In late October 1965, Vox designer Dick Denney visited the Thomas Organ Company, who distributed Vox in the US, to advise on the design of a new line of US manufactured solid-state amplifiers. One of these amps was the 100-watt Vox Super Beatle, which featured a resonant boost.
In a company summary of their work with Denny, it was proposed that a top-panel selector switch could be used to toggle between “the normal maximum treble boost action and the selected resonant boost characteristic”. It was also observed that “an interesting wah-wah effect is obtained by operating the boost switch between its two positions. A remote control for this at the guitar would be novel, however, the cost and complication would probably be high.”
Thomas Organ Company engineer Brad Plunkett did some further design work, replacing the frequency selector switch with a potentiometer and using an Armstrong oscillator circuit that was suggested by his colleague Les Kushner. Plunkett tried it out with a guitar-playing friend called John
