It's been a while, but I remember the degaussing coils built into the larger CRT's for sure. This is different, but I also remember as a kid my hair standing up when turning on the older TV sets in the 80's.... Those flybacks were no joke. Great video!
Thanks! Pretty much any color CRT has a degaussing coil other than small or unusual ones. It doesn't take much of a field to shift the electron beams a fraction of a mm to mess up the color by hitting the adjacent phosphor dot. I have heard that some large very fine pitch tubes actually needed to be adjusted to compensate for the direction of the earths magnetic field after the TV was installed. I once actually suggested to someone to use a fine pitch crt computer monitor as an AC magnetic field detector for a particular application. Your going to laugh - I have a number of CRT TVs and monitors including some of the last greatest HD TV flat-screen ones that I use every day (one TV, and one monitor). And when they are turned on you can hear the crackle as the 30kv builds up inside the crt and a mirror image of the same voltage builds up on the outside of the glass tube. And more than once I have gotten a good static zap from the screen.
I worked as a tech at an office equipment shop in the 90s that sold computers. They used to do high end desktop publishing setups as part of it and that meant big expensive high-res CRTs. There was a demo unit setup with a 21" or maybe 23" iiyama monitor and the salesman decide to rearrange it for a presentation. He turned off the monitor by pulling out the leads then picked it up with the face of the tube to his chest. When his fingers touched the metal chassis an audible crack sounded off and the expression on his face was priceless. He wanted to drop it like a hot potato but it was a pretty expensive monitor so he had no choice but to carefully put it down and grin and bear it. He didn't make that mistake again.
@@retrozmachine1189 Oops! I guess thats the cost of doing business. I remember how expensive monitors that size were as well as the workstations to drive them at resolutions of 1kx1k or more. I was a grad student in the early 90s and we had Sun workstations with monitors in that size range. If I recall correctly the cheaper systems were in the $25k range and the most expensive one we had was well over $100k. Amazing the our cell phones today have faster processors, more memory and higher resolution at less than $1k!
The degausing coil reminds me of my time as an apprentice (1991ish) at an electronics, computer and telecom repair shop. Repaired CRT monitors (which pack quite a punch 😂) and we were once called to a CAD company where one of their big and expensive monitors was suddenly displaying distorded and weird coloured images. When we came, we saw the phenomenon, shut off the display, disconnected it and moved it away to a spot where we could work on it, awai from the big fishtank next to the workplace. Opened it up, saw and smelled nothing strange, hooked it up to another computer, click and hum of degausing coil and an almost crisp image we adjusted... Put monitor bac together and hooked it up again on its own spot, distorted image!!! 😮 Then I saw the cleaning wiper on the out and inside of the glass of the fishtank, next to the edge of the monitor... Moved the wiper away, colours and distortions moved around as well. 😂 So parked wiper well away, switched monitor off and on again, degauss succesfull and we had a new story to tell 😉
I had heard that the larger, finer pitch CRTs were (not surprizingly) particularly sensitive to stray fields - really neat to hear an actual story of the consequences. I think I got the big old degassing coil at a hamfest or some such flea-market event. It was too neat vintage item to pass on and the video is the only time I have ever used it. I guess I was lucky enough never to have used a CRT monitor near a fishtank with a wiper :)
Years ago when I had a TV with a CRT, I turned off my vacuum cleaner while it was near the TV. The residual magnetism made a color blotch that was so strong, the built in de-gaussing coil wouldn't clear it. It took a special external de-gaussing coil.
Your lucky someone knew what they were doing in terms of degaussing. We had a TV that had a blotch (no idea what caused it - was borrowed from a relative) and no repair shop knew what the problem was or that demagnetizing would be the fix. Interesting that the stray fields from the vacuum were enough to mess it up. I guess that shows how sentsitive some CRTs are.I have heard of large fine pitch ones that needed the purity adjustment redone after re-positioning because the earths filed was enough to mis-align the electron beams.
So glad you enjoyed it! Degaussing color TV tubes is a certainly something that an ever decreasing number of people would even know about. Glad you subscribed - more videos to come!
If you have a soldering gun, you can demagnetize an object like a tweezer by moving it in and out of the soldering iron's loop while the trigger is pressed. I've been doing it for years to demagnetize my SMD tweezers.
Very interesting. I remember back in the mid 80's when the guy I was working with had bought a new TV and his little kid called him in the room and proudly stated, "look what I can do daddy." He walked in to see his child moving a magnet across the screen making pretty colors (that never went away), To bad we didn't know about this trick with the soldering gun back then.
Back when color TVs were expensive - Oops! We had a TV in the 70s that had a color blotch in a lower corner. No-one back then knew how to fix it. I'm surprised most TV repair shops weren't aware at how to demagnetize things. It cant have been an uncommon problem, and could have been easy repair money.
I had a Montgomery Ward TV circa 1984 that lacked a built in degauss function. With all my tinkering with speaker magnets and other electronic projects, I managed to magnetize the mask and had permanent color blotches on the screen that I lived with for about 10 years because I didn't know how to degauss it myself. Thanks for another cool video.
Oops! When I was kid I did hold a magnet close enough to our color TV that the colors distorted. Luckily not so close that there was a permanent blotch or I would have been in trouble! But we did have another TV a bit later that had a permanent blotch that no-one was been able to repair. I wonder if some TVs did not have the built in degaussing circuit, or if for some the thermister that activated the coil for a few seconds at startup would eventually fail . Glad you liked the video!
