The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com Military Quenched Spark Gap Tests 9" Pancake Coil:  500 Turns of 34 AWG wire This is working well on high power.  Discharge will exceed 12" if sufficiently insulated. A sidewards view showing the gap.  Note there is no light from the gap as they are enclosed in the washer sections. Frank sent this Quenched Gap that contains a combination of two companies disks - one that is silver plated copper disks which have been formed to the desired shape, and a second type that is tungsten soldered to brass machined disks. This gaps are based on the Lepel and Telefunken patents, the original Quenched Gap being patented by Kinraide in 1899 6 years earlier. The discs are made with a recess to accept an insulating washer.  Without the recess the arc occurs at the edges of the washer instead of the face of the disk.  Here I am using filtration paper.