Biggest oscilloscope tube - Page 1
Forum section: electronics / testgear

author: lukaszsmola
author_rank: Newbie
timestamp: April 25, 2023, 09:19:30 am
content: Hi everyoneI was wondering, what is the biggest oscilloscope cathode ray tube that you know of? Not length wise, I am wondering what is the largest display area that was achievable?

author: Fungus
author_rank: Super Contributor
timestamp: April 25, 2023, 09:38:06 am
content: Quote from: lukaszsmola on April 25, 2023, 09:19:30 amLength and screen size are physically related. You can't make large, short tubes so the device depth will always be the limiting factor - it has to fit on a bench.

author: nctnico
author_rank: Super Contributor
timestamp: April 25, 2023, 09:42:19 am
content: Quote from: Fungus on April 25, 2023, 09:38:06 amBig CRT TVs where pretty flat in relation to screen size so that reasoning doesn't fly.

author: wasedadoc
author_rank: Super Contributor
timestamp: April 25, 2023, 09:44:11 am
content: What about those big round radar displays you see in movies. But are they electrostatic deflection like 'scope CRTs or electromagnetic deflection like TV CRTs?

author: nali
author_rank: Frequent Contributor
timestamp: April 25, 2023, 09:59:27 am
content: Quote from: Fungus on April 25, 2023, 09:38:06 amHa... not everyone thinks like that. Some of the oldies here may remember these ->Source:https://en.wikipedia.org/wiki/TV80

author: tautech
author_rank: Super Contributor
timestamp: April 25, 2023, 10:45:29 am
content: Largest in a proper CRO I've seen was ~5" in a Telequipment D83, my first scope.At time of production they were a UK division of Tek and used Tek's T7400-31-2 CRT also used in their 7603 I believe.Green P31 trace behind blue filter was as bright, crisp and clear as anything you ever saw.

author: lukaszsmola
author_rank: Newbie
timestamp: April 25, 2023, 10:58:27 am
content: Quote from: Fungus on April 25, 2023, 09:38:06 amI understand that, just wanted to people that answer to focus only on the display size, sorry if I didn't make myself clear.

author: Grandchuck
author_rank: Super Contributor
timestamp: April 25, 2023, 11:07:35 am
content: School lab demo unit:https://www.ebay.com/itm/403824552356?var=0&mkevt=1&mkcid=1&mkrid=711-53200-19255-0&campid=5338767613&toolid=20006&customid=4581596248650289_377867555Years ago, there were some other demo scopes with even larger screens for showing waveforms to an audience.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 25, 2023, 12:26:37 pm
content: Many used for gas engine diagnostics had 21" or larger displays. Based on standard TV CRTs, and worked because of the limited bandwidth required.Here is one examplehttps://www.coastmachinery.com/product/sun-engine-analyzer-685-4/

author: tautech
author_rank: Super Contributor
timestamp: April 25, 2023, 12:34:23 pm
content: Quote from: CatalinaWOW on April 25, 2023, 12:26:37 pmLow BW might have been a better description in fact that low the earliest scopes were much much faster.Consider any modern chainsaw is operating at 10k+ RPM which is a very leisurely 166Hz and for the normal ICE few do over 100Hz which compared to decades old electronics is positively pedestrian.Okay these are ignitions scopes however nowhere in the same class as a proper electronics scope.

author: Gyro
author_rank: Super Contributor
timestamp: April 25, 2023, 01:06:15 pm
content: I don't know if big old circular radar tubes were electrostatic deflection (my personal definition of scope tube) or magnetic. They were a fair diameter though.

author: Fungus
author_rank: Super Contributor
timestamp: April 25, 2023, 01:51:03 pm
content: Quote from: nctnico on April 25, 2023, 09:42:19 amYou're the first person I've ever heard describe a CRT as "flat". I don't believe there was ever one that was less deep than is was wide.We weren't talking about TVs though. TVs are much slower scanning than oscilloscopes so they have more time to deflect the beam.More time = bigger deflection angle than a 'scope.Quote from: nali on April 25, 2023, 09:59:27 amI remember those.I also remember these:rear projection TV

author: bdunham7
author_rank: Super Contributor
timestamp: April 25, 2023, 02:04:41 pm
content: Quote from: Fungus on April 25, 2023, 01:51:03 pmAs mentioned, some scope applications are lower BW and television CRTs will display a BW of several MHz. They're still oscilloscopes.Later model large CRT televisions had pretty short tubes. The trick was being able to deal electronically with the geometry issues.https://hexus.net/ce/news/audio-visual/4947-samsung-unveils-hdtv-compatible-crt/

author: Wrenches of Death
author_rank: Regular Contributor
timestamp: April 25, 2023, 02:40:42 pm
content: Quote from: bdunham7 on April 25, 2023, 02:04:41 pmDeflection method was the primary reason. Electrostatic deflection required a long/deep crt. Magnetic deflection, using a yoke, could function with a much, much shorter neck.WoD

author: edavid
author_rank: Super Contributor
timestamp: April 25, 2023, 02:41:57 pm
content: I don't see the point of including magnetic deflection tubes, because obviously they can be very large.This isn't a complete oscilloscope, but the largest electrostatic deflection CRT I know of was the HP 1321A 21" XYZ monitor.I haven't seen that one in person, but I do have its smaller brother, the HP 1311A 14" 5MHz XYZ monitor. It's pretty impressive.

author: Wrenches of Death
author_rank: Regular Contributor
timestamp: April 25, 2023, 02:45:06 pm
content: Quote from: edavid on April 25, 2023, 02:41:57 pmI've never seen an electrostatic type CRT that large. How deep was it?thanks!WoD

author: edavid
author_rank: Super Contributor
timestamp: April 25, 2023, 02:49:49 pm
content: Quote from: Wrenches of Death on April 25, 2023, 02:45:06 pmThe cabinet was 25" deep. It only has 5MHz bandwidth so it could have a fairly wide deflection angle.

author: N2IXK
author_rank: Frequent Contributor
timestamp: April 25, 2023, 03:00:41 pm
content: DuMont made a small number of classroom demonstrator scopes with a 20" electrostatic CRT. They used a green phosphor (P1) version of their 20AP4 television CRT:https://www.earlytelevision.org/images/dumont_20ap4.jpg

author: alm
author_rank: Super Contributor
timestamp: April 25, 2023, 03:08:22 pm
content: If anything, the deeper the tube and the smaller the surface (small deflection angle), the higher the bandwidth. Seethis description of a 13 GHz scan convertor CRTwhich was over 3 meters deep. So a CRT with big surface area would make for a low bandwidth scope.