Electron gun- what's wrong here?

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David Kunkle
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Re: Electron gun- what's wrong here?

Post by David Kunkle »

Rex Allers wrote:Since, in my last post, I talked about removing or bypassing the caps in the output of the inverter, I thought I would comment about Steven's circuit. His configuration, with two diode strings, is a voltage doubler. In this case the two caps on the inverter are put in parallel as the charge storage for the first stage of the doubler. That's a valid approach and doesn't require any hacking on the inverter board.

Steven also mentions using fast diodes, but the 1N4007's in his schematic aren't particularly fast; about 2 uS trr, I think. For this kind of application I ordered some surface mount BYG23M diodes from Mouser, a while back. They are spec'ed at 1 KV, 1.5A, 75 nS trr. Overkill on the current for this but pretty cheap, if I remember right. Maybe others have recommended part numbers to look for.
Rex,

The 5V will be coming from an adjustable supply. Be interesting to see how much I can vary the output. Good tip.

I have found 1KV, 1A fast switch diodes on ebay with trr of 500ns. 4 for about $15 incl. shipping.

You're right about the grounds being connected. I found the jumper between the 2 grounds. What would be the advantage to disconnecting these?

Thanks.
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Re: Electron gun- what's wrong here?

Post by Steven Sesselmann »

David,

The capacitor should be around 10 nF and yes another one will smooth the ripple, but for your purpose ripple is not an issue.

One more thing I should have mentioned above is that you need to turn the diodes the other way, because you obviously want negative bias on your filament.

These inverters are not going to supply much current, but since you are heating the filament you just need some negative bias on the filament to make it become an electron emitter, this rather weak electron emitter should generate enough ions to keep the fusor lit up at low pressure.

Good suggestion from Rex to put a potentiometer on the input, so you can control the bias on the filament.

Steven
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Re: Electron gun- what's wrong here?

Post by David Kunkle »

So you can make it + or - bias just by turning the diodes around?

According to this: http://dkc3.digikey.com/PDF/CA2011/P2792.pdf , pink column, digi-key part # 445-1621-ND , the output is about 10mA if both outputs are wired together?

On that same pdf, same page, I see the largest (V-wise) inverter outputs 2100V. If my 900V inverter will hit 1400V, would that 2100V inverter wind up putting out about 3200V if I needed more electrons or would it just run out of mA being used up through beam current?

Thanks again.
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Re: Electron gun- what's wrong here?

Post by Rex Allers »

David, there's no reason in this application to float the HV ground. I just mentioned it to be complete. I think I had a reason once, but I can't remember why now. Maybe monitoring current out.

Those diodes you mentioned seem very expensive. Also, 500 nS isn't real fast as "fast diodes" go.

You can do much better buying new direct from Mouser.com, probably Digikey too but I didn't check there. I looked at mouser for those BYG23M that I bought earlier. I bought 100 when I ordered. Looks like the price for 100 now would be $16.90. Those are smd package. A standard fast axial diode is UF4007; 100 of them is less, $10.20 for the first Fairchild listing.

Both of these diodes are 1KV, 1A, 75nS. You can order smaller quantities but the price goes up a little. Still way better than the ones you found. If you have time to kill, you could try the parametric search at mouser or digikey. There may be something similar with 2KV rating or etc.

Edit: I forgot to mention, yes, you can switch all the rectifier diodes around to change the polarity of the output.
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Re: Electron gun- what's wrong here?

Post by David Kunkle »

Just got the proper diodes from Mouser. Got 6 for 45 cents each- then there's the $8 for shipping.
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Re: Electron gun- what's wrong here?

Post by Steven Sesselmann »

David,

Plenty on ebay if you dont mind waiting for them, just search for "8kv rectifier diode"

http://www.ebay.com/itm/20-x-30mA-8kV-1 ... SwcF9UXGpR

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Re: Electron gun- what's wrong here?

Post by Rex Allers »

Steven and Dave,

I've had good results with that ebay seller 'high-voltage-hv' too. I've bought a number of hv diodes, those blue ceramic hv caps, and some hv wire from them. No complaints so far. Check out their 'store' or 'see other items' on ebay.