@@ElectromagneticVideos In 1991, I worked at a bowling alley with 44 lanes. We replaced the old electronic scoring system with a new one, which meant 44 new small monitors on the scoring table and 44 new big ones up above, all of which were CRT's. (One of the last steps after installation was to degauss all of those monitors, which was a lot of fun. They wouldn't let me take that degauss coil home, though. Incidentally, if you're interested in computer history at all, the back end of that scoring system ran on a Data General desktop PC with a 386 processor and ran SCO Xenix to control a bunch of serial interfaces to all the lane scoring computers as well as the serial terminals at the front counter and the power switches for the lanes. I appreciate your videos and the replies!
@@MichaelCowden 44+44 monitors - that must have been really expensive back then! SCO Xenix - never used it but heard of it. Back then I was grad student and Sun workstations running their version of Unix called Solaris ruled in our lab. I also remember what an advance the 386 was - for the first time full memory management and virtual memory for the PCs - and some of us started running a brand new Unix-like OS at home called Linux! I appreciate your (and other peoples) comments! Its so interesting to hear stories and experiences about related topics. And I always learn something!
Ooops, I rolled my 4x12 guitar cabinet out the house past the tv onetime and made it all purple and green. This is when I learned the term Degaussing! I think it fixed itself after a few power cycles.
Speaker magnets in the cabinet maybe? Most color TVs had a built in degaussing coil attached to a thermister - you can often hear a hum for a second or two when the TV is switched on. Over the course of a second the thermister heats up gradually reducing the field though the degaussing coil hopefully demagnetizing the CRT and parts around it. My memory of this is one TV we had when I was kid had an orange blotch in the bottom corner of the CRT. No-one TV repair man was ever able to fix it - I'm guessing back then without the internet understanding degaussing was not as well known or easy to find out about.
@@ElectromagneticVideos Right bro! Those 12 inch speakers have huge magnets and unshielded cabinet. I was working in low volt integrated systems on custom homes at the time so a friend told me about degaussing it if needed. Few years later I had an LED module go bad on my rear projection 50" tv so we had to watch my kids Wifgkes dvds in wierd colors for about a week till I got the parts and learned online how to swap that red module that burns hotter with some silver paste and turn down the factory settings! I also spliced in an extra pc fan to blow across the little radiators for each RGB module and it lasted for years till pixels started dying so much it looked like a starry night on screen and no good fix for that!
@@THRASHMETALFUNRIFFS Thats an impressive fix. We are so lucky these days with all the info that is avail;able online. I have fixed things in my car that would been impossible without watching step-by step videos
I know we must go with the current theory accepted by the scientific community but I left you my theory on the magnitization link you provided. Thank you for the videos. Subscribed. I appreciate the back and fourth exchange.
Exactly! If one had an easy way of measuring the the field you could in theory setup a properly oriented coil and gradually increase an opposing field from the coil till you pushed the point on the BH curve down to B=0, but hard to get that right. Much easier with an AC field that gradually is diminished by moving the coil away or decreasing the current until one works the field down to the 0,0 point on the BH curve.
New subscriber here. Loved your explanation of magnetic domains and region growing from the last video. Hope you have more videos planned for magnetism :D
Thank you so much! I have a few more magnetism ones planned for the near future, then some focusing on electric fields, and then some on electromagnetic waves (aka radio waves, light, uv, xrays etc) in free space and in transmission lines (ie coax cable) and optical fibers or wave-guides. Same sort of approach - try and give a sense of underlying theory and how things work with diving deeply into the math. And with losts of experiments of course!
After getting a magnet really hot then immediately placing it in a strong flux field and allowing it to cool down while still in a magnetic field, will it be a good way to achieve a strong magnet once again?
That sure seems like it would be right. I have never tried it and a quick bit of research didnt turn up much. It would be interesting to know if magnetizing by cooling in a field produces a slightly stronger magnet than one could achieve applying the field when the material is cold. I would suspect at best the improvement would be marginal since we are normally magnetizing things to their saturation point. Perhaps cooling from hot might alight the last tiny percentage of domains but again its probably a minimal effect. Most strong magnets are manufactured by sintering a powder (heat+pressure) into the desired shape. And this is apparently done in a magnetic field to align the tiny particles before they solidify to presumably improve magnetic properties in the desired direction.They are then charged by applying a strong field to the magnet once the material is cooled. I would guess if there was an advantage of charging while cooling they would do that. A few related things: in the previous video I mention how cooling lava in the earths field becomes a magnet in the fields direction, effectively doing what you described, just poorer magnetic material and weaker field - I have always though that imprinting of the earths field was neat. And do you have a rice cooker? Most turn off using a chunk of material with a Curie temperature of just above boiling right and a magnet with a much higher Curie temperature. The magnet remains magnetic all the time, but the other material looses its magnetic properties and ceases to be attracted to the magnet when above the boiling point of water ie when the rice is ready - and flips a switch. The only application of Curie temperature I can think of. Thanks for the interesting question!
As long i renember playing with magnets and tvs, even old ones B&W vacuum lamp tvs recovers if i let them turned off for hours. Didn't knew demagnetizer for tv existed, i for someone who never turn off the tv i suppose :)
The reason color TV CRTs dont recover as well and need a demagnetizer is they metal mesh just behind the screen surface that can get magnetized. And worse, that mesh is used to make sure the three color electron streams hit the correctly colored phosphors on the screen surface. The slightest deviation such as caused by a magnetic field causes the colors to shift. The plain old BW CRT has a lot less metal around it to get magnetized, and even if it does, the image may shift slightly but often without being noticed.
