>

A voltage negative with respect to the cathode<ref>{{Cite book|url=https://books.google.com/books?id=gw8SBQAAQBAJ&q=crt+aluminized+screen&pg=PA129|title=Instrumentation Systems: Jones' Instrument Technology|first=B. E.|last=Noltingk|date=6 February 2016|publisher=Elsevier|isbn=9781483135601|via=Google Books}}</ref> is applied to the first (control) grid (G1) to control the emission of electrons into the rest of the electron gun. G1 in practice is a [[Wehnelt cylinder]].<ref name="auto100"/><ref>{{Cite web|url=https://www.radartutorial.eu/12.scopes/sc15.en.html|title=Radartutorial|website=www.radartutorial.eu}}</ref> The brightness of the image on the screen depends on both the anode voltage and the electron beam current and in practise the latter is constant, while the former is controlled by varying the difference in voltage between the cathode and the G1 control grid. The second (screen) grid of the gun (G2) then accelerates the electrons towards the screen using several hundred DC volts. Then a third grid (G3) electrostatically focuses the electron beam before it is deflected and later accelerated by the anode voltage onto the screen.<ref>{{Cite web|url=https://www.jmargolin.com/xy/xymon.htm|title=The Secret Life of XY Monitors|website=www.jmargolin.com}}</ref> Electrostatic focusing of the electron beam may be accomplished using an [[einzel lens]] energized at up to 600 volts.<ref>{{Cite patent |country=US |number=5382883A |url=https://patents.google.com/patent/US5382883A/en |title=Multi-beam group electron gun with common lens for color CRT}}</ref><ref name=Gassler2016>{{cite book |doi=10.1007/978-3-319-14346-0_70 |chapter=Cathode Ray Tubes (CRTS) |title=Handbook of Visual Display Technology |year=2016 |last1=Gassler |first1=Gerhard |pages=1595–1607 |publisher=Springer |location=Cham |isbn=978-3-319-14345-3 }}</ref> Before electrostatic focusing, focusing the electron beam required a large, heavy and complex mechanical focusing system placed outside the electron gun.<ref name="auto53"/>

However, electrostatic focusing cannot be accomplished near the final anode of the CRT due to its high voltage in the dozens of Kilovolts, so a high voltage (≈600–8000&nbsp;V)<ref>{{Cite web|url=http://bunkerofdoom.com/crt10sp4/index.html|title=Round CRT for Video or Computer|website=bunkerofdoom.com}}</ref> electrode, together with an electrode at the final anode voltage of the CRT, may be used for focusing instead. Such an arrangement is called a bipotential lens, which also offers higher performance than an einzel lens, or, focusing may be accomplished using a magnetic focusing coil together with a high anode voltage of dozens of kilovolts. However, magnetic focusing is expensive to implement, so it is rarely used in practice.<ref name="auto54"/><ref name=Gassler2016/><ref>{{Cite web|url=http://repairfaq.cis.upenn.edu/Misc/REPAIR/F_monfaqa.html#MONFAQA_019|title=Sci.Electronics.Repair FAQ: Notes on the Troubleshooting and Repair of Computer and Video Monitors|website=repairfaq.cis.upenn.edu|access-date=8 December 2020|archive-date=31 October 2020|archive-url=https://web.archive.org/web/20201031113759/http://repairfaq.cis.upenn.edu/Misc/REPAIR/F_monfaqa.html#MONFAQA_019|url-status=dead}}</ref><ref>{{Cite book|author= Thorn-AEI Radio Valves and Tubes Limited |url=http://www.r-type.org/articles/art-004f.htm |title=Electrons in Shadow-mask Colour Tubes|location= United Kingdom|date=1968}}</ref> Some CRTs may use two grids and lenses to focus the electron beam.<ref name="auto26"/> The focus voltage is generated in the flyback using a subset of the flyback's high voltage winding in conjunction with a resistive voltage divider. The focus electrode is connected alongside the other connections that are in the neck of the CRT.<ref>{{Cite web|url=http://repairfaq.cis.upenn.edu/samnew/tvfaq/tvfocdrift.htm|title=SER FAQ: TVFAQ: Focus drift with warmup|website=repairfaq.cis.upenn.edu|access-date=8 December 2020|archive-date=30 October 2020|archive-url=https://web.archive.org/web/20201030215231/http://repairfaq.cis.upenn.edu/samnew/tvfaq/tvfocdrift.htm|url-status=dead}}</ref>

There is a voltage called cutoff voltage which is the voltage that creates black on the screen since it causes the image on the screen created by the electron beam to disappear, the voltage is applied to G1. In a color CRT with three guns, the guns have different cutoff voltages. Many CRTs share grid G1 and G2 across all three guns, increasing image brightness and simplifying adjustment since on such CRTs there is a single cutoff voltage for all three guns (since G1 is shared across all guns).<ref name="auto6"/> but placing additional stress on the video amplifier used to feed video into the electron gun's cathodes, since the cutoff voltage becomes higher. Monochrome CRTs do not suffer from this problem. In monochrome CRTs video is fed to the gun by varying the voltage on the first control grid.<ref>{{Cite web|url=https://www.radartutorial.eu/12.scopes/sc16.en.html|title=Radartutorial|website=www.radartutorial.eu}}</ref><ref name="auto53"/>

During retracing of the electron beam, the preamplifier that feeds the video amplifier is disabled and the video amplifier is biased to a voltage higher than the cutoff voltage to prevent retrace lines from showing, or G1 can have a large negative voltage applied to it to prevent electrons from getting out of the cathode.<ref name="auto68"/> This is known as blanking. (see [[Vertical blanking interval]] and [[Horizontal blanking interval]].) Incorrect biasing can lead to visible retrace lines on one or more colors, creating retrace lines that are tinted or white (for example, tinted red if the red color is affected, tinted magenta if the red and blue colors are affected, and white if all colors are affected).<ref>{{Cite web|url=https://www.repairfaq.org/samnew/tvfaq/tvrgbrlin.htm|title=SER FAQ: TVFAQ: Red, green, or blue retrace lines|website=www.repairfaq.org}}</ref><ref>{{Cite web|url=https://www.repairfaq.org/samnew/tvfaq/tvwgrlin.htm|title=SER FAQ: TVFAQ: White/gray retrace lines|website=www.repairfaq.org}}</ref><ref name="auto32">{{cite web |url=https://www.ti.com/lit/an/snla017/snla017.pdf?ts=1599041272338&ref_url=https%253A%252F%252Fwww.google.com%252F |title= AN-656 Understanding the Operation of a CRT Monitor |website=www.ti.com |format=PDF|access-date=2020-12-11}}</ref> Alternatively, the amplifier may be driven by a video processor that also introduces an OSD (On Screen Display) into the video stream that is fed into the amplifier, using a fast blanking signal.<ref>{{cite web |url= https://www.st.com/resource/en/datasheet/CD00003613.pdf |archive-url=https://web.archive.org/web/20210227224753/https://www.st.com/resource/en/datasheet/CD00003613.pdf |archive-date=2021-02-27 |url-status=live|title=Data |website=www.st.com |access-date=2020-12-11}}</ref> TV sets and computer monitors that incorporate CRTs need a DC restoration circuit to provide a video signal to the CRT with a DC component, restoring the original brightness of different parts of the image.<ref>{{cite web |url=https://www.ti.com/lit/an/snla017/snla017.pdf |title=AN-656 Understanding the Operation of a CRT Monitor |website=www.ti.com |access-date=2020-12-11}}</ref>

