CRT into HV cap?
King_of_Junk, Sun Aug 20 2006, 08:16PMI've heard of making a CRT into a high voltage capacitor, but there is little to be found on the exact method. I thought you were to do something like put aluminium foil over the screen and use the regular connection for the flyback, but rather than haphazardly experiment I'd like some info. Anyone know anything- sites or anything- about using CRTs as caps?
I was planning on using one or more as the caps in a flyback driven tesla coil. Please notify me if this is unwise.
Re: CRT into HV cap?
Marko, Sun Aug 20 2006, 09:10PM
It's pretty bulky, low capacitance and leaded glass is probably even more lossy than 'normal' colorless glass.
Simple bottle caps are much less silly idea. ANd they won't implode if you drop them.
Marko, Sun Aug 20 2006, 09:10PM
It's pretty bulky, low capacitance and leaded glass is probably even more lossy than 'normal' colorless glass.
Simple bottle caps are much less silly idea. ANd they won't implode if you drop them.
Re: CRT into HV cap?
Bjørn, Mon Aug 21 2006, 12:46AM
The CRT is a capacitor, it has a conductive coating on the inside and outside. It is used to smooth the output from the flyback. The glass is thick so the capacitance is low but it is reliable at high voltages.
Bjørn, Mon Aug 21 2006, 12:46AM
The CRT is a capacitor, it has a conductive coating on the inside and outside. It is used to smooth the output from the flyback. The glass is thick so the capacitance is low but it is reliable at high voltages.
Re: CRT into HV cap?
benbradley, Mon Aug 21 2006, 02:21AM
The CRT is a capacitor, it has a conductive coating on the inside and outside. It is used to smooth the output from the flyback. The glass is thick so the capacitance is low but it is reliable at high voltages.
What is the application? If you need high current (as in a TC resonant capacitor) I have my doubts that it would work. The coating is, I think, carbon and somewhat resistive. It works fine for the high voltage and very low current the CRT uses, but the effective series resistance could be a problem for some applications.
benbradley, Mon Aug 21 2006, 02:21AM
The CRT is a capacitor, it has a conductive coating on the inside and outside. It is used to smooth the output from the flyback. The glass is thick so the capacitance is low but it is reliable at high voltages.
What is the application? If you need high current (as in a TC resonant capacitor) I have my doubts that it would work. The coating is, I think, carbon and somewhat resistive. It works fine for the high voltage and very low current the CRT uses, but the effective series resistance could be a problem for some applications.
Re: CRT into HV cap?
Terry Fritz, Mon Aug 21 2006, 10:18PM
Hi,
I used to fix TVs, prolly before you all were born
I don't even have a TV now 
But the picture tube forms a high voltage capacitor between the inside metal coating and the outside coating to filter and stabilize the HV from the flyback and recitifier. But the current there is very "low". Tesla coils like very "high" current. TV like 0.02Amp, Tesla coil like 500Amps(!!).
However, even DigiKey sells HV caps in the $25 to $75 range that are like a thousand times better: 445-2271-ND, 445-2266-ND, 445-2257-ND. Just search on ceramic caps at like 20, 30, 50 kV
)
But for a Tesla coil, we are talking hundreds of amps!!! You need "MMC" caps for that. Just google search on "MMC capacitor" and you will find them)
If it weren't for the lead, the old TV tube would be a fun shotgun taget
If you need "cheap" go with beer bottle caps....
Cheers,
Terry
Terry Fritz, Mon Aug 21 2006, 10:18PM
Hi,
I used to fix TVs, prolly before you all were born
I don't even have a TV now But the picture tube forms a high voltage capacitor between the inside metal coating and the outside coating to filter and stabilize the HV from the flyback and recitifier. But the current there is very "low". Tesla coils like very "high" current. TV like 0.02Amp, Tesla coil like 500Amps(!!).
However, even DigiKey sells HV caps in the $25 to $75 range that are like a thousand times better: 445-2271-ND, 445-2266-ND, 445-2257-ND. Just search on ceramic caps at like 20, 30, 50 kV
)But for a Tesla coil, we are talking hundreds of amps!!! You need "MMC" caps for that. Just google search on "MMC capacitor" and you will find them
)If it weren't for the lead, the old TV tube would be a fun shotgun taget
If you need "cheap" go with beer bottle caps....
Cheers,
Terry
Re: CRT into HV cap?