@@ElectromagneticVideos I know, i'm electronician too, in fact i buyed only 1 crt tv when i was young and all others was tv that people thrown away generally bigger everytime, i repaired a lot, tv was expensive at that time and not a lot of money, now you found big flat tv laying around in streets people change and don't repair, in most cases it's only the condensators of the power supply that need to be changed but you know that. I played with magnets with somes and i don't lie, when i let them off for hours, they recover, no problem.
@@nln1515 I did the same thing - while I was a student my TVs were always ones that had been thrown out. Like yours, mine got bigger and bigger, and the final one I had was a "giant" (well for that time) 25 inch color RCA. I had it for years ....
Could you use a magnet attached to a motor shaft, to spin it around, to degauss a crt? Might have to make it larger by using 2 or more magnets attached to a steel rod. Also, could I wind a large area coil and use the current from that soldering (in place of the tip) as a degaussing coil. I have an old oscilloscope with very wonky looking traces after moving from the southern hemisphere and I can’t help but think the earths magnetic field is very different and causing the bad display. Similar to turning your old crt tv upside down.
You could - spinning magnets like that will make an AC field. But usually magnets are so small the field is concentrated close to them so they dont cover a large volume as one might need for a CRT Winding a large coil is the way to go. If the coil was thick, like one or two loops of #14 or #12 AWG wires, you could power it with a soldering gun (careful not to leave it on too long - might heat up the wire!) . If you went with many turns of thinner wires, something like 6V or 12V AC from a transformer would probably be needed. Very odd that that the earths field would mess up a presumably single gun crt like that. Does the wonky nature change if you point the scope in another direction? If not, maybe the case or supports somehow got magnetized in transit. Or is the AC voltage a bit off depending on where you are/were? With some places having as low as 220V or as much as 240V, I can imagine an ageing power supply capacitor having troubling filtering some voltages particularity at the low end.
Hi, this is an amazing video thank you for sharing your knowledge. I am working on a project where I have to build equipment to magnetize and demagnetize a permanent magnet. I saw both your re-magnetize and de-magnetize videos. So to conclude, to magnetize a permanent magnet I need to use a DC source to power the coil, and to De-magnetize a magnet I need to use an AC source to power the coil? Do we have any formula to calculate how strong the magnetic field of permanent magnet will become in relation to amount of time it was kept inside the electro-magnet?
The trick to demagnetizing is is you have to slowly reduce the strength of the AC field. If you turn it off abruptly the results are unpredictable. TVs use a thermister to gradually reduce the current after turning on (the thermister heats up and increases its resistance to reducing current to the coil). Time to magnetize is very short. Fractions of a second. The key is having a field stronger than the saturation value of the metal in the magnet. If you need to turn a magnet on or off, why not just use an electromagnet?
Actually, the product I am working on is a reed switch. Reed switches are magnetic switches most of all they are all form A type which is a normally open switch. TO change it to a Normally closed switch we embed a permanent magnet on the outerside of the glass. Which makes the switch as bistable switch. When these reed switches comes under reverse polarity electro magnetic field the magnet get nullified and switch becomes normally open. The Ampere turns of the electromagnet is sometimes high and sometimes less to nullify the magnet. So,in an attempt to make all the switches have uniform Pullin values I am working on altering the permanent magnet's magnetic intensity. if the magnet is too strong then I have to demagnetize it. So, in short I want to build a machine that magnetizes and demagnetizes the permanent magnet.
Very interesting Sir. I am trying to make a horse shoe magnet like the first commercial electric lap steel guitars from Rickenbacher from around 1932. I use pretty hard steel, bend it to a U shaped form and then try to magnetise this with the help of a microwave transformer. As current source I have a welding machine +/- 45 V AC and a diode bridge of heavy diodes to turn the AC to DC for the primary coil of the microwave transformer. This works good, but i was thinking of using another welder coil as charging unit. In my setup i have +/- 45 volts DC from one welder applied to coil of the second welder. A high current is flowing, but the result does not look better. So my question is, what is the relationship between number of turns, thickness of the coil of the charging unit and the voltage applied to it from the source transformer or battery to make a really strong magnetiser? In other words is voltage more important than current? Thank you for a reply.
What a neat project! So the more amp turns the better. You may be finding the lower voltage out of the second wekder is so low the current drops. If you hanvt already, get a clamp on ammeter that does DC (not all do) so you can see the current. You may also be simply have the core at its saturatration level so more current will have a minimal increase inthe final magnetic field. Also, while hard magnetic materials are good, steel cant compete with the more advanced magnetic materials. I wonder how good the magnets like you describe were back in the old days?
Another option for high current DC is a rectiformer. In the lab I used to work in, we had I think a 600A unit that could be wound up to 70 volts. It did require a 3 phase AC supply though.
@@liam3284 I had to look up rectiformer. Interesting. So what did you use that amount of current for? Things I saw online was for applications like aluminum refining.
Sir I would like for u to do a video on why it was good for civiliazation demagnetize things. For example I have a question can u magnetize humans and can u magnetize your building 🏢? Will this attract lightning ⚡? So many questions ❓
So every time you challenge a permanent magnet with another magnet with an opposite pole (n to s) does it remove some of the remanence because you are going down the hysteresis curve towards the coerciveness? Would a magnetized keeper destroy the horse shoe magnet, especially if you used an N52?