The electron beam may be affected by the Earth's magnetic field, causing it to normally enter the focusing lens off-center; this can be corrected using astigmation controls. Astigmation controls are both magnetic and electronic (dynamic); magnetic does most of the work while electronic is used for fine adjustments.<ref>{{Cite web|url=http://www.curtpalme.com/Focus_and_Mechanical_Aim7.shtm|title=CRT Projector Focus & Mechanical Aim Basics by Guy Kuo|website=www.curtpalme.com}}</ref> One of the ends of the electron gun has a glass disk, the edges of which are fused with the edge of the neck of the CRT, possibly using [[frit]];<ref>{{Cite patent |country=US |number=6139388A |url=https://patents.google.com/patent/US6139388A/en |title=Method of forming a frit seal between a stem and a neck of a cathode ray tube during manufacturing of a cathode ray tube}}</ref> the metal leads that connect the electron gun to the outside pass through the disk.<ref>{{Cite patent |country=US |number=6677701B2 |url=https://patents.google.com/patent/US6677701B2/en |title=Stem for cathode ray tube}}</ref>

Some electron guns have a quadrupole lens with dynamic focus to alter the shape and adjust the focus of the electron beam, varying the focus voltage depending on the position of the electron beam to maintain image sharpness across the entire screen, specially at the corners.<ref name="auto4"/><ref>{{cite journal |last1=Bae |first1=Mincheol |last2=Song |first2=Yongseok |last3=Hong |first3=Younggon |last4=Kwon |first4=Yonggeol |last5=Lee |first5=Kwangsik |title=42.1: A New Electron Gun for a 32ʺ Super Wide Deflection Angle (120°) CRT |journal=SID Symposium Digest of Technical Papers |date=2001 |volume=32 |issue=1 |pages=1112 |doi=10.1889/1.1831753 |s2cid=110552592 }}</ref><ref name="auto61">{{cite thesis |last1=Sluijterman |first1=AAS Seyno |title=Innovative use of magnetic quadrupoles in cathode-ray tubes |date=2002 |doi=10.6100/IR555490 }}</ref><ref>{{Cite patent |country=US |number=4230972A |url=https://patents.google.com/patent/US4230972A/en |title=Dynamic focus circuitry for a CRT data display terminal}}</ref><ref>{{Cite web|url=http://repairfaq.cis.upenn.edu/Misc/REPAIR/F_monfaqb.html|title=Sci.Electronics.Repair FAQ: Notes on the Troubleshooting and Repair of Computer and Video Monitors|website=repairfaq.cis.upenn.edu|access-date=8 December 2020|archive-date=13 December 2020|archive-url=https://web.archive.org/web/20201213200911/http://repairfaq.cis.upenn.edu/Misc/REPAIR/F_monfaqb.html|url-status=dead}}</ref> They may also have a bleeder resistor to derive voltages for the grids from the final anode voltage.<ref>{{Cite web|url=http://www.lgphilips-displays.com:80/english/download/hdfolderdec2002.pdf|date=26 October 2005|archive-url=https://web.archive.org/web/20051026141832/http://www.lgphilips-displays.com/english/download/hdfolderdec2002.pdf|title=Data|archive-date=26 October 2005|access-date=6 February 2021|url-status=live}}</ref><ref>{{Cite patent |country=US |number=4682962A |url=https://patents.google.com/patent/US4682962A/en |title=Method of manufacturing a cathode ray tube}}</ref><ref>{{Cite patent |country=KR |number=830000491B1 |url=https://patents.google.com/patent/KR830000491B1/en |title=Partial voltage resistor of electron gun structure}}</ref>

After the CRTs were manufactured, they were aged to allow cathode emission to stabilize.<ref>{{Cite patent |country=US |number=4832646A |url=https://patents.google.com/patent/US4832646A/en |title=Aging process for cathode ray tubes}}</ref><ref>{{Cite patent |country=JP |number=2000082402A |url=https://patents.google.com/patent/JP2000082402A/en |title=Aging device for cathode-ray tube}}</ref>

The electron guns in color CRTs are driven by a video amplifier which takes a signal per color channel and amplifies it to 40–170&nbsp;V per channel, to be fed into the electron gun's cathodes;<ref name="auto32"/> each electron gun has its own channel (one per color) and all channels may be driven by the same amplifier, which internally has three separate channels.<ref>{{cite web |url=https://www.ti.com/lit/an/snoa268/snoa268.pdf |archive-url=https://web.archive.org/web/20201030080137/https://www.ti.com/lit/an/snoa268/snoa268.pdf |archive-date=2020-10-30 |url-status=live |title= AN-861 Guide to CRT Video Design |website= www.ti.com|access-date=2020-12-11}}</ref> The amplifier's capabilities limit the resolution, refresh rate and contrast ratio of the CRT, as the amplifier needs to provide high bandwidth and voltage variations at the same time; higher resolutions and refresh rates need higher bandwidths (speed at which voltage can be varied and thus switching between black and white) and higher contrast ratios need higher voltage variations or amplitude for lower black and higher white levels. 30&nbsp;MHz of bandwidth can usually provide 720p or 1080i resolution, while 20&nbsp;MHz usually provides around 600 (horizontal, from top to bottom) lines of resolution, for example.<ref name="auto92">{{Cite web|url=https://www.audioholics.com/hdtv-formats/display-technologies-guide-lcd-plasma-dlp-lcos-d-ila-crt/display-technologies-guide-lcd-plasma-dlp-lcos-d-ila-crt-page-7|title=Cathode Ray Tube (CRT) Direct View and Rear Projection TVs|first=Clint|last=DeBoer|website=Audioholics Home Theater, HDTV, Receivers, Speakers, Blu-ray Reviews and News|date=30 August 2004 }}</ref><ref name="auto32"/> The difference in voltage between the cathode and the control grid is what modulates the electron beam, modulating its current and thus creating shades of colors which create the image line by line and this can also affect the brightness of the image.<ref name="auto"/> The phosphors used in color CRTs produce different amounts of light for a given amount of energy, so to produce white on a color CRT, all three guns must output differing amounts of energy. The gun that outputs the most energy is the red gun since the red phosphor emits the least amount of light.<ref name="auto32"/>

====Gamma====
CRTs have a pronounced [[triode]] characteristic, which results in significant [[gamma correction|gamma]] (a nonlinear relationship in an electron gun between applied video voltage and beam intensity).<ref>{{cite web |url=http://broadcastengineering.com/newsrooms/broadcasting_gamma_correction/ |title=Gamma correction |access-date=4 October 2009 |last=Robin |first=Michael |date=1 January 2005 |work=BroadcastEngineering |url-status=dead |archive-url=https://web.archive.org/web/20090531130845/http://broadcastengineering.com/newsrooms/broadcasting_gamma_correction/ |archive-date=31 May 2009}}</ref>

===Deflection===
<!--split deflection yoke-->
There are two types of deflection: magnetic and electrostatic. Magnetic is usually used in TVs and monitors as it allows for higher deflection angles (and hence shallower CRTs) and deflection power (which allows for higher electron beam current and hence brighter images)<ref>{{cite web |url=http://sbe.org/handbook/fundamentals/Video/Video-Electron_Optics.pdf |title= Handbook|website= sbe.org|access-date=2020-12-11}}</ref> while avoiding the need for high voltages for deflection of up to 2&nbsp;kV,<ref name="auto45"/> while oscilloscopes often use electrostatic deflection since the raw waveforms captured by the oscilloscope can be applied directly (after amplification) to the vertical electrostatic deflection plates inside the CRT.<ref>{{cite book |doi=10.1016/b978-0-12-373865-3.00002-1 |chapter=Basic Instrumentation for Optical Measurement |title=Fiber Optic Measurement Techniques |year=2009 |last1=Hui |first1=Rongqing |last2=O'Sullivan |first2=Maurice |pages=129–258 |isbn=978-0-12-373865-3 }}</ref>