Outside of ebay, the site hvstuff.com seems pretty good too.
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Re: Electron gun- what's wrong here?

Post by Jeroen Vriesman »

I don't really get the idea of a high negative bias on the filament.

Indeed, it would accelerate the electrons more, but imho this might be the problem, not the solution, and the negative power supply would just be used for running current through the diode (filament + anode ring = diode).

If you take a look at the field strength between the filament and the anode ring, and compare that with the field strength between the anode ring and the final target:

if the distance between the filament and the anode ring is about 4mm (estimated from the photo), the field strength will be 320/4E-3 = 80 kV/m.
That means, if you want any substantial electron yield, the field strength between the anode ring and the target must be stronger than 80 kV/m near the center of the ring!

What I would do:

increase the distance between the filament and the anode ring a bit, give the target a high positive potential (e.g. 10 kV), make the voltage on the anode ring variable.

Now start with 0V (with respect to the filament) on the anode ring, measure current on the target, you should be able to make the current on the target zero by making the voltage on the ring a bit negative (a few volts), just like a triode.

Then slowly increase the voltage on the ring, a current on the target will flow, you will see that there is a maximum met the voltage on the ring is a bit positive, but when it gets too positive all electrons will go directly from the filament to the ring and not to the target.
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Re: Electron gun- what's wrong here?

Post by Steven Sesselmann »

Jeroen Vriesman wrote:I don't really get the idea of a high negative bias on the filament.

Indeed, it would accelerate the electrons more, but imho this might be the problem, not the solution, and the negative power supply would just be used for running current through the diode (filament + anode ring = diode).!
.
Jeroen, the idea behind a negatively biased ion source is to accelerate the electron more which means accelerating the positive ion less, Preferably we want the deuterium nucleus to stand still, and we can in fact achieve that by ionising it at -62 kV, but the world of fusioneers still believe in building atom smashers to overcome the imaginary Coulomb force, which is why they are still trying after more than 60 years.

Unfortunately the little CCFL inverter won't be able to deliver much current, so the negative bias will fall off as the current goes up, I used a rectified MOT in my ion sources, but that becomes a bit more dangerous.

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Re: Electron gun- what's wrong here?

Post by Jeroen Vriesman »

Hi Steven,

I just tried to answer the original question about an electron source, not the ion source related stuff.

The filament-anode ring-target setup is comparable to a ordinary triode (cathode-grid-anode) with well-known behaviour.
Making the grid in a triode positive a little bit gives more anode current, but make it too positive and the current will only flow between the cathode and the grid (and it will burn the grid in a regular triode).

The absolute potential of the entire setup doesn't make any difference, and having a large potential difference between the filament and the anode ring just draws maximum current between them (limited by emission, space charge or supply current) . Having the filament and the anode ring both biased with an negative potential is the same as have a higher positive potential on the target, but with the side effect that the chamber walls are positive with respect to the electron source, this will pull the electrons to the walls of the chamber.

I've seen these effects with the emission measurements of my thoriated tungsten wire activation experiments, something with the coulomb force I guess.
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Re: Electron gun- what's wrong here?

Post by Steven Sesselmann »

Jeroen,

Yes, it will behave like a triode, however it is not irrelevant at what potential an atom becomes ionised, and in a fusor you will get more fusion when you create low potential ions. The way to do this is exactly as David is doing, one could go a step further and lower both the ring and the filament together, making sure there is enough differential to generate a stream of electrons.

As for the Coulomb force and the gravitational force for that matter, have you ever seen either?

I would be most surprised if you said yes, because I have never heard of anyone observing any of the four fundamental forces we are being taught about, the fact is we observe constant or accelerating velocity and so as to not look like idiots, the so called educated people gave it a fancy name like "Coulomb Force", "Gravity" etc. and those who were not so smart bought it.

Unicorns that's all they are, and the sooner you spot them the sooner they gallop away..

