[SOLVED] wanna disassemble old tv for its electron gun

[lynx_phoenix]

i've got a real old tv that doesn't work according to the people who gave it to me. i've already opened the dinosaur up and most of its pretty musty in there, loads of dust and stuff. what i'm interested in is the electron gun (without the screen), the power supply and perhaps anything else that might be interesting and useful, but not the old pcbs ofcourse. on these i have a few questions.

i've checked online and it seems there is a health hazard with the phosphor and some other chemical used for the screen i think. considering there is a vacuum on the inside of the screen, would separating the gun from the screen end up spreading the hazardous stuff all around my room, since air would rush in and unsettle it? is there a way to do this safely, if at all? the gun is stuck pretty tight to the funnel (looks like its glued there) and i'm not sure i can figure out how its supposed to come off. is there a 'usual way' to do it, or should i just try to pull it off with brute force?

also, the power supply seems to be screwed and welded onto the thing so i might forget about that, but is there anything else that is unique to these old tvs that might be of interest? i'm just scavenging for parts really.

thanks

 

[klystron]

Yes, it is dangerous to break a TV tube. The risk of hurting yourself (and people near you) is possibly more than the "value" of the electron gun
What do you want to do with the "electron gun"

 

[FvM]

You know, that an electron gun could be only used in a high vacuum? It's not very difficult to dismantle it from a TV CRT, but you also need a vaccum container with an electrical feed-through, and a high vacuum pump to operate it.

Possible implosion is the most serious safety risk when handling CRTs. As far as I remember, most CRTs have a pumping nozzle under the socket, that can be cut to vent them safely.

 

[betwixt]

Cutting the evacuation pip can still pop the tube. The method used commercially when the tube is having a new gun fitted but retaining the existing phosphor is to drill a tiny hole (< 1mm) into the neck, as close to the pins as possible. A normal drill will not work on glass you need one that grinds rather than cuts the glass. Not joking, a good source of these is a dentist, when they start to wear, the dentist will replace them but they will still cut glass and ceramic many more times.

Removing the neck is normally done by scoring a ring around it then tapping it gently, it will snap at the ring and come away intact.

Brian.

 

[lynx_phoenix]

@klystron - just wanted to scavenge it for later, i have no intention of using it at the moment. when you say "risk" is it risk due to implosion or chemicals? i'm asking because implosion i can handle with precautions but if toxic chemicals from inside the screen become airborne, since i'm at home, i'd rather avoid the operation entirely.

@FvM - yes, i did a bit of searching before attempting it, just to make sure there was any use to make of it after removing the electron gun itself. as i'm not intending to use it right away, all i'm interested in is a working part. however, i did read that replacing the internal filament of the gun with one made from a different alloy can make it work outside a vacuum. i dont remember how it was justified, but it seemed credible.

@betwixt - thanks for the info but as i dont care to service the tv but just take its electron gun, would FvM's method still work for that? is there any danger besides possible implosion? i've noticed some tape and really thick glue around the neck which i assumed was holding the gun there, but now that you mention holes, is it possible the tape covers old holes? they're pretty symmetrical around the neck so i dont think so, but since i dont have a drill, it would be convenient to find an old hole and just open it

 

[FvM]

i did read that replacing the internal filament of the gun with one made from a different alloy can make it work outside a vacuum

CRT tubes have indirectly heated cathodes, I can hardly imagine how to replace the filament with DIY techniques. And you still won't be able to operate an electron gun at atmospheric pressure with a free path length of some 100 nm.

 

[lynx_phoenix]

right, so i guess its pretty pointless to go through all the work and hazard to get an electron gun that i probably cant use anyway. i guess i'll just scrap the tv and do a search on how to actually make an electron gun in case i'm interested in the future

thanks for all the replies guys!

 

[betwixt]

I wouldn't even think about salvaging the gun for later. Apart from the obvious difficulty of needing a vacuum and some very high voltages to make it do anything useful, as soon as air reaches the cathode it will oxidize and lose efficiency and the magnesium gettering will fail. When a new electron gun is fitted to repair a tube, it has to be pumped to near vacuum state and then the internal magnesium ring is ignited in an induction oven. It's a one time processes, it can't be repeated, that gun is useless as soon as air reaches it a second time.

Brian.

 

[lynx_phoenix]

lol leave it to me to carry and keep a huge useless tv to get a part thats useless once removed

anyway, i guess that settles it for good - old tv -> junk

marking thread as solved