====Magnetic deflection====
{{Main|Magnetic deflection}}
Those that use magnetic deflection may use a yoke that has two pairs of deflection coils; one pair for vertical, and another for horizontal deflection.<ref name="auto44">{{Cite patent |country=US |number=6686709 |url=https://www.freepatentsonline.com/6686709.html |title=Deflection yoke for a CRT}}</ref> The yoke can be bonded (be integral) or removable. Those that were bonded used glue<ref name="auto58">{{Cite patent |country=US |number=6100779A |url=https://patents.google.com/patent/US6100779A/en |title=CRT deflection unit and its method of manufacture}}</ref> or a plastic<ref>{{Cite patent |country=US |number=4673906A |url=https://patents.google.com/patent/US4673906A/en |title=CRT deflection yoke with rigidifying means}}</ref> to bond the yoke to the area between the neck and the funnel of the CRT while those with removable yokes are clamped.<ref>{{Cite web|url=http://www.curtpalme.com/Yoke.shtm|title=CRT Projector Yoke Adjustments|website=www.curtpalme.com}}</ref><ref name="auto48"/> The yoke generates heat whose removal is essential since the conductivity of glass goes up with increasing temperature, the glass needs to be insulating for the CRT to remain usable as a capacitor. The temperature of the glass below the yoke is thus checked during the design of a new yoke.<ref name="auto63"/> The yoke contains the deflection and convergence coils with a ferrite core to reduce loss of magnetic force<ref>{{Cite patent |country=US |number=6686709B2 |url=https://patents.google.com/patent/US6686709B2/en |title=Deflection yoke for a CRT}}</ref><ref name="auto44"/> as well as the magnetized rings used to align or adjust the electron beams in color CRTs (The color purity and convergence rings, for example)<ref>{{Cite patent |country=US |number=7138755B2 |url=https://patents.google.com/patent/US7138755B2/en |title=Color picture tube apparatus having beam velocity modulation coils overlapping with convergence and purity unit and ring shaped ferrite core}}</ref> and monochrome CRTs.<ref>{{Cite patent |country=US |number=20010015612A1 |url=https://patents.google.com/patent/US20010015612A1/en|title=Deflection yoke}}</ref><ref name="auto19">{{cite web |url=https://deramp.com/downloads/sd_systems/Motorola%20MD3573%20Monitor.pdf |archive-url=https://web.archive.org/web/20190206104228/http://deramp.com/downloads/sd_systems/Motorola%20MD3573%20Monitor.pdf |archive-date=2019-02-06 |url-status=live |title=Service manual|website=deramp.com |access-date=2020-12-11}}</ref> The yoke may be connected using a connector, the order in which the deflection coils of the yoke are connected determines the orientation of the image displayed by the CRT.<ref name="auto15"/> The deflection coils may be held in place using polyurethane glue.<ref name="auto58"/>

The deflection coils are driven by sawtooth signals<ref>{{Cite patent |country=US |number=3725726A |url=https://patents.google.com/patent/US3725726A/en|title=Crt geometry correction with zero offset}}</ref><ref>{{Cite patent |country=US |number=6046538A |url=https://patents.google.com/patent/US6046538A/en |title=Deflection yoke and yoke core used for the deflection yoke}}</ref><ref name="auto32"/> that may be delivered through VGA as horizontal and vertical sync signals.<ref>{{cite web |url=http://lslwww.epfl.ch/pages/teaching/cours_lsl/ca_es/VGA.pdf |archive-url=https://web.archive.org/web/20031024072732/http://lslwww.epfl.ch/pages/teaching/cours_lsl/ca_es/VGA.pdf |archive-date=2003-10-24 |url-status=live |title=A VCA display courser |website=lslwww.epfl.ch |access-date=2020-12-11}}</ref> A CRT needs two deflection circuits: a horizontal and a vertical circuit, which are similar except that the horizontal circuit runs at a much higher frequency (a [[Horizontal scan rate]]) of 15–240&nbsp;kHz depending on the refresh rate of the CRT and the number of horizontal lines to be drawn (the vertical resolution of the CRT). The higher frequency makes it more susceptible to interference, so an automatic frequency control (AFC) circuit may be used to lock the phase of the horizontal deflection signal to that of a sync signal, to prevent the image from becoming distorted diagonally. The vertical frequency varies according to the refresh rate of the CRT. So a CRT with a 60&nbsp;Hz refresh rate has a vertical deflection circuit running at 60&nbsp;Hz. The horizontal and vertical deflection signals may be generated using two circuits that work differently; the horizontal deflection signal may be generated using a voltage controlled oscillator (VCO) while the vertical signal may be generated using a triggered relaxation oscillator. In many TVs, the frequencies at which the deflection coils run is in part determined by the inductance value of the coils.<ref>{{Cite web|url=https://www.repairfaq.org/samnew/tvfaq/tvdeflytst.htm|title=SER FAQ: TVFAQ: Deflection yoke testing|website=www.repairfaq.org}}</ref><ref name="auto32"/> CRTs had differing deflection angles; the higher the deflection angle, the shallower the CRT<ref>{{Cite web|url=http://www.vintagetvsets.com/predicta.htm|title=Predicta Picture Tubes|website=www.vintagetvsets.com}}</ref> for a given screen size, but at the cost of more deflection power and lower optical performance.<ref name="auto63"/><ref name="auto10">{{Cite web|url=http://www.r-type.org/timeline/time-124.htm|title=110 Degree Scanning Advert|website=www.r-type.org}}</ref>

Higher deflection power means more current<ref name="auto5">{{Cite web|url=https://phys.org/news/2005-03-stmicroelectronics-unveils-worlds-vertical-deflection.html|title=STMicroelectronics Unveils the World's First Vertical Deflection Booster for Slim CRT Displays|website=phys.org}}</ref> is sent to the deflection coils to bend the electron beam at a higher angle,<ref name="auto4"/> which in turn may generate more heat or require electronics that can handle the increased power.<ref name="auto10"/> Heat is generated due to resistive and core losses.<ref name="auto99">{{Cite patent |country=US |number=4737752A |url=https://patents.google.com/patent/US4737752A/en |title=Oscilloscope deflection yoke with heat dissipation means}}</ref> The deflection power is measured in mA per inch.<ref name="auto32"/> The vertical deflection coils may require ~24 volts while the horizontal deflection coils require ~120 volts to operate.