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Re: Electron gun- what's wrong here?

Post by David Kunkle »

Jeroen Vriesman wrote: Having the filament and the anode ring both biased with an negative potential is the same as have a higher positive potential on the target, but with the side effect that the chamber walls are positive with respect to the electron source, this will pull the electrons to the walls of the chamber.
I understand that the chamber walls and nipple the electron source is contained in would be positive w/ respect to the negatively biased source. But with Gauss' Law, wouldn't there be zero E field inside the nipple and the spherical chamber to pull the electrons to the walls? Or is it really just a matter of the negative fields pushing the electrons away, and some of the electrons just happen to find their way to the walls which then simply go to ground?
If your experiment needs statistics, you ought to have done a better experiment.

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Re: Electron gun- what's wrong here?

Post by Steven Sesselmann »

Having the filament and the anode ring both biased with an negative potential is the same as have a higher positive potential on the target
This statement which is widely believed to be true is a false statement. I think I have a reasonable argument for absolute potential and for the statement above to hold true, potential would have to be scalar. A particles velocity appears as a function of it's potential with respect to the observer, so yes Schroedinger was right, it does depend on who is looking.

Steven

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Re: Electron gun- what's wrong here?

Post by Jeroen Vriesman »

Hi david,
But with Gauss' Law, wouldn't there be zero E field inside the nipple and the spherical chamber to pull the electrons to the walls?
Yes, but only if there are no objects in the chamber with some other potential. If you have something inside your chamber at a potential U, and the chamber is grounded, the electric field is about U/d (the shape of the field can be much more complicated, U/d is just an indication) where d is the distance between the object and the wall.

In my experiments involving emission I have to make the filament a bit positive to avoid all the emission current running between the filament and the chamber walls.
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Re: Electron gun- what's wrong here?

Post by Jeroen Vriesman »

Hi Steven,

in your reference you seem to state that potential is limited because relative velocity is limited, however, the energy associated with relative velocity is not limited, it goes to infinity near the speed of light, so the potential is not limited. You are using the special theory of relativity in one argument, but you skip it for the conclusion.

There is some truth in force being an illusion, Newton already knew that his theory of gravity was problematic, it introduced a "mysterious force working at a distance".
However, the problem is not physical, it's a psychological problem, the idea that some kind of "contact" is needed for a "force" is just a result of our size and the way humans experience the world. All "forces" work at a distance, when we push things around there is not a single molecule actually touching another molecule.

What's happening is that the phenomenon we call "force" is just the first derivative of the total energy of the system, we just exchange forms of energy, gravitational, electrical, thermodynamic energy etc.
When we push against a wall it just means that we do not shift enough energy from one place to another to push our hands through the wall, "contact" just means "not having enough energy to change the state of the matter involved".

This insight leads to some very useful mechanical methods, called the Hamiltonian and Lagrangian, https://en.wikipedia.org/wiki/Hamiltonian_mechanics

So there is just the potential of the system. Thermodynamics show us that states which can be solely described by information theory still represent an energy, so the whole thing can be modelled as information only. Attempts at modelling gravity that way have recently been made by Verlinde https://en.wikipedia.org/wiki/Entropic_gravity

So indeed, "force" can be considered less fundamental than potential, but potential is not limited by the speed of light, since the energy needed to reach the speed of light goes to infinity.

In physics the EM theory is considered a "gauge" theory, the potential of the system as a whole can be varied without changes in behaviour.
Only by assuming the entire universe does not have a net charge one could define the absolute zero potential. (the idea that the potential at infinity is 0)

That force (and even the derived concept of a "field") are less fundamental than potential is experimentally proved by the Aharonov-Bohm experiment https://en.wikipedia.org/wiki/Aharonov% ... ohm_effect, a wonderful experiment!

As for your "second case for absolute potential"... seems to me a case of "not even wrong". Choosing the proton is arbitrary (if you take a charmed lambda or sigma particle you get different "absolute maximum" potential), equating the equivalent energy to surface potential, stating that a collection of protons has the same surface potential as a single proton (without even defining the "surface" of the charge collection)? Strange stuff.
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Re: Electron gun- what's wrong here?

