ahh busted! the master has spoken, after coming back from holiday. so here it is, by adjusting the trimpot, i can get somewhere 600KHz - 1.6MHz oscillation. most opamp/comparator circuit i've seen need at least one capacitor to work as oscillator, but this one no need. configure as "theorized" voltage follower, and just one trimpot to make it adjustable, the other 10K ohm is a standard issue, every LM393 need one to work.