The deflection coils are driven by deflection amplifiers.<ref>{{Cite book|url=https://books.google.com/books?id=5wkXHE2NZO8C&q=15734Hz+crt&pg=PA287|title=The Technician's Radio Receiver Handbook: Wireless and Telecommunication Technology|isbn=9780080518596|last1=Carr|first1=Joseph|date=14 February 2001|publisher=Elsevier }}</ref> The horizontal deflection coils may also be driven in part by the horizontal output stage of a TV set. The stage contains a capacitor that is in series with the horizontal deflection coils that performs several functions, among them are: shaping the sawtooth deflection signal to match the curvature of the CRT and centering the image by preventing a DC bias from developing on the coil. At the beginning of retrace, the magnetic field of the coil collapses, causing the electron beam to return to the center of the screen, while at the same time the coil returns energy into capacitors, the energy of which is then used to force the electron beam to go to the left of the screen.<ref name="auto89"/>

Due to the high frequency at which the horizontal deflection coils operate, the energy in the deflection coils must be recycled to reduce heat dissipation. Recycling is done by transferring the energy in the deflection coils' magnetic field to a set of capacitors.<ref name="auto89">{{cite web |url=http://www.repairfaq.org/sam/reppic/horiz-tv.pdf |archive-url=https://web.archive.org/web/20040213034804/http://www.repairfaq.org/sam/reppic/horiz-tv.pdf |archive-date=2004-02-13 |url-status=live |title=Understanding The TV Horizontal Output Stage |website=www.repairfaq.org |access-date=2020-12-11}}</ref> The voltage on the horizontal deflection coils is negative when the electron beam is on the left side of the screen and positive when the electron beam is on the right side of the screen. The energy required for deflection is dependent on the energy of the electrons.<ref>{{Cite book|url=https://books.google.com/books?id=QtJ5tNdlyYAC&q=crt+deflection+coil&pg=PA157|title = Radio-Frequency Electronics: Circuits and Applications|isbn = 9780521553568|last1 = Hagen|first1 = Jon B.|date = 13 November 1996| publisher=Cambridge University Press }}</ref> Higher energy (voltage and/or current) electron beams need more energy to be deflected,<ref name="auto2"/> and are used to achieve higher image brightness.<ref>{{cite journal |url=https://link.springer.com/content/pdf/10.1007%2FBF03167599.pdf |archive-url=https://web.archive.org/web/20180724200714/https://link.springer.com/content/pdf/10.1007%2FBF03167599.pdf |archive-date=2018-07-24 |url-status=live |title=Data|journal=Journal of Digital Imaging |year=1990|doi=10.1007/BF03167599|pmid=2085547|access-date=2020-12-11|last1=Roehrig|first1=H.|last2=Blume|first2=H.|last3=Ji|first3=T. L.|last4=Browne|first4=M.|volume=3|issue=3|pages=134–45|s2cid=9805111}}</ref><ref>{{Cite patent |country=US |number=2457175 |url=https://www.freepatentsonline.com/2457175.html |title=Projection cathode-ray tube}}</ref><ref name="auto36"/>

====Electrostatic deflection====
{{Main|Electrostatic deflection}}
Mostly used in oscilloscopes. Deflection is carried out by applying a voltage across two pairs of plates, one for horizontal, and the other for vertical deflection. The electron beam is steered by varying the voltage difference across plates in a pair; For example, applying a voltage to the upper plate of the vertical deflection pair, while keeping the voltage in the bottom plate at 0 volts, will cause the electron beam to be deflected towards the upper part of the screen; increasing the voltage in the upper plate while keeping the bottom plate at 0 will cause the electron beam to be deflected to a higher point in the screen (will cause the beam to be deflected at a higher deflection angle). The same applies with the horizontal deflection plates. Increasing the length and proximity between plates in a pair can also increase the deflection angle.<ref>{{cite web | first=Kirt |last=Blattenberger | title=Navy Electricity and Electronics Training Series (NEETS), Module 16 | website=RF Cafe | url=https://www.rfcafe.com/references/electrical/NEETS-Modules/NEETS-Module-16-6-1-6-10.htm | access-date=2020-12-11}} <!--appears to be a US military source--></ref>

===Burn-in===
{{Further|Screen burn-in#CRT}}
Burn-in is when images are physically "burned" into the screen of the CRT; this occurs due to degradation of the phosphors due to prolonged electron bombardment of the phosphors, and happens when a fixed image or logo is left for too long on the screen, causing it to appear as a "ghost" image or, in severe cases, also when the CRT is off. To counter this, [[screensaver]]s were used in computers to minimize burn-in.<ref name="auto33">{{cite web | title=PERSONAL COMPUTERS; How To Avoid Burn-In | website=The New York Times | date=1991-04-02 | url=https://www.nytimes.com/1991/04/02/science/personal-computers-how-to-avoid-burn-in.html | access-date=2020-12-11}}</ref> Burn-in is not exclusive to CRTs, as it also happens to plasma displays and OLED displays.