Post by Steven Sesselmann »

Jeroen Vriesman wrote:Hi Steven, in your reference you seem to state that potential is limited because relative velocity is limited, however, the energy associated with relative velocity is not limited, it goes to infinity near the speed of light, so the potential is not limited. You are using the special theory of relativity in one argument, but you skip it for the conclusion.
Jeroen, you make an important observation, because in my paper I talk about "potential" not "potential energy", the two terms are often confused. When you divide potential energy i.e electron-volts by electrons you just get Volts and the unit Volt is a measure of raw potential and it has to be limited.
Jeroen Vriesman wrote:There is some truth in force being an illusion, Newton already knew that his theory of gravity was problematic, it introduced a "mysterious force working at a distance".
However, the problem is not physical, it's a psychological problem, the idea that some kind of "contact" is needed for a "force" is just a result of our size and the way humans experience the world. All "forces" work at a distance, when we push things around there is not a single molecule actually touching another molecule.
Correct, I agree and we need to keep in mind that the terms forces and fields are mathematical constructs of the mind which have no physical reality, but help us calculate the velocity, which is really all I am saying in my paper, that the term potential refers to velocity or change of velocity.
Jeroen Vriesman wrote:What's happening is that the phenomenon we call "force" is just the first derivative of the total energy of the system, we just exchange forms of energy, gravitational, electrical, thermodynamic energy etc. When we push against a wall it just means that we do not shift enough energy from one place to another to push our hands through the wall, "contact" just means "not having enough energy to change the state of the matter involved". This insight leads to some very useful mechanical methods, called the Hamiltonian and Lagrangian, https://en.wikipedia.org/wiki/Hamiltonian_mechanics
Agree..
Jeroen Vriesman wrote:So there is just the potential of the system. Thermodynamics show us that states which can be solely described by information theory still represent an energy, so the whole thing can be modelled as information only. Attempts at modelling gravity that way have recently been made by Verlinde https://en.wikipedia.org/wiki/Entropic_gravity
So indeed, "force" can be considered less fundamental than potential, but potential is not limited by the speed of light, since the energy needed to reach the speed of light goes to infinity.
I would agree, force is less fundamental than potential and potential is less fundamental than velocity, because velocity is what we actually observe, so why is it so hard to see that potential is limited when we ultimately measure potential in velocity?
Jeroen Vriesman wrote:In physics the EM theory is considered a "gauge" theory, the potential of the system as a whole can be varied without changes in behaviour.
Only by assuming the entire universe does not have a net charge one could define the absolute zero potential. (the idea that the potential at infinity is 0)
This is where my ground potential theory diverges from the standard model, because the term you used above "entire universe" implies that we somehow act out our lives in a domain called the universe, I see this concept as fundamentally flawed. In GPT the observer is floating at ground potential and by manipulating it's own potential it changes the relative universe. I came to this conclusion because the GPT equation which relates the mass of the electron to ground potential is non local, i.e. when you as the observer climb a set of stairs, you increase your absolute potential which reduces the mass of an electron everywhere, so you are basically turning back the clock of your whole Universe not just your own clock. Think carefully about this.

It is also an outcome of the theory that space everywhere is at ground potential, this means our current understanding that looking out into the universe is equivalent of looking back in time is wrong. What we see when we look out into space is NOW on the absolute time scale, we see the sun as it is now and we see the moon as it is now. True light travels at a finite speed, so if we see the moon as it is now, then it's also in our future as we see it. So the light cone changes shape.
Jeroen Vriesman wrote:That force (and even the derived concept of a "field") are less fundamental than potential is experimentally proved by the Aharonov-Bohm experiment https://en.wikipedia.org/wiki/Aharonov% ... ohm_effect, a wonderful experiment!
Skim read it, but it's not something I can understand in reading it once, my initial reaction was that the experiment is flawed because it's measuring the velocity relative to the local fields and ignoring the observer, this is the general trend with quantum experiments and the reason why everyone is puzzled about quantum behaviour, they forget to consider the observer. When three people stand around the box containing Schroedingers cat, there are three observers and three realities, and not one realitry because there is one box and one cat.

