Re: Little Marx gen
Dr. Shark, Wed Mar 28 2007, 05:31PM

nice setup, but I can almost smell the corona that you get from all those exposed sharp edged Did you only run it at 10kV so far or did you try pushing it to the limit of the 30kV caps?

Re: Little Marx gen
vasil, Wed Mar 28 2007, 08:50PM

I didnt push it yet at the maximum voltage (short resistors and some breakdown along them). I am waiting some new longer res. Yes, there are sharp edges, i can insulate them with plasticine. I have to tinker a bit.
What would be the maximum spark for this setup? 20 cm sparks? I think it is the safer level.

Re: Little Marx gen
vasil, Fri Apr 13 2007, 01:22PM

My longer resistors didnt come yet, but I gave it a new push with some sligthly longer 9M1 resistors, covering the sharp edges and with higher input (still 60% of maximum, more voltage = breakdown along resistors). 13-14 cm sparks, pics on the page.

pic

movie

Re: Little Marx gen
vasil, Mon Apr 16 2007, 09:34AM

If I would use inductors instead resistors, how much inductance would be necessary per stage (minimum) to be in the ballpark? The coils can be air cored? I remember Steve Ward demonstrated such a setup at the thon. Some tips please?

Re: Little Marx gen
Steve Ward, Mon Apr 16 2007, 09:14PM

Inductors:

the inductors used on our marx generator were actually small ignition coils (well, not quite, they were really "magnetos") without a primary winding, and with the iron cores pressed out. They measured 4 HENRIES on my LCR meter, and only a few K ohms (assuming my meter worked properly with the high inductance). The higher inductance forms a lower oscillatory frequency for the output discharge, which allows for more jitter in the system before performance degrades significantly.

I later attemped to replace these magneto coils with my own home wound inductors. With a 2.5" PVC pipe and about 4" of 36awg winding, i did get some results (only a 3 stage marx was built). But, the output was not as long as when using the magneto coils, or resistors. So the inductance wasnt enough with this set up, so i decided it just would not be worth the effort to wind my own inductors in this manner. Perhaps adding a ferrite core (encapsulated in epoxy for insulation) to the inductors would help by increasing the inductance by a few times over, but the amount of ferrite needed would get to be more expensive than the price of the magneto coils, so once again i dumped the idea.

Re: Little Marx gen
Dr. Drone, Mon Apr 16 2007, 09:34PM

Re: Little Marx gen
teravolt, Tue Apr 17 2007, 03:28AM

I used two 2 watt 750k resistors I found them on ebay. This is one of two units that eventuly will put out about 1.5MV when added to gether. My picture is a video capture, can any body tell me what they do to catch a digital picture of the spark

Re: Little Marx gen
Steve Ward, Tue Apr 17 2007, 03:36AM

My picture is a video capture, can any body tell me what they do to catch a digital picture of the spark

Since my marx fired with a relatively consistent period, i was able to capture pics using my camera with a 1 second exposure time, though even still it was "hit and miss".

Re: Little Marx gen
Dr. Drone, Tue Apr 17 2007, 04:37AM

Re: Little Marx gen
vasil, Sat Apr 28 2007, 06:49PM

"THIRD STEP
Longer resistors.......maibe they will come finally.....
..................................... ..........................
....and they came, but what desillusion...They are longer but with terminal metal caps, so they were shorted almost imediately along the surface. Desperately I used some low power 510 kohms resistors (2 in serie for 1 Mohm/ stage). The spark rate was higher and the sparks longer (the caps charge at higher voltage), but the base ones smoked in a few seconds. Here is what I used:

s..ty resistors

I put again my trustfull 9M1 resistors and open the gaps a little more. I got 15-15,5 cm sparks, but soon the first two resistors (at the base) arced over. So the little game is over until I will get some good resistors....a project never ends isnt it? :)

movie