MENDOMAID
My first zapper was the most simple - a 9 volt battery, 2 leads with alligator clips and 2 copper handholds. It seemed to work quite well for infections, cold sores and some other problems. It was time consuming to use but whenever the commercial zapper I'm using doesn't seem to be effective I go back to using the simple device.
I built a zapper from Clark's instructions and that worked well until it fell apart. Inexpensive commercial zappers, I've found are not always reliable, one came with a defective circut and several were not effective for some types of infections. Several of these lasted for only a short time before they corroded or the plastic parts failed. I usually buy zappers which use the basic design of Clark's son. I seem to have the best results with zappers which have broad frequencies.
Clark wrote that no current flows thru the body, the effect is more like the body is a capacitor which is charged, then the effect is cut off, then charged and so forth. This seems to stun organisms and they never recover. Imagine sound from a speaker which is turned on and off rapidly.