Gray Tube Replication

[mlurye]

@Electrotek: Did you built your rotary spark gap? If you did, could you post picture of it?
I'm planning to build one too. Getting parts for it on e-Bay.

[lighty]

6 the Capacitors on the HV side must not discharge completely, power supply must have sufficient potential to maintain the HV during the discharge of the spark in the CSET.

My guess would be that if the discharging process is short enough and cut before capacitor voltage levels below certain values it would significantly reduce impulse ringing thus reducing the polarity change of the impulse to the minimum. It would in effect produce much cleaner DC impulse without much of AC component.

[boguslaw]

Fortunately power supply could be just working at 6kHz. The higher frequency the better and faster charging of capacitor 16. But there is also overshoot protection device which is really a back path to recharge capacitor 16 from radiant energy almost immediately (HF Mhz range or above).

That is compliant with Gray small system description which states that system has got final power after around 30 seconds.

[Electrotek]

@Electrotek: Did you built your rotary spark gap? If you did, could you post picture of it?
I'm planning to build one too. Getting parts for it on e-Bay.

Here's a non-updated picture:


I've since replaced the battery with a door bell transformer. The motor came from a hand held hair dryer, which uses a diode and the voltage drop of the heating element to provide 12V. to the motor. The disc came from a CD Rom drive.

When I tested this unit, the HV spark jumped to the motor and the mains ground, through the transformer.

I'm going to reconfigure this device. The two bolts will be connected and the lower electrode will be moved to the opposite side, on the top. A little silicone around the bottom of the bolts will hopefully prevent arcing to the motor. Otherwise, I'll have to use a larger platter, such as a CD disc.

I'll post a new picture when I change the setup and test it. Right now, I'm working on etching a spiral coil from aluminum foil.

[lighty]

@Electrotek

You're of course aware that due to the ionization around sparks you will end up with high current long arcs and premature sparking (especially at high speed that you need to achieve short impulses)? You will have to find a way to get rid of ionized air either through forced airflow or through enclosing the rotary sparkgap in high pressure inert gas chamber (or in the high vacuum enclosure). You might consider using dielectric disk with openings rather than exposed contacts- that will help reduce arcing to some degree.

Also, it is impossible to achieve microsecond range with any kind of mechanical device. Consider this- if we're talking about 1us impulses that would be equivalent of 1MHz. A disk with, for example, 10 contacts would have to trigger about 1'000'000 times/sec. That means 1'000'000 / 10 = 100'000 rev/sec. If you calculate this it translates into 100'000 rev/sec x 60 = 6'000'000 RPM.

Even with the best constructed mercury interrupters one can hardly expect to achieve even kHz range, let alone MHz.

[Electrotek]

Thanks for the tips, lighty. I am aware of the expected arc stretching, and I'm willing to tolerate this at first, to see if any Chernetski effects appear. This isn't too probable, since I expect the arc still won't be long enough. After that, I think I'll try your low pressure suggestion, if it appears something like this is needed.

The interrupter which powers the CSET isn't expected to produce micro second pulses. That's what the CSET does. When a cap is dumped across the Tube, the crossed field switch effect, when quenched, only allows a very short pulse in the capacitor's circuit. Especially when this discharge is expanded to a large volume within the Tube, providing a much lower impedance path. This will happen even if the CSET arc - between rods - is running constantly between cap discharges which are coming through an even slower motor commutator.

[What The Flux]

Pulses

What the Flux,

What I found is even with a very slow trigger contact speed, the cap is still forced to discharge fast so it is independent of the trigger contact speed.

The interrupter which powers the CSET isn't expected to produce micro second pulses. That's what the CSET does. When a cap is dumped across the Tube, the crossed field switch effect, when quenched, only allows a very short pulse in the capacitor's circuit. Especially when this discharge is expanded to a large volume within the Tube, providing a much lower impedance path. This will happen even if the CSET arc - between rods - is running constantly between cap discharges which are coming through an even slower motor commutator.

I agree Aaron.
As I think this through, the contact duration seems less important.
What I think is critical is a fast leading edge on the pulse. A semiconductor that switches too slow will reverse bias diode 28 before it lets enough energy flow build up, and it won't 'slam' shut. (That's assuming we have semiconductors lying around that can switch 3KV.)

The mechanical rotor contact seems to be the way to go. I'm looking forward to the group's results with that.

If we agree that this is correct, and read freeukpower's posts, we should be able to see this effect on a one-shot basis. That's what I'd like to duplicate.

So far I have been unable to get a spark with the diode in place (backwards, as we agree it should be). Is 12V enough to forward bias a MO diode before hitting it with a spark? That was trying to hit it with an ignition coil pulse. Maybe I need a cleaner pulse? (Again, the rise time might not be fast enough... don't know, I don't have an HV scope.)

[lighty]

@Electrotek

I suggested either high pressure or high vacuum. Low pressure would lower breakthrough voltage of the dielectric.

As for the short impulses in the CSET- aside from the diode I don't see anything that would prevent arc formation and much longer relaxation times than you anticipate. There is nothing in the CSET to prevent high current arc forming- discharge wise it is but a normal sparkgap (aside from the diode). I don't see anything that would quench the discharge in this case. One could try using strong magnetic field between discharge points, fast air flow or pressurizing CSET to some higher pressure with some inert gas like nitrogen, one could even consider filling the space between electrodes with some liquid dielectric like transformer oil or some silicone oil derivates.

