What is this? - Page 1
Forum section: electronics / beginners

author: Halvmand
author_rank: Regular Contributor
timestamp: November 04, 2016, 04:25:47 pm
content: My friends father has gotten a hold of some glassware, maybe meant for some electronics teaching or for demo purposes.Anyone that know what they are used for?He has ben smart enough to hook them up to one of them spheres with electrical arcs that spurs out to your finger when you touch them.When he does that, the bulbs light a faint violet.

author: Andy Watson
author_rank: Super Contributor
timestamp: November 04, 2016, 04:32:09 pm
content: Physics, electron demonstration apparatus. They look like variations on the Crookes tube.https://en.wikipedia.org/wiki/Crookes_tube

author: Halvmand
author_rank: Regular Contributor
timestamp: November 04, 2016, 04:56:28 pm
content: Thanks for the quick reply. The one on the wiki link looks exactly like one of the kinds he has.Has anyone used these in school at some point?

author: NottheDan
author_rank: Frequent Contributor
timestamp: November 04, 2016, 06:52:50 pm
content: Not used but the were brought out for demonstrations, running on top of an induction coil IIRC. The physics teacher didn't like to move them about because they were rather fragile and the wires to the metal caps were prone to breaking. I think the majority of the ones the school had were non-functional by my time.

author: ceoxrad
author_rank: Regular Contributor
timestamp: November 04, 2016, 07:19:35 pm
content: There is quite something here..I'll try to do my best, forgive any mistake pleasefrom right to left:1) a classical Crookes tube with the cross of Malta it's commonly used in physics lessons.2)the tube with the phosphor inside is meant to be used with a magnet, to show the deflection of an electron beam.3)the central one is not very well focused in the picture, it MIGHT be an xray tube.4)the little one at bottom left is definetly an old school cold cathode X-ray tube..if you have access to an high voltage PS and an intensifier screen you can try some interesting things with it..be aware that cold cathode x ray tubes have a lot of limitations. They are quite unstable, need a very high voltage to start conducting and they overheat quickly if the current is high (they are best used with a ruhmkorff coil)5)I'm not sure, sorry.

author: Gyro
author_rank: Super Contributor
timestamp: November 04, 2016, 07:20:00 pm
content: As the proud owner of an old Maltese cross and a Paddle wheel tube I can attest to the beauty of these things. They also have significant value these days.The glow in the tubes is produce both by florescence the soda glass (green) and the remaining gas molecules in the tube violet. They need some gas molecules to work as they are cold cathode.Just going around your photo...Top left is an Anode ray tube (actually positively charged ions in the less than perfect vacuum).Bottom left is an X-ray tube (cold cathode, Rontgen type).Center is a tube that demonstrates the heating effect of an electron beam (on the suspended foil target), it looks as if it's seen some use! Top right is a magnetic deflection tube, the white florescent screen shows the bending of the electrons' path when a magnet is held near it (there were also similar tubes with electostatic deflection plates.Finally, bottom right is the Maltese cross tube, the cross is hinged, when up it shows a shadow as electrons are stopped by the cross (proving that they move in straight lines). When down, the previously shadowed portion of the end of the tube. The glow is produced by bombardment of the glass by the electron beam (well, unfocussed stream). The shadowed area doesn't get as much exposure so glows brighter when it is exposed.A few cautions:- The tubes are evacuated (as near as makes no difference) and thin individually hand-blown glass (not like mass produced CRTs). One of mine has a section of fingerprint in the glass (ouch!) and the other, a bubble in the glass. If you knock them against each other, a hard object, or stress them, they WILL implode with fast moving shards of glass flying in all directions.- They are only intended for minimal current, they would have been driven by an induction coil, I drive mine at no more than 5kV with a current limit resistor to limit to a few hundred uA max. Too much current and you will overheat the electrodes.- All of the tubes are capable of generating X-rays to some extent if driven at too high a voltage - particularly the X-ray tube (obviously). They produce soft X-rays many of which are absorbed by flesh rather than passing through.In terms of age, they are notoriously difficult to age but looking at the detail and stands, some of them could be 1920s. They are still manufactured to this day in Germany.A really nice collection! I wish I could complete mine. Handle with care!P.S.Oops, some duplication with ceoxrad's and NottheDan's replies while typing.