===Evacuation===
The CRT's [[partial vacuum]] of {{Convert|0.01|Pa|atm|sigfig=1|adj=ri2}}<ref>[http://wps.aw.com/wps/media/objects/877/898586/topics/topic07.pdf Topic 7 |The Cathode-Ray Tube] {{Webarchive|url=https://web.archive.org/web/20171215132600/http://wps.aw.com/wps/media/objects/877/898586/topics/topic07.pdf|date=15 December 2017}}. aw.com. 2003-08-01<!--The interior of the tube is a very good vacuum, with a pressure of around 0.01 Pa (10^−7 atm) or less. At any greater pressure, collisions of electrons with air molecules would scatter the electron beam excessively.--></ref> to {{Convert|0.133|uPa|atm|sigfig=1|adj=ri1}} or less<ref>[http://www.repairfaq.org/sam/lasercva.htm repairfaq.org – Sam's Laser FAQ – Vacuum Technology for Home-Built Gas Lasers] {{Webarchive|url=https://web.archive.org/web/20121009185307/http://repairfaq.org/sam/lasercva.htm|date=9 October 2012}}. repairfaq.org. 2012-08-02<!--The actual vacuum inside the CRT of a computer monitor or TV is probably at 10^-9 Torr or better.--></ref> is evacuated or exhausted in a ~375–475&nbsp;°C [[oven]] in a process called ''baking'' or ''bake-out''.<ref>{{Cite patent |country=US |number=5405722A |url=https://patents.google.com/patent/US5405722A/en |title=Method for combined baking-out and sealing of an electrophotographically processed screen assembly for a cathode-ray tube}}</ref> The evacuation process also outgasses any materials inside the CRT, while decomposing others such as the polyvinyl alcohol used to apply the phosphors.<ref>{{Cite patent |country=US |number=4217015 |url=https://www.freepatentsonline.com/4217015.html |title=Cathode ray tube and a ventilator used in its baking process}}</ref> The heating and cooling are done gradually to avoid inducing stress, stiffening and possibly cracking the glass; the oven heats the gases inside the CRT, increasing the speed of the gas molecules which increases the chances of them getting drawn out by the vacuum pump. The temperature of the CRT is kept to below that of the oven, and the oven starts to cool just after the CRT reaches 400&nbsp;°C, or, the CRT was kept at a temperature higher than 400&nbsp;°C for up to 15–55 minutes. The CRT was heated during or after evacuation, and the heat may have been used simultaneously to melt the frit in the CRT, joining the screen and funnel.<ref>{{Cite patent |country=US |number=3922049A |url=https://patents.google.com/patent/US3922049A/en |title=Method of degassing a cathode-ray tube prior to sealing}}</ref><ref>{{Cite patent |country=US |number=2956374A |url=https://patents.google.com/patent/US2956374A/en |title=Glass bulb fabrication}}</ref><ref>{{Cite patent |country=CA |number=1229131A |url=https://patents.google.com/patent/CA1229131A/en |title=Method for combined baking-out and panel-sealing of a partially-assembled crt}}</ref> The pump used is a [[turbomolecular pump]] or a [[diffusion pump]].<ref>{{Cite patent |country=JP |number=H06349411A |url=https://patents.google.com/patent/JPH06349411A/en |title=Method for sealing-off cathode-ray tube}}</ref><ref>{{cite report |first1=M. J. |last1=Ozeroff |first2=W. A. |last2=Thornton |first3=J. R. |last3=Young |date=29 April 1953 |title=Proposed Improvement in Evacuation Technique for TV Tubes|url=http://www.one-electron.com/Archives/GE/GE_CRT_InternalMemos/GE%20Ozeroff%20et%20al%201953%20Proposed%20Improvement%20in%20Evacuation%20Technique%20for%20TV%20Tubes.pdf |archive-url=https://web.archive.org/web/20200215075217/http://www.one-electron.com/Archives/GE/GE_CRT_InternalMemos/GE%20Ozeroff%20et%20al%201953%20Proposed%20Improvement%20in%20Evacuation%20Technique%20for%20TV%20Tubes.pdf |archive-date=2020-02-15 |url-status=live }}</ref><ref>{{Cite web|url=http://www.earlytelevision.org/crt_workshop.html|title=CRT Rebuilding Workshop|website=www.earlytelevision.org}}</ref><ref>{{cite journal |last1=Goetz |first1=D. |last2=Schaefer |first2=G. |last3=Rufus |first3=J. |title=The use of turbomolecular pumps in television tube production |journal=Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films |date=4 June 1998 |volume=5 |issue=4 |pages=2421 |doi=10.1116/1.574467 }}</ref> Formerly mercury vacuum pumps were also used.<ref>{{Cite magazine|title=How television tubes are made<!--https://www.earlytelevision.org/pdf/Radio-News-1938-07_how_television_tubes_are_made.pdf-->|date=September 1938|magazine=Radio News}}</ref><ref>{{Cite web|url=http://www.earlytelevision.org/14ap4_construction.html|title=DuMont 14AP4|website=www.earlytelevision.org}}</ref> After baking, the CRT is disconnected ("sealed or tipped off") from the vacuum pump.<ref>{{cite patent |country=US |number=2787101 |url=https://patentimages.storage.googleapis.com/36/9e/db/7907793e2eb58b/US2787101.pdf <!-- |archive-url=https://web.archive.org/web/20201028224921/https://patentimages.storage.googleapis.com/36/9e/db/7907793e2eb58b/US2787101.pdf |archive-date=2020-10-28 |url-status=live --> |title=Picture-Tube Processing |pubdate= April 2, 1957|fdate=July 28, 1953}}</ref><ref>{{Cite web|url=https://patents.google.com/patent/US2871086A/en|title=Method for baking and exhausting electron discharge devices|accessdate=18 December 2022}}</ref><ref>{{Cite patent |country=US |number=4451725A |url=https://patents.google.com/patent/US4451725A/en |title=Electrical heating unit for sealing vacuum electron tubes}}</ref> The [[getter]] is then fired using an RF (induction) coil. The getter is usually in the funnel or in the neck of the CRT.<ref name="auto56">{{Cite web|url=https://www.earlytelevision.org/crt_rebuild.html|title=CRT Rebuilding|website=www.earlytelevision.org}}</ref><ref>{{Cite web|url=https://patents.google.com/patent/US3711734A/en|title=Cathode-ray tube having antenna getter with bimetallic insertion device|accessdate=18 December 2022}}</ref> The getter material which is often barium-based, catches any remaining gas particles as it evaporates due to heating induced by the RF coil (that may be combined with exothermic heating within the material); the vapor fills the CRT, trapping any gas molecules that it encounters and condenses on the inside of the CRT forming a layer that contains trapped gas molecules. [[Hydrogen]] may be present in the material to help distribute the barium vapor. The material is heated to temperatures above 1000&nbsp;°C, causing it to evaporate.<ref>{{Cite patent |country=US |number=20040104675A1 |url=https://patents.google.com/patent/US20040104675A1/en |title=Evaporable getter device for cathode-ray tubes}}</ref><ref>{{Cite patent |country=US |number=3121182A |url=https://patents.google.com/patent/US3121182A/en |title=Cathode ray tube, getter, and method of gettering}}</ref><ref name="ba">{{cite journal |last1=den Engelsen |first1=Daniel |last2=Ferrario |first2=Bruno |title=Gettering by Ba films in color cathode ray tubes |journal=Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena |date=1 March 2004 |volume=22 |issue=2 |pages=809–817 |doi=10.1116/1.1689973 |bibcode=2004JVSTB..22..809D }}</ref> Partial loss of vacuum in a CRT can result in a hazy image, blue glowing in the neck of the CRT, flashovers, loss of cathode emission or focusing problems.<ref name="auto53"/>

===Rebuilding===
CRTs used to be rebuilt; repaired or refurbished. The rebuilding process included the disassembly of the CRT, the disassembly and repair or replacement of the electron gun(s), the removal and redeposition of phosphors and [[aquadag]], etc. Rebuilding was popular until the 1960s because CRTs were expensive and wore out quickly, making repair worth it.<ref name="auto56"/> The last CRT rebuilder in the US closed in 2010,<ref>{{cite web | title=Last Lone Wolf CRT Rebuilder Closing | website=TV Technology | date=2010-07-06 | url=https://www.tvtechnology.com/news/last-lone-wolf-crt-rebuilder-closing | access-date=2020-12-11}}</ref> and the last in Europe, RACS, which was located in France, closed in 2013.<ref>{{cite web | title=CRT Rebuilding Project | website=Early Television Foundation | date=2015-01-02 | url=https://www.earlytelevision.org/crt_project.html | access-date=2020-12-11}}</ref>

===Reactivation===
Also known as rejuvenation, the goal is to temporarily restore the brightness of a worn CRT. This is often done by carefully increasing the voltage on the cathode heater and the current and voltage on the control grids of the electron gun manually.<ref>{{Cite web |title=CRT Restoration for the (Brave) Experimenter |url=http://www.ke5fx.com/crt.html |access-date=2025-03-06 |website=www.ke5fx.com}}</ref> Some rejuvenators can also fix heater-to-cathode shorts by running a capacitive discharge through the short.<ref name="auto"/>

===Phosphors===
[[Phosphor]]s in CRTs emit secondary electrons due to them being inside the vacuum of the CRT. The secondary electrons are collected by the anode of the CRT.<ref name="auto82"/> Secondary electrons generated by phosphors need to be collected to prevent charges from developing in the screen, which would lead to reduced image brightness<ref name="auto68"/> since the charge would repel the electron beam.

The phosphors used in CRTs often contain rare earth metals,<ref name="auto23">{{cite journal |last1=Yin |first1=Xiaofei |last2=Wu |first2=Yufeng |last3=Tian |first3=Xiangmiao |last4=Yu |first4=Jiamei |last5=Zhang |first5=Yi-Nan |last6=Zuo |first6=Tieyong |title=Green Recovery of Rare Earths from Waste Cathode Ray Tube Phosphors: Oxidative Leaching and Kinetic Aspects |journal=ACS Sustainable Chemistry & Engineering |date=5 December 2016 |volume=4 |issue=12 |pages=7080–7089 |doi=10.1021/acssuschemeng.6b01965 }}</ref><ref name="auto8">{{cite web |url=https://www.fh-muenster.de/ciw/downloads/personal/juestel/juestel/CRT-Phosphors.pdf |archive-url=https://web.archive.org/web/20201117063744/https://www.fh-muenster.de/ciw/downloads/personal/juestel/juestel/CRT-Phosphors.pdf |archive-date=2020-11-17 |url-status=live |title=Phosphors for Cathode-Ray Tubes |website=www.fh-muenster.de |access-date=2020-12-11}}</ref><ref name="auto33"/> replacing earlier dimmer phosphors. Early red and green phosphors contained Cadmium,<ref>{{Cite patent |country=US |number=4925593A |url=https://patents.google.com/patent/US4925593A/en |title=US4925593A - Method for producing cadmium free green emitting CRT phosphor}}</ref> and some black and white CRT phosphors also contained beryllium in the form of Zinc beryllium silicate,<ref name="auto93"/> although white phosphors containing cadmium, zinc and magnesium with silver, copper or manganese as dopants were also used.<ref name="auto68"/> The rare earth phosphors used in CRTs are more efficient (produce more light) than earlier phosphors.<ref>{{Cite patent |country=US |number=4035524A |url=https://patents.google.com/patent/US4035524A/en |title=Process for coating a phosphor slurry on the inner surface of a color cathode ray tube faceplate}}</ref> The phosphors adhere to the screen because of Van der Waals and electrostatic forces. Phosphors composed of smaller particles adhere more strongly to the screen. The phosphors together with the carbon used to prevent light bleeding (in color CRTs) can be easily removed by scratching.<ref name="Lee & Hsi 2002"/><ref>{{Cite book|url=https://books.google.com/books?id=Il7LBQAAQBAJ&q=phosphor+adhesion&pg=PA415|title = Phosphor Handbook|isbn = 9781420005233|last1 = Shionoya|first1 = Shigeo|last2 = Yen|first2 = William M.|last3 = Yamamoto|first3 = Hajime|date = 3 October 2018| publisher=CRC Press }}</ref>