Yes - exactly - the more you manage to push the point down the hysteresis curve, the more you have demagnetized it. If the keeper was magnetized and you forced its N to touch the horseshoe N (and same for S) it will deteriorate the magnet. If you put the magnetized keeper on so its N touches the horseshoe S(and same for the other ends) it will help sustain - or even strengthen the horseshoe magnet. I keep the bar magnets on top of each other, N to S etc to help they stay strong and the same for the horseshoe ones. The idea is to make a nice easy circuit for the field to flow though. The one good thing is that when magnets aren't touching but oriented N to N or S to S so they repel, the air gaps alters the characteristics of the magnetic circuit weakening the demagnetizing effect so in things like motors designed properly the magnets stay strong is spite of being subjects to a certain degree of reverse field.
Can you speak to the emergency shutoff method used for MRI machines? I have heard that it uses extreme cold (perhaps using liquid nitrogen?) to disable the magnet in an emergency situation. Is that just relevant with electromagnets?
You just sent me down a fascinating rabbit hole of MRI machine stuff! I actually took a grad course on superconducting magnets years ago, but never did we discuss the need of emergency shutdowns. To do an emergency shutdown of a superconducting magnet of any kind, including those in an MRI, you can raise the temperature in the superconductor till get gets warm enough to revert back to being a regular conductor. "Warm enough" may still be hundreds of degrees below zero. From what I just read, and I'm no expert on MRIs, it looks like they do some combination of either draining the liquid liquid helium out of the machine, and turning on an electric heater to evaporate the liquid helium. Once the helium s gone (its the helium that keeps the superconductor at a low temperature), the superconductor becomes a regular conductor, and its magnetic field drops rapidly as the current flowing in no-longer superconductor looses its energy in the resistance of the wire. further heating it up speeding up the quenching process. Looks like its quite violent - vast amounts of helium gas are boiled off really quickly, and the rapid heating of the superconducting magnet and other parts often (always?) causes damage to the machine that will need to be repaired. Looks like potentially 10s of thousand of $ damage, so apparently they avoid that sort of shutdown except in a real emergency! Thanks for a fascinating question!
@@davidc7763 Unfortunately most practical superconductors need to be that cold. You may have heard in the news that are issues with the world Helium supply which is a real concern for MRI machines. Hopefully gas wells with significant helium content will have it extracted and alleviate the situation in the future.
I just looked on the CRT monitor I use (for photography) and it too has the degassing function in the menu. Just tried it - very similar to in the video with the external coil near the TV. Having said that - you were wise not to have used it - if something did go wrong like the thermistor used slowly reduce the AC through the coil failing, one could potentially end up with the monitor in a worse state.
The manual degauss was mainly there to cover the instances where you turned the monitor or moved it a bit while you already had it on. Reorienting the shadow mask could result in poor colour so you'd press the button and get an instant degauss instead of turning off, waiting for the thermistor to cool and turning back on. Hi-res and professional monitors often had a relay as well as the thermistor to ensure no wiggle in the picture from any residual current passing through the thermistor once it got hot. TVs usually just had the thermistor.
@@retrozmachine1189 Interesting! I just did the degauss function on my monitor and sure enough you can hear the relay click on on off. And your right - I dont hear that on the TVs! Thanks so much for that tidbit of information!
Ebay - its a vintage piece of equipment. Unfortunatluy they dont make them any more. You could make your own by winding a coil on a suitable frame of some kind (doesn't have to circular - could be rectangular).
I'll bet! Depending on when that was, colo TVs were expensive! I actually tried a magnet near the our color TV but was lucky enough not to get it close enough to result in what what happened to you. I guess over time the built in demagentizer took care of you problem. We also had a borrowed color TV for a while before we had our own - it was lent to us because it had a big orange colored area near the bottom right of the screen that no repairman had been able to fix. Who knows if they were taught how to handle magnetization like that, or if the actual shadow mask was somehow warped for some other reason. I also remember one of my dads co-workers getting a color TV very cheap from a dealer because it had a similar problem, so I guess way back it wasn't uncommon to have issues like that.
YOu mean use its fields to degauss things? Yes. But the fields are usually well confined so nott great. But - here is a trick I once used. Remove the rotor and side from a standard small induction motor. Disconnect the starter winding. Use a 12V AC transformer to power it - I used an old battery charger with the rectifiers removed. Now turn in on and slowly mover something - maybe a jar of nails in and out. And do it carefully enough and they are demagnetized!
Yes! The critical temperature is the Curie temperature which can vary quite a bit from material to material. Also works the other way - heating something up and let it cool in a magnetic field and will become magnetized.
Наука
It's been a while, but I remember the degaussing coils built into the larger CRT's for sure. This is different, but I also remember as a kid my hair standing up when turning on the older TV sets in the 80's.... Those flybacks were no joke. Great video!
Thanks! Pretty much any color CRT has a degaussing coil other than small or unusual ones. It doesn't take much of a field to shift the electron beams a fraction of a mm to mess up the color by hitting the adjacent phosphor dot. I have heard that some large very fine pitch tubes actually needed to be adjusted to compensate for the direction of the earths magnetic field after the TV was installed. I once actually suggested to someone to use a fine pitch crt computer monitor as an AC magnetic field detector for a particular application.
Your going to laugh - I have a number of CRT TVs and monitors including some of the last greatest HD TV flat-screen ones that I use every day (one TV, and one monitor). And when they are turned on you can hear the crackle as the 30kv builds up inside the crt and a mirror image of the same voltage builds up on the outside of the glass tube. And more than once I have gotten a good static zap from the screen.