I could be wrong on this one but I have extensive experience with sparkgaps both static and rotary and I empolyed everyting from magnetic quenching to forced air flow and high pressure inert gas- I even employed circulated liquid dielectric as a way of quenching. Again- there is nothing magical about CSET regarding it's sparkgap part- the only things that I could see possibly affecting it's performance is the introduction of carbon resistor, diode to prevent formation of arc but allow for a brief moment of spark formation (hopefuly without previous formation of streamers) and grid. As for the resistor I don't see anything special in employing carbon as material- it's just that any other resistive material would probably be in the form of resistive wire that would have to be wound thus introducing significant inductance and changing reactive component of overall impedance. Also, if carbon is placed close enough to the point of discharge it would probably heat up which would lead to higher resistance which could lenghten relaxation time of discharge and introduce self-regulation of current passing through electrodes.

Of course, that's my educated theory based in some parts on my hands on experience. So far it seems freeukpower proved at least two major poiints- one needs as short DC impulses as possible with as little oscillation as possible and one needs appropriate powerfull spark quenching in order to achieve supposed CSET effect. He achieved both points to a certain extent by using ball bearing dropped from height in order to shorten the discharge (quite innovative idea- kudos to him) and by forming substantial vaccum between discharge electrodes in order to quench the spark. Good work freeukpower and quite innovative designs using available parts.

[lighty]

As I think this through, the contact duration seems less important.
What I think is critical is a fast leading edge on the pulse. A semiconductor that switches too slow will reverse bias diode 28 before it lets enough energy flow build up, and it won't 'slam' shut. (That's assuming we have semiconductors lying around that can switch 3KV.)

Fast leading edge on the pulse can be achieved by using any transistor no matter BJT, IGBT or MOSFET. The problem is that electrostatic charges will kill them very fast- either by overvoltage spikes or by triggering them erratically once their intrinsic capacitances get saturated.

I was reffering to microsecond impulses since Gray was reffering to them as well. The problem with mechanical switches is that they will introduce a significant ammount of oscillation during later phases of discharge when the energy stored in the capacitor gets depleted below the level needed to sustain constant current. The moment one gets oscillation one can hardly speak about DC impulse- it becomes a damped wave oscillation rather then pure DC. Is it possible to achieve supposed CSET operation with that kind of impulse? I don't think that ATM anybody here really knows for sure.

[nat1971a]

i didnt mention this the other day but i splashed out and bought some vacuum tubes same model as gary mcgratten but different part number as it was a bit cheaper but still expensive.

They arrived today from USA

Just need to find some time to peform some experiments

[Aaron]

battery-diode-spark

So far I have been unable to get a spark with the diode in place (backwards, as we agree it should be). Is 12V enough to forward bias a MO diode before hitting it with a spark? That was trying to hit it with an ignition coil pulse. Maybe I need a cleaner pulse? (Again, the rise time might not be fast enough... don't know, I don't have an HV scope.)

I have had no problem even using a 6v 1.7ah gel cell with the diode being a single 1000v 6amps rating and even a string of 15 of those diodes for 15kv, 6amp rating.

[Aaron]

coil resistor

it's just that any other resistive material would probably be in the form of resistive wire that would have to be wound thus introducing significant inductance and changing reactive component of overall impedance.

I have tried this as well and if too much, the HV cannot find ground jumping into too many windings or fewer windings with a core.

[nat1971a]

I thought i would post a very brief summary of the cited references from grays patent 4661747 that i glanced over the other day

3443142 - Patent regarding a spark gap in enclosure under pressure
3663855 - Patent regarding cold cathode vacuum discharge tube - carbon
3798461 - Patent regarding short pulse generator
3939379 - Patent regarding gas discharge tube - also ignition coil with primary made of copper sheet - four or five turns
4198590 - Spark gap with potential difference
4370597 - Thyratron

I would recommend that everyone has a glance through these references. It's very difficult to really take anything away from them other than a general idea of what they thought was relevant for the patent examiners. But 3-4 of 6 appear to be about the LV switching side of things.

Let me know if you want them posted

[mlurye]

Question to our gurus. Would it be a good idea to use this caps LOT OF 12 HIGH VOLTAGE 2400 UF 450 VDC CAPACITORS - eBay (item 330311029971 end time Mar-06-09 09:10:34 PST) as discharge caps? I'm thinking about putting 10 in a row (4.5kV).

[freeukpower]

Rtary Spark Gap

To Electrotek in your post 889 you reported having problems with the HV arcing across to the mains supply. This is a picture of the rotary switch I made some time ago **** Rotary spark gap on Flickr - Photo Sharing! ****. The motor is from a small desk fan and runs at 3000 RPM. The 2 sparking plugs are from the lawn mower. For the rotary contact centre electrode, I used a small section of SS tube with the centre electrode from a broken sparking plug brazed into each end. To get the spark gap to work the air gap has to be as small as possible.

I found that the speed of switching was not fast enough to get a decent HV discharge. As " lighty" in post 890 shows the RPM would have to be many order of magnitudes higher. Tesla experimented for many years to get higher speeds using DC motors, even going to having 2 motors contra rotating to get faster switching. Some authors attribute the development of the Tesla Turbine as a method of getting higher RPM into the 100,000's to reduce the time the contacts were close enough to arc across.

As a side issue I had great trouble with the arc dragging some 40 to 60 degrees away from the contact area. I found blowing hot air (80oC or hotter) at 3 to 5 PSI through the arc gap helped extinguish the arc quicker. I found better and more repeatable results using the reverse Diode arrangement. When I get chance I will post some more pictures of my recent experimentation and tabulated results of the voltages seen across the battery and capacitors on the LV side of the spark and from the collector grids of the CSET