Dr. Drone, Mon Aug 21 2006, 11:50PM
Dr. Drone, Mon Aug 21 2006, 11:50PM
Re: CRT into HV cap?
Avalanche, Tue Aug 22 2006, 01:49AM
I second the bottle caps. I've run a successful mini TC from a flyback and the remains of a nights drinking! See my sig (shameless site plug :p )
Avalanche, Tue Aug 22 2006, 01:49AM
I second the bottle caps. I've run a successful mini TC from a flyback and the remains of a nights drinking! See my sig (shameless site plug :p )
Re: CRT into HV cap?
GODSFUSION, Tue Aug 22 2006, 04:51PM
Ive never used the CRTs as a capacitor simply for the reasons mentioned but since i diddent have access to Al sheets or well anything to use as an electrode i used the sheets of whatever they are used as the electron mask inside thre screen. I made two rolled caps and filled the cvap wth xfrmer oil to help fill the air gaps in the hols.
I wouldent suggest trying it though it is quite lossy and diddent hold a charge well over 4kv for more than a few seconds, i tried rolling the second tighter but it only upped to 7kv before dielectric breakdown after like a second.
Was a neat learning expereience though.
- Wayne -
GODSFUSION, Tue Aug 22 2006, 04:51PM
Ive never used the CRTs as a capacitor simply for the reasons mentioned but since i diddent have access to Al sheets or well anything to use as an electrode i used the sheets of whatever they are used as the electron mask inside thre screen. I made two rolled caps and filled the cvap wth xfrmer oil to help fill the air gaps in the hols.
I wouldent suggest trying it though it is quite lossy and diddent hold a charge well over 4kv for more than a few seconds, i tried rolling the second tighter but it only upped to 7kv before dielectric breakdown after like a second.
Was a neat learning expereience though.
- Wayne -
Re: CRT into HV cap?
King_of_Junk, Tue Aug 22 2006, 05:56PM
Thanks for all the help. I was going to use it in a flyback coil or something like that. I'm just trying to research for now.
So, any good bottle cap schematics out there?
King_of_Junk, Tue Aug 22 2006, 05:56PM
Thanks for all the help. I was going to use it in a flyback coil or something like that. I'm just trying to research for now.
So, any good bottle cap schematics out there?
Re: CRT into HV cap?
EDY19, Tue Aug 22 2006, 07:36PM
Bottle caps are really easy- do a search on google for a bottle capacitor, and lots of stuff will show up.
EDY19, Tue Aug 22 2006, 07:36PM
Bottle caps are really easy- do a search on google for a bottle capacitor, and lots of stuff will show up.
Re: CRT into HV cap?
King_of_Junk, Thu Aug 24 2006, 10:11PM
I've seen them, but I was just wondering if anyone had some "favorite" schematics or something like that. I just don't think google turns up the best things at the top of the list.
But I'll definitely look.
King_of_Junk, Thu Aug 24 2006, 10:11PM
I've seen them, but I was just wondering if anyone had some "favorite" schematics or something like that. I just don't think google turns up the best things at the top of the list.
But I'll definitely look.
Re: CRT into HV cap?
Michael W., Thu Aug 24 2006, 10:35PM
For your viewing pleasure (can you believe it only took 60 seconds to draw? )
Michael W., Thu Aug 24 2006, 10:35PM
For your viewing pleasure (can you believe it only took 60 seconds to draw?
)
Re: CRT into HV cap?
King_of_Junk, Fri Aug 25 2006, 01:40AM
Grr... Thanks. I was gonna look in a while...
Ok, maybe I'm just lazy or something...
And aren't you supposed to keep them in a bucket of salt water or something?
Isn't using a CRT as a capacitor just cooler?
And some tubes are mighty hearty. I had a tube in the back of my truck- It was in the plastic case of the TV but the back was off and the circuit board was out- and I went around a corner and forgot the tailgate was down. It didn't break at all. It was about a 27 inch tube too. But it is still sitting in a ditch in Wylie by the road...
King_of_Junk, Fri Aug 25 2006, 01:40AM
Grr... Thanks. I was gonna look in a while...
Ok, maybe I'm just lazy or something...
And aren't you supposed to keep them in a bucket of salt water or something?
Isn't using a CRT as a capacitor just cooler?
And some tubes are mighty hearty. I had a tube in the back of my truck- It was in the plastic case of the TV but the back was off and the circuit board was out- and I went around a corner and forgot the tailgate was down. It didn't break at all. It was about a 27 inch tube too. But it is still sitting in a ditch in Wylie by the road...