Several dozen types of phosphors were available for CRTs.<ref>{{cite web |url=http://www.bunkerofdoom.com/tubes/crt/crt_phosphor_research.pdf |archive-url=https://web.archive.org/web/20130119132302/http://www.bunkerofdoom.com/tubes/crt/crt_phosphor_research.pdf |archive-date=2013-01-19 |url-status=live |title=Cathode Ray Tube Phosphor|website=www.bunkerofdoom.com|access-date=2020-12-11}}</ref> Phosphors were classified according to color, persistence, luminance rise and fall curves, color depending on anode voltage (for phosphors used in penetration CRTs), Intended use, chemical composition, safety, sensitivity to burn-in, and secondary emission properties.<ref name="auto64">{{Cite book|url=https://books.google.com/books?id=QazTBwAAQBAJ&q=crt+aluminized+screen&pg=PA240|title = Color in Electronic Displays|isbn = 9781475797541|last1 = Widdel|first1 = Heino|last2 = Post|first2 = David L.|date = 29 June 2013| publisher=Springer }}</ref> Examples of rare earth phosphors are [[yttrium]] oxide for red<ref>{{Cite web|url=https://patents.google.com/patent/US4151442A/en|title=Color television cathode ray tube}}</ref> and yttrium silicide for blue in beam index tubes,<ref>{{cite web
|url=https://www.labguysworld.com/crt_phosphor_research.pdf|title=Cathode Ray Tube Phosphors|website=labguysworld.com|access-date=27 March 2024}}</ref> while examples of earlier phosphors are copper cadmium sulfide for red,

SMPTE-C phosphors have properties defined by the SMPTE-C standard, which defines a color space of the same name. The standard prioritizes accurate color reproduction, which was made difficult by the different phosphors and color spaces used in the NTSC and PAL color systems. PAL TV sets have subjectively better color reproduction due to the use of saturated green phosphors, which have relatively long decay times that are tolerated in PAL since there is more time in PAL for phosphors to decay, due to its lower framerate. SMPTE-C phosphors were used in professional video monitors.<ref>{{cite web |url=https://www.cinemaquestinc.com/pdf/whitepaper.pdf |archive-url=https://web.archive.org/web/20160614153708/http://cinemaquestinc.com/pdf/whitepaper.pdf |archive-date=2016-06-14 |url-status=live |title= Implementing Display Standards in Modern Video Display Technologies |website=www.cinemaquestinc.com |access-date=2020-12-11}}</ref><ref>{{cite web |url=https://www.broadcaststore.com/pdf/model/20624/sonymonitorguide.pdf |archive-url=https://web.archive.org/web/20201214192909/https://www.broadcaststore.com/pdf/model/20624/sonymonitorguide.pdf |archive-date=2020-12-14 |url-status=live |title=Sony monitor guide |website= www.broadcaststore.com|access-date=2020-12-11}}</ref>

The phosphor coating on monochrome and color CRTs may have an aluminum coating on its rear side used to reflect light forward, provide protection against ions to prevent ion burn by negative ions on the phosphor, manage heat generated by electrons colliding against the phosphor,<ref name="auto28">{{Cite web|url=http://www.tuopeek.com/CRTs.html|title=Tuopeek: CRT Electron Guns|website=www.tuopeek.com}}</ref> prevent static build up that could repel electrons from the screen, form part of the anode and collect the secondary electrons generated by the phosphors in the screen after being hit by the electron beam, providing the electrons with a return path.<ref>{{cite web |url=https://www.circuitstoday.com/crt-cathode-ray-tube |title=CRT|website=www.circuitstoday.com|date=25 September 2009|access-date=2020-12-11}}
{{Cite patent |country=US |number=3893877A |url=https://patents.google.com/patent/US3893877A/en |title=Method and structure for metalizing a cathode ray tube screen}}</ref><ref name="auto63"/><ref>{{Cite web|url=https://www.thevalvepage.com/teletech/crt_manu/crt_manu.htm|title=Manufacture of C.R.T.'s|website=www.thevalvepage.com}}
{{cite web |url= https://frank.pocnet.net/sheets/201/1/12AGP7.pdf |archive-url=https://web.archive.org/web/20160909040652/http://frank.pocnet.net/sheets/201/1/12AGP7.pdf |archive-date=2016-09-09 |url-status=live|title=Rauland |website=frank.pocnet.net |access-date=2020-12-11}}</ref><ref name="auto28"/><ref name="auto68"/> The electron beam passes through the aluminum coating before hitting the phosphors on the screen; the aluminum attenuates the electron beam voltage by about 1&nbsp;kV.<ref name="auto31">{{Cite patent |country=US |number=4720655A |url=https://patents.google.com/patent/US4720655A/en |title=Flat color cathode-ray tube with phosphor index stripes}}</ref><ref name="auto68"/><ref name="auto64"/> A film or lacquer may be applied to the phosphors to reduce the surface roughness of the surface formed by the phosphors to allow the aluminum coating to have a uniform surface and prevent it from touching the glass of the screen.<ref>{{Cite patent |country=US |number=5800234 |url=https://patents.justia.com/patent/5800234|title=Method for manufacturing a metallized luminescent screen for a cathode-ray tube Patent |pubdate=1998-09-01}}</ref><ref name="auto80">{{Cite patent |country=US |number=5178906A |url=https://patents.google.com/patent/US5178906A/en |title=Method of manufacturing a phosphor screen for a CRT using an adhesion-promoting, blister-preventing solution}}</ref> This is known as filming.<ref name="auto52">{{cite web |url=http://www.one-electron.com/Archives/GE/GE_Cathode%20Ray%20Tube%20Dept%201958%20Syracuse%20Factory%20Brochure.pdf |archive-url=https://web.archive.org/web/20190828164614/http://www.one-electron.com/Archives/GE/GE_Cathode%20Ray%20Tube%20Dept%201958%20Syracuse%20Factory%20Brochure.pdf |archive-date=2019-08-28 |url-status=live |title=Cathode ray tube department |website=www.one-electron.com |access-date=2020-12-11}}</ref> The lacquer contains solvents that are later evaporated; the lacquer may be chemically roughened to cause an aluminum coating with holes to be created to allow the solvents to escape.<ref name="auto80"/>

