2.8. Assembling the Corona Shield
When attaching metal pipe to fittings, apply a thin layer of glue to one side of the pipe only. The other side should remain bare to provide electrical contact. A thin layer of glue may be applied to the outside once the fitting is in place. Soldering the fittings is neither necessary nor desirable.
There are two small brush holes and two large collector holes in the corona shield. Remove the protective paper from both sides of the shield and place it on the leg sockets, with the collector holes at the lower right and upper left corners of the figure (seen from above). Arrange the metal pipe and fittings as shown. Collector (t) goes directly over the brush hole. A tee (s) passes through the hole in the shield. The collector is connected to the inductor (w) via two 45 degree elbows (u) and a length of pipe (v). The end of the inductor is sealed against corona loss by an endcap. Study the figure carefully. It is imperative that (t) lies directly over the brush hole in the corona shield and (w) lies directly over the neutral brush. Both (t) and (w) should line up with the rods as they pass beneath. Only after you are confident that the shield, pipes, and fittings have been arranged correctly, glue the pipe to the fittings, the fittings to the shield, and the shield to the leg sockets. Do not glue the leg sockets to the legs as you will need to be able to remove the shield if the belt ever needs replacing.
After the glue has set, remove the shield and flip it over. Pass a brush (g) through each of the brush holes as shown.
Tape each brush to a collector. I have used transparent tape so the brush can be seen, but you may use electrical tape. Replace the corona shield and adjust the leg sockets to ensure that the collector brushes make contact with each rod as the disk is turned. If the brushes are too short or too long, you may remove the tape and reposition them.
The rods should now make electrical contact with the collector via their brushes. Each rod should make electrical contact, via the neutral brushes, with the rod on the opposite side of the disk as it passes beneath the inductors. If this is the case, gently turn the pulley clockwise and make sure that this disk runs true, parallel to the neutral support and corona shield, and that the rods contact all four brushes. If everything is as it should be, you will be able to draw a spark if you place your hand between the opposite collectors.
Assemble the lower collectors and spark gap as shown. Note that only one of these assemblies, the spark gap, has an endcap at each end. When you understand the figure, you may glue the pieces together, allowing for electrical contact, as before.
Add the lower collector to the underside of the collector tee (s). Adjust it so that it is parallel to the upper collector and does not interfere with the rotation of the disk. This figure shows how the collector brush passes through the corona shield to make contact with the rods. When you understand how the lower collector should be positioned, glue it in place, allowing for electrical contact with the tee.
A 1 inch length of pipe (z) goes in the upper end of the tee. Do not glue it in place. You will need to remove it if you want to add accessories.
This completes the construction of the Dirod. The spark gap can be placed, not glued, on the corona shield as shown. When the pulley is turned clockwise, you should easily be able to draw an inch of spark. This corresponds to a potential of approximately 60 kV. If you fail to get anything, use a hair dryer to thoroughly dry the disk and corona shield and then try again. If you still get nothing, email me a couple of pictures of your Dirod and I will see whether I can spot the problem. Pay particular attention to your brushes.
The current, but not the voltage, is increased with increasing rotational speed. There is no need to go crazy with the pulley, however. At high rotational speeds, the upper bearing starts to wobble and the rods may fly off. This kind of speed is counterproductive anyway, because the brushes don't have time to rebound before the next rod comes around. Take it easy! A comfortable, controlled speed is all that is required. If the upper bearing is noisy, you can add a single drop of light machine oil, but take care that the oil doesn't drip down the main axle onto the belt.
In the likelihood that your Dirod is producing sparks, take it into a pitch-black room and let your eyes adjust to the dark. Start running your Dirod without the spark gap in place. You will see the corona we have been speaking of as a faint purple glow interrupted by sparks. Anywhere you see such a glow, corona is leaking. If it is leaking from a sharp point, you can file it down and/or coat the point with epoxy. If, on the other hand, corona is crossing the disk from one collector to the other, you are producing the maximum potential possible with this size Dirod. Higher potentials will only be possible with a larger disk.