Re: how do these frequencies really work here?

Frqs can be delivered in more ways than just via DC electricity. Actually the more dehydrated your body is from modern Chemical warfare the worse the result of a contact device.

The zapper argument is that one frq with enough harmonics can cover nearly all pathogens. Now there is truth to that but as Hulda found out later nothing is every 100% effective. Even a lay person can tap a 9v battery and get benefit from it, a zapper especially those with more power like the Ultimate Zapper showed real results for me.

But by refining the frq and using a more powerful delivery system like an F165 one can go further. So to answer your question, there are programmable Frequency Generators like the F165 that can be used to drive a Plasma tube a Bean or used as a contact device.
http://www.electroherbalism.com/Bioelectronics/FrequenciesandAnecdotes/F100/