@@ElectromagneticVideos awesome!
I worked as a tech at an office equipment shop in the 90s that sold computers. They used to do high end desktop publishing setups as part of it and that meant big expensive high-res CRTs. There was a demo unit setup with a 21" or maybe 23" iiyama monitor and the salesman decide to rearrange it for a presentation. He turned off the monitor by pulling out the leads then picked it up with the face of the tube to his chest. When his fingers touched the metal chassis an audible crack sounded off and the expression on his face was priceless. He wanted to drop it like a hot potato but it was a pretty expensive monitor so he had no choice but to carefully put it down and grin and bear it. He didn't make that mistake again.
@@retrozmachine1189 Oops! I guess thats the cost of doing business. I remember how expensive monitors that size were as well as the workstations to drive them at resolutions of 1kx1k or more. I was a grad student in the early 90s and we had Sun workstations with monitors in that size range. If I recall correctly the cheaper systems were in the $25k range and the most expensive one we had was well over $100k. Amazing the our cell phones today have faster processors, more memory and higher resolution at less than $1k!
The degausing coil reminds me of my time as an apprentice (1991ish) at an electronics, computer and telecom repair shop.
Repaired CRT monitors (which pack quite a punch 😂) and we were once called to a CAD company where one of their big and expensive monitors was suddenly displaying distorded and weird coloured images.
When we came, we saw the phenomenon, shut off the display, disconnected it and moved it away to a spot where we could work on it, awai from the big fishtank next to the workplace.
Opened it up, saw and smelled nothing strange, hooked it up to another computer, click and hum of degausing coil and an almost crisp image we adjusted...
Put monitor bac together and hooked it up again on its own spot, distorted image!!! 😮
Then I saw the cleaning wiper on the out and inside of the glass of the fishtank, next to the edge of the monitor...
Moved the wiper away, colours and distortions moved around as well. 😂
So parked wiper well away, switched monitor off and on again, degauss succesfull and we had a new story to tell 😉
I had heard that the larger, finer pitch CRTs were (not surprizingly) particularly sensitive to stray fields - really neat to hear an actual story of the consequences.
I think I got the big old degassing coil at a hamfest or some such flea-market event. It was too neat vintage item to pass on and the video is the only time I have ever used it. I guess I was lucky enough never to have used a CRT monitor near a fishtank with a wiper :)
Years ago when I had a TV with a CRT, I turned off my vacuum cleaner while it was near the TV.
The residual magnetism made a color blotch that was so strong, the built in de-gaussing coil wouldn't clear it.
It took a special external de-gaussing coil.
Your lucky someone knew what they were doing in terms of degaussing. We had a TV that had a blotch (no idea what caused it - was borrowed from a relative) and no repair shop knew what the problem was or that demagnetizing would be the fix.
Interesting that the stray fields from the vacuum were enough to mess it up. I guess that shows how sentsitive some CRTs are.I have heard of large fine pitch ones that needed the purity adjustment redone after re-positioning because the earths filed was enough to mis-align the electron beams.
Fondly remember the first time I saw and subsequently used one of those degaussing coils!
Great video, thank you!
Immediate Subscription!
So glad you enjoyed it! Degaussing color TV tubes is a certainly something that an ever decreasing number of people would even know about.
Glad you subscribed - more videos to come!
If you have a soldering gun, you can demagnetize an object like a tweezer by moving it in and out of the soldering iron's loop while the trigger is pressed. I've been doing it for years to demagnetize my SMD tweezers.
I should have mentioned that! Thank you so much for pointing it out - hopefully it will help someone who reads this!
Very interesting. I remember back in the mid 80's when the guy I was working with had bought a new TV and his little kid called him in the room and proudly stated, "look what I can do daddy." He walked in to see his child moving a magnet across the screen making pretty colors (that never went away), To bad we didn't know about this trick with the soldering gun back then.
Back when color TVs were expensive - Oops! We had a TV in the 70s that had a color blotch in a lower corner. No-one back then knew how to fix it. I'm surprised most TV repair shops weren't aware at how to demagnetize things. It cant have been an uncommon problem, and could have been easy repair money.
@@ElectromagneticVideos - Agreed. I think my buddy thought it was just ruined forever and bought a new TV.
@@justadbeer What a shame :(
Oppsies I did that, Luckily the TV was rented.
@@dogwalker666 "It just broke" . I had forgotten way back when you could rent TVs.
I had a Montgomery Ward TV circa 1984 that lacked a built in degauss function. With all my tinkering with speaker magnets and other electronic projects, I managed to magnetize the mask and had permanent color blotches on the screen that I lived with for about 10 years because I didn't know how to degauss it myself. Thanks for another cool video.
Oops! When I was kid I did hold a magnet close enough to our color TV that the colors distorted. Luckily not so close that there was a permanent blotch or I would have been in trouble! But we did have another TV a bit later that had a permanent blotch that no-one was been able to repair. I wonder if some TVs did not have the built in degaussing circuit, or if for some the thermister that activated the coil for a few seconds at startup would eventually fail . Glad you liked the video!
@@ElectromagneticVideos In 1991, I worked at a bowling alley with 44 lanes. We replaced the old electronic scoring system with a new one, which meant 44 new small monitors on the scoring table and 44 new big ones up above, all of which were CRT's. (One of the last steps after installation was to degauss all of those monitors, which was a lot of fun. They wouldn't let me take that degauss coil home, though. Incidentally, if you're interested in computer history at all, the back end of that scoring system ran on a Data General desktop PC with a 386 processor and ran SCO Xenix to control a bunch of serial interfaces to all the lane scoring computers as well as the serial terminals at the front counter and the power switches for the lanes. I appreciate your videos and the replies!