Re: CRT into HV cap?
Michael W., Fri Aug 25 2006, 01:43AM
I just don't think the CRT Cap is practical....or robust enough to work....
Michael W., Fri Aug 25 2006, 01:43AM
I just don't think the CRT Cap is practical....or robust enough to work....
Re: CRT into HV cap?
King_of_Junk, Fri Aug 25 2006, 01:48AM
But it is cool
It's a vacuum tube. Not just a bottle of salt water.
Not practical, but cool...
King_of_Junk, Fri Aug 25 2006, 01:48AM
But it is cool
It's a vacuum tube. Not just a bottle of salt water.
Not practical, but cool...
Re: CRT into HV cap?
Avalanche, Fri Aug 25 2006, 02:22AM
It would be a lot cooler to have a working coil though, and use the CRT as a strike target. I think they glow if you get enough RF going through them, but I've never tried it.
For bottle cap construction details here's some good info and for a full schematic, just search google for 'spark gap tesla coil'.
Avalanche, Fri Aug 25 2006, 02:22AM
It would be a lot cooler to have a working coil though, and use the CRT as a strike target.
I think they glow if you get enough RF going through them, but I've never tried it.For bottle cap construction details here's some good info and for a full schematic, just search google for 'spark gap tesla coil'.
Re: CRT into HV cap?
Coronafix, Fri Aug 25 2006, 02:57AM
That's some good value bottle caps you got there Part Scavenger.
I only got half that in capacitance with a litre bottle.
I used a steel bolt and the foil wasn't anywhere as smooth as yours.
I might have to make some more and see what I can get.
Edit: Of course I just realized that the glass thickness has got everything to do with it.
How do they stand up to 15000V input, any idea?
Coronafix, Fri Aug 25 2006, 02:57AM
That's some good value bottle caps you got there Part Scavenger.
I only got half that in capacitance with a litre bottle.
I used a steel bolt and the foil wasn't anywhere as smooth as yours.
I might have to make some more and see what I can get.
Edit: Of course I just realized that the glass thickness has got everything to do with it.
How do they stand up to 15000V input, any idea?
Re: CRT into HV cap?
King_of_Junk, Fri Aug 25 2006, 03:03AM
Well, I've hit it with arcs from a flyback. It glows in the spot you hit it at for a couple seconds after you take it off. I'd want to do some damage to one if I hit it with a big streamer. Get some arc over or somehing. That would be pretty...
King_of_Junk, Fri Aug 25 2006, 03:03AM
Avalanche wrote ...
It would be a lot cooler to have a working coil though, and use the CRT as a strike target. I think they glow if you get enough RF going through them, but I've never tried it.
It would be a lot cooler to have a working coil though, and use the CRT as a strike target.
I think they glow if you get enough RF going through them, but I've never tried it.Well, I've hit it with arcs from a flyback. It glows in the spot you hit it at for a couple seconds after you take it off. I'd want to do some damage to one if I hit it with a big streamer. Get some arc over or somehing. That would be pretty...
Re: CRT into HV cap?
Part Scavenger, Fri Aug 25 2006, 12:12PM
Thanks! They'll do better if you cover them in electrical tape I hear (not at leaky), but they don't look as cool anymore. My glass is approx 1/8 thick in the tutorial.
As for volt rating, I've only ever had one fail, but it had a crack I didn't know about. (pic of it is at the bottom of my SGTC page) I've put like 30kV even in a thin-glassed one, and nothing happened. As for hitting a CRT with a TC, it's rather underwhelming. The screen glows a little bit. The racing arcs that travel all over the back of the CRT look cooler. I've got some pics at home.
Flybacks (even in series) are just fine. Worst thing that can happen is you lose some aluminum foil and a beer bottle...
Part Scavenger, Fri Aug 25 2006, 12:12PM
Thanks! They'll do better if you cover them in electrical tape I hear (not at leaky), but they don't look as cool anymore. My glass is approx 1/8 thick in the tutorial.
As for volt rating, I've only ever had one fail, but it had a crack I didn't know about. (pic of it is at the bottom of my SGTC page) I've put like 30kV even in a thin-glassed one, and nothing happened. As for hitting a CRT with a TC, it's rather underwhelming. The screen glows a little bit. The racing arcs that travel all over the back of the CRT look cooler. I've got some pics at home.
Flybacks (even in series) are just fine. Worst thing that can happen is you lose some aluminum foil and a beer bottle...
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