Hello, ive been looking into the gray tube for a while now. But i have some problems figuring out how to chop the power on the high voltage side.
I have made a device that sort of looks like one, but the circuit is still far from where it needs to be. scrapheap EV Gray tube
It sends a pulse(20 -30 kHz) into a TV-transformer, and whatever comes out goes to the tube. I need to chop AFTER the transformer.

Anyway, I'm trying to figure out how to do that, normal transistors burn out at a few hundreds of volts at best. So now i found this new component that might be able to do it, called a thyristor (SCR). Of wich i know little about and have little knowlege of its characteristics in this matter.
My plan was to have a 4kV power supply with a good capacitor for starters, and then through switching action of the thyristor discharging into the tube. The thyristor i want to control with a 555 timer and a small mosfet. Because I read that thyristors work on current, and 555's don't do current.

Would anyone care to explain me whether this is a viable construction? Or maybe i would be better off with a vacuum tube of some sort. Also do i need to use two 555 timers, so i can control the duty cycle?

Sorry if this sounds as a n00b question, I'm still learning :P

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Well, 555 timer is a hoax.I won't work IMHO The only one which works with tubes is perfect sinewave I believe

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I"m not sure what you mean that the 555 timer circuit is a hoax. I have worked in electronics most of my life and every 555 timer circuit I have seen works just like it was designed to. As far as vacuum tubes go they will accept any kind of signal you send to them. They make excellent switches and can be turned on and off with a square wave signal even faster than most solid state components. The biggest problem with tubes are that you will need a filament supply and tubes are getting harder and harder to find. As far as the SCR goes the problem with using it as a switch is that once it is turned on it will not turn off until the voltage is gone. if you intend to leave it on until your capacitor is totally discharged then it will work for what you want.

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Hmmmm. interesting, i knew this wasn't going to be easy.

I read that the scr only remains open as long as current is flowing. I can't really predict the amount of current that will be flowing but it shouldn't be much, especially with these short pulses current should always be one step behind, right?
If I would be able to construct it in such a way that the current never exceeds the thyristors' threshold, it shouldn't be a problem.
Please correct me if I'm wrong though, I didn't go to school for this.
Another option would be to use a very small capacitor so that when it empties itself, that time would be equivalent to the discharge time we want.

I know tubes are hard to find these days, pretty much the only market left is the audiophile market, and I don't think those tubes will be able to handle the voltages required.

thanks for replying guys.

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I don't say that I know anything, just reading carefully answers I think that square wave is EXTREMALLY hard to produce required effects, especially not perfect wave.For example Stanley Meyer needed PLC circuit to continously follow resonance frequency.Perfect rectified sinewave would be simpler to use I guess.

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I think i found the part I need for successful switching. While watching a lecture by mr. lindemann. He talked about these pancake coils used to light bulbs with one wire.
The switching action was done by a Hydrogen thyratron.
Thyratron - Wikipedia, the free encyclopedia
So there you have it, now all i need to do is find one

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Hi Jan , My name is Jacqui , I see that there is problem to find a high speed high voltage switch for this gray device . I tried to obtain a hydrogen thyratron and ran into a host of difficulties with suppliers , not to mention the prices of such devices . I wonder if anyone knows of another way to achieve a switch with suitable capabilities .
Regards Jacqui .

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mechanical switching. Unless you know your electronic components mechanical switching via a commutator is probably the best way to go. There are some Mosfets and IGBT's rated for high voltage.

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Would you have any names of those mosfets or igbt's? I recently searched alldatasheet.com for suitable transistors, but not one of them got even close.
Yes maybe mechanical, but that also has a lot of problems that go with it.
The reason i'd like to do this in a solid state way is so that it's really easy to play with diffrent intervals, dutycycles etc. Because my guts tell me this is going to take a lot of tuning. Turning a pot is easier than cutting a new commutator wheel. And the frequencies i'd like to try are also a bit out of the mechanical range

Jacqui:
Could you describe those difficulties? And give an indication of prices? Maybe i should look for some second hand one from an army dump or so.

Thanks for the input guys.

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What sort of voltage ratings are we talking about here Jan? You need to be careful with this stuff. Powerex Insulated Gate Bipolar Transistor (IGBT) Modules-including Trench Gate and HVIGBTs <-250v to 6500v IGBT's here. Or google HV IGBT. Ive never used one, but Id imagine they are similar to a transistor to connect. You would need to do your homework on setting one up and triggering it correctly. Ive been doing some experiments using a PWM circuit to fire a Fet and using it to pulse transformers to gain HV off the secondaries. Ignition coil works good for this and is cheap and easy to find. MOTs are ok too. If you want to chop power on the hv side then I would think it needs to be stored in a capacitor first, but this is when it gets dangerous if you're not careful. I can fill a 2000v 1uF cap to over a 1000v off 12v 200ma in about 2 seconds with a simple circuit. And it only takes one zap to get you in trouble from there.

Looking at your simple circuit I dont see much point in the bridge rectifier. One diode maybe, but not all four. You could put a cap here instead, with one diode going to the positive terminal. It would need to be a HV cap and HV diode of course, at least 2000v for both Id imagine, microwave cap is a good starting point, it usually has a bleed resistor integrated so that HV isnt stored for any length of time. Use an analogue gauge to monitor voltage build up in the cap, and keep your hands away from the terminals until its safe. Dont assume that the cap is empty even if the gauge says it is.

Oh and by the way, mechanical can still be super easy, and cheap. You could do it with two bolts

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Thanks ren!
I will look into those igbt's 6500V is good enough. At least its a whole lot better than a 600$ thyratron I will look into the rise time characteristics to see if they will suit the application. I don't know if you've looked into this kind of energy generation, but the switch needs to be very abrupt and short. There's this lecture by mr Lindemann on some kind of conference. Where he reads from secrets of cold war technology, and where he links tesla's experiments with the gray tube. Very interesting to listen to.
Also the main reason i want to switch on the HV side is so i can charge a big cap (as you mention). If i pulse on the low voltage side the cap allows me no control on the sparks that are generated, so that's why.

As far as the dangers go, i'm pretty well informed on the dangers. when you start charging big caps with HV it gets deadly. So don't worry, i will insulate and shield.

And the diagram in the other topic you can also forget. I am planning to do the next machine with one or two MOT's (as you mentioned)

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