====Phosphor persistence====
Various phosphors are available depending upon the needs of the measurement or display application. The brightness, color, and persistence of the illumination depends upon the type of phosphor used on the CRT screen. Phosphors are available with persistences ranging from less than one [[microsecond]] to several seconds.<ref>{{cite book |last= Doebelin |first= Ernest |title= Measurement Systems |publisher= McGraw Hill Professional |year= 2003 |page= 972 |url= https://books.google.com/books?id=q1mOopLHnTEC&pg=PA972 |isbn=978-0-07-292201-1}}</ref> For visual observation of brief transient events, a long persistence phosphor may be desirable. For events which are fast and repetitive, or high frequency, a short-persistence phosphor is generally preferable.<ref>{{cite book |last= Shionoya |first= Shigeo |title= Phosphor handbook |publisher= CRC Press |year= 1999 |page= 499 |url= https://books.google.com/books?id=lWlcJEDukRIC&pg=PA499 |isbn=978-0-8493-7560-6}}</ref> The phosphor persistence must be low enough to avoid smearing or ghosting artifacts at high refresh rates.<ref name="auto4"/>

===Limitations and workarounds===
====Blooming====
Variations in anode voltage can lead to variations in brightness in parts or all of the image, in addition to blooming, shrinkage or the image getting zoomed in or out. Lower voltages lead to blooming and zooming in, while higher voltages do the opposite.<ref>{{Cite web|url=https://www.repairfaq.org/samnew/tvfaq/tvexcesshv.htm|title=SER FAQ: TVFAQ: Excessive high voltage|website=www.repairfaq.org}}</ref><ref>{{Cite web|url=https://www.oldtellys.co.uk/otltbeht.html|title=line Timebase & EHT|website=www.oldtellys.co.uk}}</ref> Some blooming is unavoidable, which can be seen as bright areas of an image that expand, distorting or pushing aside surrounding darker areas of the same image. Blooming occurs because bright areas have a higher electron beam current from the electron gun, making the beam wider and harder to focus. Poor voltage regulation causes focus and anode voltage to go down with increasing electron beam current.<ref name="auto74"/>

====Doming====
Doming is a phenomenon found on some CRT TVs in which parts of the [[shadow mask]] become heated. In TVs that exhibit this behavior, it tends to occur in high-contrast scenes in which there is a largely dark scene with one or more localized bright spots.  As the electron beam hits the shadow mask in these areas it heats unevenly.  The shadow mask warps due to the heat differences, which causes the electron gun to hit the wrong colored phosphors and incorrect colors to be displayed in the affected area.<ref>{{Cite web|url=http://repairfaq.cis.upenn.edu/sam/crtfaq.htm#crtdom|title=TV and Monitor CRT (Picture Tube) Information|website=repairfaq.cis.upenn.edu|access-date=2020-12-21|archive-date=22 November 2020|archive-url=https://web.archive.org/web/20201122100132/http://repairfaq.cis.upenn.edu/sam/crtfaq.htm#crtdom|url-status=dead}}</ref> Thermal expansion causes the shadow mask to expand by around 100 microns.<ref>{{Cite patent |country=US |number=5079477A |url=https://patents.google.com/patent/US5079477A/en |title=Slot type shadow mask}}</ref><ref>{{Cite web|url=https://www.repairfaq.org/sam/tvfaq.htm|title=Notes on the Troubleshooting and Repair of Television Sets|website=www.repairfaq.org}}</ref><ref>{{Cite patent |country=US |number=5059874A |url=https://patents.google.com/patent/US5059874A/en |title=High voltage regulator for CRT display}}</ref><ref>{{Cite web|url=https://www.repairfaq.org/samnew/tvfaq/tvbloom.htm|title=SER FAQ: TVFAQ: Blooming or breathing problems|website=www.repairfaq.org}}</ref>

During normal operation, the shadow mask is heated to around 80–90&nbsp;°C.<ref name="auto78">{{Cite patent |country=US |number=5752755A |url=https://patents.google.com/patent/US5752755A/en |title=Method for making shadow mask for color picture tube and a shadow mask made thereby}}</ref> Bright areas of images heat the shadow mask more than dark areas, leading to uneven heating of the shadow mask and warping (blooming) due to thermal expansion caused by heating by increased electron beam current.<ref name="auto17">{{Cite book|url=https://books.google.com/books?id=-4ngT05gmAQC&q=shadow+mask+heat+warping&pg=PA160|title = Computer Graphics: Principles and Practice|isbn = 9780201848403|last1 = Foley|first1 = James D.|last2 = Van|first2 = Foley Dan|last3 = Dam|first3 = Andries Van|last4 = Feiner|first4 = Steven K.|last5 = Hughes|first5 = John F.|last6 = Angel|first6 = Edward|last7 = Hughes|first7 = J.|year = 1996| publisher=Addison-Wesley Professional }}</ref><ref>{{Cite patent |country=US |number=4339687A |url=https://patents.google.com/patent/US4339687A/en |title=Shadow mask having a layer of high atomic number material on gun side}}</ref> The shadow mask is usually made of steel but it can be made of [[Invar]]<ref name="auto85"/> (a low-thermal expansion Nickel-Iron alloy) as it withstands two to three times more current than conventional masks without noticeable warping,<ref name="auto4"/><ref>{{Cite patent |country=US |number=20040000857A1 |url=https://patents.google.com/patent/US20040000857A1/en |title=Warp-free dual compliant tension mask frame}}</ref><ref name="auto84"/> while making higher resolution CRTs easier to achieve.<ref name="auto97">{{Cite book|url=https://books.google.com/books?id=xRrtCAAAQBAJ&q=crt+shadow+mask+metal&pg=PA47|title = The Dynamics of the Computer Industry: Modeling the Supply of Workstations and their Components|isbn = 9789401121989|last1 = Touma|first1 = Walid Rachid|date = 6 December 2012| publisher=Springer }}</ref> Coatings that dissipate heat may be applied on the shadow mask to limit blooming<ref>{{Cite patent |country=KR |number=890003989B1 |url=https://patents.google.com/patent/KR890003989B1/en |title=Shadow mask for color cathode ray tube}}</ref><ref>{{Cite patent |country=US |number=3887828A |url=https://patents.google.com/patent/US3887828A/en|title=Shadow mask having conductive layer in poor thermal contact with mask}}</ref> in a process called blackening.<ref>{{Cite patent |country= |number= |url=https://patentscope.wipo.int/search/en/detail.jsf?docId=WO1990010946 |title=Blackening of Ni-Based Ftm Shadow Masks}}</ref><ref>{{Cite patent |country=US |number=4885501A |url=https://patents.google.com/patent/US4885501A/en |title=Blackening of non iron-based flat tensioned foil shadow masks}}</ref>

Bimetal springs may be used in CRTs used in TVs to compensate for warping that occurs as the electron beam heats the shadow mask, causing thermal expansion.<ref name="auto106"/> The shadow mask is installed to the screen using metal pieces<ref>{{Cite web|url=https://patents.google.com/patent/US6130501A/en|title=Shadow mask mounting arrangement for color CRT|accessdate=18 December 2022}}</ref> or a rail or frame<ref name="auto13">{{Cite web|url=https://patents.google.com/patent/US6628058B2/en|title=Flat tension mask type cathode ray tube|accessdate=18 December 2022}}</ref><ref>{{Cite web|url=https://patents.google.com/patent/JP2005524944A/en|title=Cathode ray tube with bracket for mounting a shadow mask frame|accessdate=18 December 2022}}</ref><ref>{{Cite web|url=https://patents.google.com/patent/US5982085A/en|title=Color cathode ray tube with improved shadow mask mounting system|accessdate=18 December 2022}}</ref> that is fused to the funnel or the screen glass respectively,<ref name="auto61"/> holding the shadow mask in tension to minimize warping (if the mask is flat, used in flat-screen CRT computer monitors) and allowing for higher image brightness and contrast.