@@MichaelCowden 44+44 monitors - that must have been really expensive back then! SCO Xenix - never used it but heard of it. Back then I was grad student and Sun workstations running their version of Unix called Solaris ruled in our lab. I also remember what an advance the 386 was - for the first time full memory management and virtual memory for the PCs - and some of us started running a brand new Unix-like OS at home called Linux!
I appreciate your (and other peoples) comments! Its so interesting to hear stories and experiences about related topics. And I always learn something!
Ooops, I rolled my 4x12 guitar cabinet out the house past the tv onetime and made it all purple and green.
This is when I learned the term Degaussing! I think it fixed itself after a few power cycles.
Speaker magnets in the cabinet maybe? Most color TVs had a built in degaussing coil attached to a thermister - you can often hear a hum for a second or two when the TV is switched on. Over the course of a second the thermister heats up gradually reducing the field though the degaussing coil hopefully demagnetizing the CRT and parts around it.
My memory of this is one TV we had when I was kid had an orange blotch in the bottom corner of the CRT. No-one TV repair man was ever able to fix it - I'm guessing back then without the internet understanding degaussing was not as well known or easy to find out about.
@@ElectromagneticVideos Right bro! Those 12 inch speakers have huge magnets and unshielded cabinet. I was working in low volt integrated systems on custom homes at the time so a friend told me about degaussing it if needed. Few years later I had an LED module go bad on my rear projection 50" tv so we had to watch my kids Wifgkes dvds in wierd colors for about a week till I got the parts and learned online how to swap that red module that burns hotter with some silver paste and turn down the factory settings! I also spliced in an extra pc fan to blow across the little radiators for each RGB module and it lasted for years till pixels started dying so much it looked like a starry night on screen and no good fix for that!
@@THRASHMETALFUNRIFFS Thats an impressive fix. We are so lucky these days with all the info that is avail;able online. I have fixed things in my car that would been impossible without watching step-by step videos
I know we must go with the current theory accepted by the scientific community but I left you my theory on the magnitization link you provided. Thank you for the videos.
Subscribed. I appreciate the back and fourth exchange.
Glad you subscribed - always appreciate that!
I responded to the comment you mentioned ...
I was hoping for this since your last video thank you
Your welcome! Glad you liked it!
Always enjoy your videos. Thanks for sharing
Thanks! I really appreciate that!
Now I remember this video. Hysteresis is what allows you to demagnetise in several passes of diminishing field strength.
Exactly! If one had an easy way of measuring the the field you could in theory setup a properly oriented coil and gradually increase an opposing field from the coil till you pushed the point on the BH curve down to B=0, but hard to get that right. Much easier with an AC field that gradually is diminished by moving the coil away or decreasing the current until one works the field down to the 0,0 point on the BH curve.
Excellent demonstration ❤
Thanks! Glad you liked it!
Nice presentation
Thanks!
New subscriber here. Loved your explanation of magnetic domains and region growing from the last video. Hope you have more videos planned for magnetism :D
Thank you so much! I have a few more magnetism ones planned for the near future, then some focusing on electric fields, and then some on electromagnetic waves (aka radio waves, light, uv, xrays etc) in free space and in transmission lines (ie coax cable) and optical fibers or wave-guides. Same sort of approach - try and give a sense of underlying theory and how things work with diving deeply into the math. And with losts of experiments of course!
@@ElectromagneticVideos Sounds great! Looking forward to them!
@@ishwarm5842 Great!
Great and interesting stuff, wish your channel success! Thanks
Thank you so much! I really appreciate it!
After getting a magnet really hot then immediately placing it in a strong flux field and allowing it to cool down while still in a magnetic field, will it be a good way to achieve a strong magnet once again?
That sure seems like it would be right. I have never tried it and a quick bit of research didnt turn up much.
It would be interesting to know if magnetizing by cooling in a field produces a slightly stronger magnet than one could achieve applying the field when the material is cold. I would suspect at best the improvement would be marginal since we are normally magnetizing things to their saturation point. Perhaps cooling from hot might alight the last tiny percentage of domains but again its probably a minimal effect.
Most strong magnets are manufactured by sintering a powder (heat+pressure) into the desired shape. And this is apparently done in a magnetic field to align the tiny particles before they solidify to presumably improve magnetic properties in the desired direction.They are then charged by applying a strong field to the magnet once the material is cooled. I would guess if there was an advantage of charging while cooling they would do that.
A few related things: in the previous video I mention how cooling lava in the earths field becomes a magnet in the fields direction, effectively doing what you described, just poorer magnetic material and weaker field - I have always though that imprinting of the earths field was neat. And do you have a rice cooker? Most turn off using a chunk of material with a Curie temperature of just above boiling right and a magnet with a much higher Curie temperature. The magnet remains magnetic all the time, but the other material looses its magnetic properties and ceases to be attracted to the magnet when above the boiling point of water ie when the rice is ready - and flips a switch. The only application of Curie temperature I can think of.
Thanks for the interesting question!
As long i renember playing with magnets and tvs, even old ones B&W vacuum lamp tvs recovers if i let them turned off for hours.
