0
\$\begingroup\$

Online, I could find that high-quality cathode-ray-tube displays (whether be it for a computer monitor or a television set) have a design lifespan of 30,000-50,000 hours of cumulative operation. I could also find that the design lifespan is limited to that because the physics of the operating mechanism with the material used for the electron gun dictates that. Because the material used is already the most-durable that can emit electrons, that makes it a fundamental limit to electron guns using thermionic emission. Thermionic emission is a sacrificial process in which the removal of electrons causes the atomic nuclei to become ionized, thereby ejecting from the filament, thereby causing the atoms overall to sputter from the electron gun. So, is it even possible for a picture tube to last 100,000 hours without a complete rebuild if terrible picture quality is ignored, or will the thermionic electron gun completely fail (stop emitting electrons entirely from being an open circuit) well before then?

However, I could not find any pictures of CRT displays that are just even claimed to have over 30,000 hours of runtime, let alone 50,000 or even 100,000. Here, I am referring to the picture tube only, not the driver that runs the CRT.

So, how does a CRT display that has over 30,000 hours of runtime look like, especially the screen burn-in when turned off? Also, how much are the individual colours faded when turned on at factory settings? I would most like to know that information for one with at least 100,000 hours of runtime. Please post photos and state the estimated number of hours, preferably with the uncertainty error bars too.

I would also like to know how one with 300,000 hours of operation is like, if it can even last that long without maintenance. 300,000 hours may sound crazy, but that is not for industrial equipment or for constant indicator lights on any equipment. For reference, 300,000 hours when always on is 34.224 years. For example, there are numerous examples of equipment using a non-sacrificial operating method, such as structural components, electrical transformers, and light-emitting-diode indicator lights, lasting over 35 years while being on 24/7 (structural components obviously are always functioning when assembled, so they cannot be turned off) without servicing of those components.

\$\endgroup\$
7
  • 2
    \$\begingroup\$ could you cite a source for your 50,000 hours? Because that's only 5.7 years of operation, and I'm very sure I saw CRT TVs that served a factor of 4 or 5 of that. \$\endgroup\$ Aug 6, 2023 at 12:14
  • 2
    \$\begingroup\$ But yes, you get burn-in. I'm sure someone has collected some data on how that progresses; I bet you can find a few good examples for that in train station departure displays, plant control rooms… \$\endgroup\$ Aug 6, 2023 at 12:18
  • 1
    \$\begingroup\$ AFAIUI, there are at least two major mechanisms- emission reduction from the cathode and phosphor damage primarily due to ion bombardment. Both those things improved drastically over the life cycle of CRTs as a viable component. CRT displays, for example, were (and still are) used in aircraft cockpits where an MTFB of 18,000 hours is quoted (DU-870). Most CRT datasheets contain no information at all on lifetime so you'll be lucky to find 1/10 of what you are requesting (eg. error bars) for even one type of CRT. \$\endgroup\$ Aug 6, 2023 at 13:45
  • \$\begingroup\$ @SpehroPefhany you raise an interesting point: a CRT used for say, professional photography postprocessing and a CRT used for say, monochrome "lineart" displays in a cockpit might have different requirements when it comes to uniformity, sharpness, alignment, absolute brightness, so that one would have to first define some hard requirements on what it means for a screen to fail before talking about lifetime. \$\endgroup\$ Aug 6, 2023 at 14:21
  • 1
    \$\begingroup\$ "I would most like to know that information for one with at least 100,000 hours of runtime." - why? \$\endgroup\$ Aug 6, 2023 at 21:29

1 Answer 1

1
\$\begingroup\$

I can't speak for phosphors, but cathodes can be made quite reliable.

Until the 1980s or so, transatlantic telephone cables were in use, using repeaters based on vacuum tubes. These amplifiers had reasonable bandwidth (low MHz), high linearity, and extremely long life: hundreds of millions of tube-hours across the couple thousand tubes used in these lines over their history, with zero, or very nearly zero, failures.

Bell System Technical Journal, 43: 4. July 1964 pp 1311-1338. Electron Tubes for the SD Submarine Cable System. (Holdaway, V.L.; Van Haste, W. ; Walsh, E.J.) contains a lot of information on the design and construction of the tubes used at that time. Related articles in that edition discuss the circuit, power distribution, mechanical design, etc. (I seem to recall a later (retrospective?) article including somewhat later history, but I can't seem to find it.)

Vacuum tubes aren't very important these days, save for a few highly enduring applications. Likely more information can be found in relation to traveling wave tubes for satellite (aerospace) service, or perhaps klystrons for radar and physics applications. (Or perhaps not, maybe high-reliability cathodes are becoming be more of a trade secret these days; I don't know.)

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.