Aperture grille screens are brighter since they allow more electrons through, but they require support wires. They are also more resistant to warping.<ref name="auto4"/> Color CRTs need higher anode voltages than monochrome CRTs to achieve the same brightness since the shadow mask blocks most of the electron beam. Slot masks<ref name="auto40"/> and specially Aperture grilles do not block as many electrons resulting in a brighter image for a given anode voltage, but aperture grille CRTs are heavier.<ref name="auto85"/> Shadow masks block<ref name="auto66">{{Cite web|url=https://patents.google.com/patent/US5509842A/en|title=Method for pre-stressing CRT tension mask material|accessdate=18 December 2022}}</ref> 80–85%<ref name="auto17"/><ref name="auto78"/> of the electron beam while Aperture grilles allow more electrons to pass through.<ref>{{Cite book|url=https://books.google.com/books?id=Cnj_3fFfPdsC&q=aperture+grille+blocks&pg=PA121|title = Maximum PC Guide to Building a Dream PC|isbn = 9780789731937|last1 = Smith|first1 = Will|year = 2004| publisher=Que }}</ref>

====High voltage====
Image brightness is related to the anode voltage and to the CRTs size, so higher voltages are needed for both larger screens<ref>{{cite web | title=US4929209A - Method of aging cathode-ray tube | website=Google Patents | date=1988-07-28 | url=https://patents.google.com/patent/US4929209 | access-date=2020-12-11}}</ref> and higher image brightness. Image brightness is also controlled by the current of the electron beam.<ref name="auto25"/> Higher anode voltages and electron beam currents also mean higher amounts of x-rays and heat generation since the electrons have a higher speed and energy.<ref name="auto74"/> Leaded glass and special barium-strontium glass are used to block most x-ray emissions.

====Size====
[[File:Top of Sony PVM-4300 (KX-45ED1) with cat.jpg|alt=Top view of Sony PVM-4300 with calico cat for scale|thumb|Top view of [[Sony PVM-4300]] with calico cat for scale]]
A practical limit on the size of a CRT is the weight of the thick glass needed to safely sustain its vacuum,<ref>{{Cite web|url=https://www.repairfaq.org/samnew/tvfaq/tvaffpv.htm|title=SER FAQ: TVFAQ: Arcing from flyback or vicinity|website=www.repairfaq.org}}</ref> since a CRT's exterior is exposed to the full atmospheric [[pressure]], which for instance totals {{Convert|5800|lbf|N|lk=on}} on a 27-inch (400&nbsp;[[Square inch|in<sup>2</sup>]]) screen.<ref>{{Cite patent|country=US|number=2874017A|title=Prevention of fracture in glass cathode-ray tubes|url=https://patents.google.com/patent/US2874017A/en}}</ref> For example, the large 43-inch [[Sony PVM-4300]] weighs {{Convert|440|lb|kg|lk=on|abbr=on|disp=or}},<ref>{{Cite web|url=https://www.theverge.com/2018/2/6/16973914/tvs-crt-restoration-led-gaming-vintage|title=Inside the desperate fight to keep old TVs alive|first=Adi|last=Robertson|date=February 6, 2018|website=The Verge}}</ref> much heavier than 32-inch CRTs (up to {{convert|163|lb|kg|abbr=on|disp=or}}) and 19-inch CRTs (up to {{convert|60|lb|kg|abbr=on|disp=or}}). Much lighter flat panel TVs are only ~{{convert|18|lb|kg|abbr=on}} for 32-inch and {{convert|6.5|lb|kg|abbr=on}} for 19-inch.<ref>{{cite web |url=https://www.cpsc.gov/s3fs-public/pdfs/TV-hazard-report-January2015.pdf |archive-url=https://web.archive.org/web/20170125124729/https://www.cpsc.gov/s3fs-public/pdfs/TV-hazard-report-January2015.pdf |archive-date=2017-01-25 |url-status=live |title= TVS -Tipping the Scale to Safety |date=2015 |website=www.cpsc.gov |access-date=2020-12-11}}</ref>

Size is also limited by anode voltage, as it would require a higher dielectric strength to prevent [[arcing]] and the electrical losses and ozone generation it causes, without sacrificing image brightness.

Shadow masks also become more difficult to make with increasing resolution and size.<ref name="auto97" />

====Limits imposed by deflection====
At high deflection angles, resolutions and refresh rates (since higher resolutions and refresh rates require significantly higher frequencies to be applied to the horizontal deflection coils), the deflection yoke starts to produce large amounts of heat, due to the need to move the electron beam at a higher angle, which in turn requires exponentially larger amounts of power. As an example, to increase the deflection angle from 90 to 120°, power consumption of the yoke must also go up from 40 watts to 80 watts, and to increase it further from 120 to 150°, deflection power must again go up from 80 to 160 [[watt]]s. This normally makes CRTs that go beyond certain deflection angles, resolutions and refresh rates impractical, since the coils would generate too much heat due to resistance caused by the [[skin effect]], surface and [[eddy current]] losses, and/or possibly causing the glass underneath the coil to become conductive (as the electrical conductivity of glass increases with increasing temperature).{{cn|date=December 2024}} Some deflection yokes are designed to dissipate the heat that comes from their operation.<ref name="auto38"/><ref>{{cite thesis |last1=Harberts |first1=D. W. |title=Dissipation and ringing of CRT deflection coils |date=2001 |url=https://research.tue.nl/en/publications/dissipation-and-ringing-of-crt-deflection-coils }}</ref><ref name="auto99"/><ref>{{Cite web|url=https://www.freepatentsonline.com/5204649.html|title=Deflection yoke|accessdate=18 December 2022}}</ref><ref>{{Cite web|url=https://patents.google.com/patent/US6650040B2/en|title=Cathode ray tube having a deflection yoke with heat radiator|accessdate=18 December 2022}}</ref><ref>{{cite journal |last1=Masuda |first1=Y. |last2=Akiyama |first2=T. |last3=Kitaoka |first3=M. |last4=Otobe |first4=S. |last5=Takei |first5=H. |last6=Kitaoka |first6=M. |title=23.2: Development of New Ferrite Material for Deflection Yoke Core |journal=SID Symposium Digest of Technical Papers |date=1998 |volume=29 |issue=1 |pages=343 |doi=10.1889/1.1833763 |s2cid=137042132 }}</ref> Higher deflection angles in color CRTs directly affect convergence at the corners of the screen which requires additional compensation circuitry to handle electron beam power and shape, leading to higher costs and power consumption.<ref>{{Cite web|url=https://www.extremetech.com/electronics/53826-crt-innovations/3|title=CRT Innovations - Page 3 of 7 - ExtremeTech|website=www.extremetech.com|access-date=8 December 2020|archive-date=8 October 2020|archive-url=https://web.archive.org/web/20201008230709/https://www.extremetech.com/electronics/53826-crt-innovations/3|url-status=dead}}</ref><ref>{{Cite web|url=https://www.latimes.com/archives/la-xpm-2005-sep-14-fi-tubes14-story.html|title=Samsung Refusing to Pull Plug on CRT Televisions|first1=Elliot|last1=Spagat|date=September 14, 2005|website=Los Angeles Times}}</ref> Higher deflection angles allow a CRT of a given size to be slimmer, however they also impose more stress on the CRT envelope, specially on the panel, the seal between the panel and funnel and on the funnel. The funnel needs to be long enough to minimize stress, as a longer funnel can be better shaped to have lower stress.<ref name="auto34"/><ref>{{cite web |url=https://www.koreascience.or.kr/article/CFKO200524282635548.pdf |archive-url=https://web.archive.org/web/20210706120621/https://www.koreascience.or.kr/article/CFKO200524282635548.pdf |archive-date=2021-07-06 |url-status=live |title= The Design of Glass for Vixlim |website=www.koreascience.or.kr |access-date=2020-12-11}}</ref>