Jeroen Vriesman wrote:As for your "second case for absolute potential"... seems to me a case of "not even wrong". Choosing the proton is arbitrary (if you take a charmed lambda or sigma particle you get different "absolute maximum" potential), equating the equivalent energy to surface potential, stating that a collection of protons has the same surface potential as a single proton (without even defining the "surface" of the charge collection)? Strange stuff.
Protons are a pretty good candidate, I have always been fascinated about protons, where they come from and why they are all identical, as a manufacturer I envisage some machine mass producing these particles that make up 99.945% of everything. They also happen to be the most energy dense naturally occurring particle, number one on the table of isotopes, which is why I chose the proton as the upper limit to potential. if there was another particle heavier and denser it would sit above and before Hydrogen on the table of elements, but noop I doubt you will find any stable particle up there.

938 million volts is just another way to express the speed of light c, the only reason the units are different is because we have messed up the units. So to normalise the units in GPT I simply multiply the speed of light by the fraction of absolute potential, and I can find the velocity of any particle with this simple equation.

∆v = c(∆U/Ø)

You can also write it like

∆v = ∆U (c/Ø)

Where c/Ø simply fixes up our stuff up of the units and ∆v = ∆U simply says velocity is exactly the same as potential.

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Re: Electron gun- what's wrong here?

Post by Dennis P Brown »

A quick edit error: You say
When you divide potential energy i.e electron-volts by electrons you just get Volts ...
and of course, the unit of electron-volt cannot be divided by electron to produce a volt. The unit is named electron-volt. One does not divide equations by a physical material but only by numbers or numbers with units.
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Re: Electron gun- what's wrong here?

Post by Dennis P Brown »

Another point; you say
protons make up 99.945% of everything
. You are forgetting neutrons.

Also, protons may or may not be stable - one may assume it is but that isn't the same as it being one; so why not use neutrons for your potential since these are heavier than protons and are very stable when bound with a proton. In fact, some table of the elements use the neutron ... .
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Re: Electron gun- what's wrong here?

Post by Richard Hull »

What began here as a failed electron gun project has devolved or evolved, your choice, into a theoretical discussion. Let's stay on topic in this thread.

I suggest another forum and a new thread if some wish to continue this offshoot.

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Re: Electron gun- what's wrong here?

Post by David Kunkle »

I put the circuit together with all the right parts. Feeding it 5V DC, the HV probe initially shows 4-500V (occasionally catch it at around 1kv with an initial power on), but it would quickly fall to around 300V. And repeat each time I cycle it on and off. With just the circuit board minus diodes and caps, etc., I measure only 43V AC on each of the 2 outputs. When it measured only 43V on the HV probe, I tried just hooking up the DMM to it, but it flips out and goes blank. Not what it's supposed to be doing. Could it have been damaged when I had it mis-wired with the microwave diodes?
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Re: Electron gun- what's wrong here?

Post by Steven Sesselmann »

David, you should be measuring lower than -1000V after its rectified, and after the load resistor. Your DVM may not like voltages over 1000V and I wouldn't try measuring the 30 kHz AC side.

For this kind of measuring it's a good idea to make yourself a 1/1000 divider with a 1G/1M resistor, so 1V = 1000V

PS: Can you draw the circuit please.

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Re: Electron gun- what's wrong here?

Post by David Kunkle »

Apart from occasionally going over 600V, I see now why the DMM wouldn't like it- 60 Hz vs 30kHz. My HV probe output is divided by 1000 already.
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Re: Electron gun- what's wrong here?

Post by Dennis P Brown »

HV probes work terribly in that low end range; while hand held multi-meters just tend to fail in that same range since it (due to various factors) tend to read lower voltages than the actual voltage, which quickly exceeds the rate level of the meter causing it to fail.

