Hi Jetijs,

I have dumped caps as the high voltage source and have also used the water sparkplug circuit...the last pic in the vid you see of the little coil of wire connected to the grid output, it pulses that coil. I used a different coil with a core of welding rod and had a magnet on it and the magnet jumped about 2-3 inches high, which was pretty surprising considering there wasn't much input.

It can also be recovered to a cap.

I just watched for effects and did not make any record or any detailed measurements of anything.

The GAP between both rods is SMALLER than the distance between the rods and the grids. So the choice path is across the gap, when diode shuts closed and the hv potential moves 90 degrees to grids, there is a further distance to jump. I believe this is important to incorporate this concept in any Gray Tube, otherwise the primary HV discharge could simply go to grids and not truly be using the LV side as the path to ground that it should take first. So make distance from rods to grids BIGGER than the rod gap distance.

I'll post some clips of vids I shot of some sparks in the tube. I did not get the magnet jumping on vid unfortunately, but it did as I mentioned.