Didn't knew demagnetizer for tv existed, i for someone who never turn off the tv i suppose :)
The reason color TV CRTs dont recover as well and need a demagnetizer is they metal mesh just behind the screen surface that can get magnetized. And worse, that mesh is used to make sure the three color electron streams hit the correctly colored phosphors on the screen surface. The slightest deviation such as caused by a magnetic field causes the colors to shift. The plain old BW CRT has a lot less metal around it to get magnetized, and even if it does, the image may shift slightly but often without being noticed.
@@ElectromagneticVideos I know, i'm electronician too, in fact i buyed only 1 crt tv when i was young and all others was tv that people thrown away generally bigger everytime, i repaired a lot, tv was expensive at that time and not a lot of money, now you found big flat tv laying around in streets people change and don't repair, in most cases it's only the condensators of the power supply that need to be changed but you know that.
I played with magnets with somes and i don't lie, when i let them off for hours, they recover, no problem.
@@nln1515 I did the same thing - while I was a student my TVs were always ones that had been thrown out. Like yours, mine got bigger and bigger, and the final one I had was a "giant" (well for that time) 25 inch color RCA. I had it for years ....
Could you use a magnet attached to a motor shaft, to spin it around, to degauss a crt? Might have to make it larger by using 2 or more magnets attached to a steel rod. Also, could I wind a large area coil and use the current from that soldering (in place of the tip) as a degaussing coil. I have an old oscilloscope with very wonky looking traces after moving from the southern hemisphere and I can’t help but think the earths magnetic field is very different and causing the bad display. Similar to turning your old crt tv upside down.
You could - spinning magnets like that will make an AC field. But usually magnets are so small the field is concentrated close to them so they dont cover a large volume as one might need for a CRT
Winding a large coil is the way to go. If the coil was thick, like one or two loops of #14 or #12 AWG wires, you could power it with a soldering gun (careful not to leave it on too long - might heat up the wire!) . If you went with many turns of thinner wires, something like 6V or 12V AC from a transformer would probably be needed.
Very odd that that the earths field would mess up a presumably single gun crt like that. Does the wonky nature change if you point the scope in another direction? If not, maybe the case or supports somehow got magnetized in transit. Or is the AC voltage a bit off depending on where you are/were? With some places having as low as 220V or as much as 240V, I can imagine an ageing power supply capacitor having troubling filtering some voltages particularity at the low end.
Hi, this is an amazing video thank you for sharing your knowledge. I am working on a project where I have to build equipment to magnetize and demagnetize a permanent magnet. I saw both your re-magnetize and de-magnetize videos. So to conclude, to magnetize a permanent magnet I need to use a DC source to power the coil, and to De-magnetize a magnet I need to use an AC source to power the coil? Do we have any formula to calculate how strong the magnetic field of permanent magnet will become in relation to amount of time it was kept inside the electro-magnet?
The trick to demagnetizing is is you have to slowly reduce the strength of the AC field. If you turn it off abruptly the results are unpredictable. TVs use a thermister to gradually reduce the current after turning on (the thermister heats up and increases its resistance to reducing current to the coil).
Time to magnetize is very short. Fractions of a second. The key is having a field stronger than the saturation value of the metal in the magnet.
If you need to turn a magnet on or off, why not just use an electromagnet?
Actually, the product I am working on is a reed switch. Reed switches are magnetic switches most of all they are all form A type which is a normally open switch. TO change it to a Normally closed switch we embed a permanent magnet on the outerside of the glass. Which makes the switch as bistable switch. When these reed switches comes under reverse polarity electro magnetic field the magnet get nullified and switch becomes normally open. The Ampere turns of the electromagnet is sometimes high and sometimes less to nullify the magnet. So,in an attempt to make all the switches have uniform Pullin values I am working on altering the permanent magnet's magnetic intensity. if the magnet is too strong then I have to demagnetize it. So, in short I want to build a machine that magnetizes and demagnetizes the permanent magnet.
@@abishekmoorthi2779 Sounds like a very interesting project. Best of luck with success!
Very interesting Sir. I am trying to make a horse shoe magnet like the first commercial electric lap steel guitars from Rickenbacher from around 1932. I use pretty hard steel, bend it to a U shaped form and then try to magnetise this with the help of a microwave transformer. As current source I have a welding machine +/- 45 V AC and a diode bridge of heavy diodes to turn the AC to DC for the primary coil of the microwave transformer. This works good, but i was thinking of using another welder coil as charging unit.
In my setup i have +/- 45 volts DC from one welder applied to coil of the second welder. A high current is flowing, but the result does not look better.
So my question is, what is the relationship between number of turns, thickness of the coil of the charging unit and the voltage applied to it from the source transformer or battery to make a really strong magnetiser? In other words is voltage more important than current?
Thank you for a reply.
What a neat project! So the more amp turns the better. You may be finding the lower voltage out of the second wekder is so low the current drops. If you hanvt already, get a clamp on ammeter that does DC (not all do) so you can see the current. You may also be simply have the core at its saturatration level so more current will have a minimal increase inthe final magnetic field. Also, while hard magnetic materials are good, steel cant compete with the more advanced magnetic materials. I wonder how good the magnets like you describe were back in the old days?
Another option for high current DC is a rectiformer. In the lab I used to work in, we had I think a 600A unit that could be wound up to 70 volts. It did require a 3 phase AC supply though.
@@liam3284 I had to look up rectiformer. Interesting. So what did you use that amount of current for? Things I saw online was for applications like aluminum refining.