Why not just make your own divider as Steve said (two cheap, low power resistors and that's it - his example works fine) for the multi-meter? So very simple - just design the range for the the high end being 2000 volt range and you are both safe and handle this grey area that doesn't have a good easy to buy solution relative to hardware.
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Re: Electron gun- what's wrong here?

Post by Rex Allers »

[Arrgh. I guess I flubbed submit. Second try on whole post.]

David,
I'm not sure what is going wrong but I do see one problem. For the output voltage this TDK CCFL supply can make, a single 1 KV diode is too low a voltage rating.

Rather than doing a lot of speculation, I decided to test. As I mentioned in an earlier post, I have a TDK CCFL module that looks like yours. A while ago I was doing some testing on a different supply and had the prototype I used with a simple rectifier and a divider for measurement. I reconfigured to attach that output to the TDK. Here are pic of what I used.
TDK CCFL with rectifier. Original test supply greyed out for clarity.
TDK CCFL with rectifier. Original test supply greyed out for clarity.
TDK test circuit. Simple rectifier and measurement voltage divider.
TDK test circuit. Simple rectifier and measurement voltage divider.
In the circuit diagram, on the left, I have shown the TDK module with its basic output circuit. I have bypassed the two caps by connecting to point 'A' to take the output directly from the transformer. On the right is my voltage divider for measurement. The main dropping resistance is 300 M ohm (three 100 M ohm resistors in series). The output is measured by a DMM across ~300 K ohm. Earlier, I had calibrated this ~300K value to give near exact 1 V out for 1 KV HV, or divide by 1000.

Testing the circuit with +5 VDC into the TDK module, I measured 1.26 V, so 1.26 KV output. I got about 1 KV out with about 4 V in. Therefore the 1 KV rating on your diode is probably exceeded a good bit. The diode I used is rated for 10 KV which is overkill in this circuit and probably drops the HV out a bit below what it could be.

The circuit you used is a voltage doubler which uses the caps on the TDK board. To verify it works the way I expected, I reconfigured the circuit and added a second diode to match your circuit. Here it is.
TDK test with voltage doubler.
TDK test with voltage doubler.
It did work as expected and with 5V in, I measured 2.5 V or 2.5 KV out.

So I'm not sure if exceeding the rating of 1 KV for your diodes by 26% is enough to kill them or not. For each of the diodes in your circuit you should be using two 1KV diodes in series.

In your last post you mentioned frequency. Some notes I have from earlier say this TDK supply probably runs the transformer at about 50 kHz, but that shouldn't matter. The caps in either of these circuits should filter out most of that to effective DC on the output.

It wouldn't surprise me if there is someting going wrong with the probe you are using to measure, too. In the last posts you haven't said much about what it is and I didn't go back to look if you covered that earlier. Do you know what its input resistance is? For not overloading this small supply, it should probably be at least 100 M and higher is better. My divider in this test is about 300 M.

You didn't say anything about how you constructed the circuit, either. I built this test by soldering "flying" components above a ground plane. This isn't the kind of voltage and frequency to try with one of those white plastic pluggable prototyping boards.

So as I have shown, it should work. I hope something here gives you a hint why it isn't working for you.
Rex Allers
David Kunkle
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Joined: Thu Apr 17, 2014 12:43 pm
Real name: David Kunkle

Re: Electron gun- what's wrong here?

Post by David Kunkle »

Thanks for all the info everyone. Thanks for going to all that trouble, Rex.

Probe info: 1-40 kV DC, divider ratio 1000:1, input resistance 1000 M Ohms- nominal. Also checked it against my main HV PS and its meter. In good agreement from 200 to 3 kV. (Hard to adjust it below 200V.)

Seemed the easiest route to try first was what Rex suggested. I re-wired it with 4 unused diodes. (Happen to have bought 6 total.) 2 diodes in series in place of each one. This time I got a max of 1800V, but it drops steadily until about 3-400V in a matter of seconds when I'm measuring it with the probe, and then stays there even after I remove the probe, "let it rest", and test it again- until I cycle the power to the inverter.
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford
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