Triggered Spark Gap

My trigger gap is a variation on the version in common use by many coilers. The main gap consists of two electrodes mounted in PVC pieces (the horizontal part of the "T"). The trigger electrode is also mounted in PVC (the vertical piece on the top). The trigger is fed by a standard ignition coil that is fired by a modified fan control. The circuit board mounted to the top PVC piece contains a series-parallel configuration of caps I had on hand and serves as a blocking cap for the ignition coil. The trigger electrode is connected to each main electrode by 70M of resistance to keep it centered. On the bottom of the entire assembly is mounted a vacuum fan that pulls air in through each of the electrode PVC pieces. It is a surplus vacuum from a bank tube transport system. This thing really moves the air and should be able to quench well for even bigger coils.

Here is a closer look at one type of main electrode that I have used. Each electrode consists of a .5" brass rod mounted inside the PVC piece with threaded rod. The threaded rod can be adjusted to center the electrode.  The electrode tip is mounted to a .125" piece of tungsten carbide drill blank with a set screw. That .125" piece then fits into a matching hole drilled into the end of the brass rod. A set screw in the brass rod allows the tip to be extended about .75" for gap adjustment. These carbide tips came from Marc Metlicka. One nice feature of this assembly is that the pieces are easy to swap in and out when I want to adjust them or try different electrodes.

Here is a good look at the other type of electrode I have used---a .25" tungsten carbide drill blank mounted into the end of the brass rod with a set screw. This one shows the effects of about 2 hours run time. It cleaned up easily with a bit of fine grit sandpaper. In the photo (at about 10:00), you can see a hole drilled in the PVC that allows access to the set screw. That allows me to adjust the gap without removing these PVC pieces.

Here are two varieties of trigger electrodes that I have tried. They both mount to a .5" brass rod, centered in the top piece of PVC. They are positioned so that the main electrodes fire through the center of the ring (or partial ring).