Sir I would like for u to do a video on why it was good for civiliazation demagnetize things. For example I have a question can u magnetize humans and can u magnetize your building 🏢? Will this attract lightning ⚡? So many questions ❓
So every time you challenge a permanent magnet with another magnet with an opposite pole (n to s) does it remove some of the remanence because you are going down the hysteresis curve towards the coerciveness? Would a magnetized keeper destroy the horse shoe magnet, especially if you used an N52?
Yes - exactly - the more you manage to push the point down the hysteresis curve, the more you have demagnetized it.
If the keeper was magnetized and you forced its N to touch the horseshoe N (and same for S) it will deteriorate the magnet. If you put the magnetized keeper on so its N touches the horseshoe S(and same for the other ends) it will help sustain - or even strengthen the horseshoe magnet.
I keep the bar magnets on top of each other, N to S etc to help they stay strong and the same for the horseshoe ones. The idea is to make a nice easy circuit for the field to flow though.
The one good thing is that when magnets aren't touching but oriented N to N or S to S so they repel, the air gaps alters the characteristics of the magnetic circuit weakening the demagnetizing effect so in things like motors designed properly the magnets stay strong is spite of being subjects to a certain degree of reverse field.
Can you speak to the emergency shutoff method used for MRI machines? I have heard that it uses extreme cold (perhaps using liquid nitrogen?) to disable the magnet in an emergency situation. Is that just relevant with electromagnets?
You just sent me down a fascinating rabbit hole of MRI machine stuff! I actually took a grad course on superconducting magnets years ago, but never did we discuss the need of emergency shutdowns.
To do an emergency shutdown of a superconducting magnet of any kind, including those in an MRI, you can raise the temperature in the superconductor till get gets warm enough to revert back to being a regular conductor. "Warm enough" may still be hundreds of degrees below zero. From what I just read, and I'm no expert on MRIs, it looks like they do some combination of either draining the liquid liquid helium out of the machine, and turning on an electric heater to evaporate the liquid helium. Once the helium s gone (its the helium that keeps the superconductor at a low temperature), the superconductor becomes a regular conductor, and its magnetic field drops rapidly as the current flowing in no-longer superconductor looses its energy in the resistance of the wire. further heating it up speeding up the quenching process.
Looks like its quite violent - vast amounts of helium gas are boiled off really quickly, and the rapid heating of the superconducting magnet and other parts often (always?) causes damage to the machine that will need to be repaired. Looks like potentially 10s of thousand of $ damage, so apparently they avoid that sort of shutdown except in a real emergency!
Thanks for a fascinating question!
@@ElectromagneticVideos oh wow, I never considered that the liquid helium was part of the standard operating temperature.
@@davidc7763 Unfortunately most practical superconductors need to be that cold. You may have heard in the news that are issues with the world Helium supply which is a real concern for MRI machines. Hopefully gas wells with significant helium content will have it extracted and alleviate the situation in the future.
i had a old crt computer monitor and in the menu of the monitor is has a degaussing function. I never used it since the colors were always fine.
I just looked on the CRT monitor I use (for photography) and it too has the degassing function in the menu. Just tried it - very similar to in the video with the external coil near the TV. Having said that - you were wise not to have used it - if something did go wrong like the thermistor used slowly reduce the AC through the coil failing, one could potentially end up with the monitor in a worse state.
The manual degauss was mainly there to cover the instances where you turned the monitor or moved it a bit while you already had it on. Reorienting the shadow mask could result in poor colour so you'd press the button and get an instant degauss instead of turning off, waiting for the thermistor to cool and turning back on. Hi-res and professional monitors often had a relay as well as the thermistor to ensure no wiggle in the picture from any residual current passing through the thermistor once it got hot. TVs usually just had the thermistor.
@@retrozmachine1189 Interesting! I just did the degauss function on my monitor and sure enough you can hear the relay click on on off. And your right - I dont hear that on the TVs! Thanks so much for that tidbit of information!
Plz where did you buy the coil demagnetizer ?
Ebay - its a vintage piece of equipment. Unfortunatluy they dont make them any more. You could make your own by winding a coil on a suitable frame of some kind (doesn't have to circular - could be rectangular).
When I was a kid I left a rainbow spot on the TV..
Man I was in trouble. It went away after a few days..
Shew..
I'll bet! Depending on when that was, colo TVs were expensive! I actually tried a magnet near the our color TV but was lucky enough not to get it close enough to result in what what happened to you. I guess over time the built in demagentizer took care of you problem.
We also had a borrowed color TV for a while before we had our own - it was lent to us because it had a big orange colored area near the bottom right of the screen that no repairman had been able to fix. Who knows if they were taught how to handle magnetization like that, or if the actual shadow mask was somehow warped for some other reason. I also remember one of my dads co-workers getting a color TV very cheap from a dealer because it had a similar problem, so I guess way back it wasn't uncommon to have issues like that.
Can I do that with a motor
YOu mean use its fields to degauss things? Yes. But the fields are usually well confined so nott great. But - here is a trick I once used. Remove the rotor and side from a standard small induction motor. Disconnect the starter winding. Use a 12V AC transformer to power it - I used an old battery charger with the rectifiers removed. Now turn in on and slowly mover something - maybe a jar of nails in and out. And do it carefully enough and they are demagnetized!
Degaussing coil.
Exactly!
Heating a magnet with a torch will also demagnetized it.
Yes! The critical temperature is the Curie temperature which can vary quite a bit from material to material. Also works the other way - heating something up and let it cool in a magnetic field and will become magnetized.
please tell me how to DE-magnetize myself . they poisoned me now im magnetized . im hoing to die otherwise