The Tone Bender was being produced by Sola Sound in London, and sparked the UK's entry into the fuzz pedal market.Sola later made a Mark II version for Vox, and yet another version for Marshall called the Supa Fuzz.In America the guitar company Mosrite brought the Ed Sanner designed FUZZ-rite pedal to the market in 1966.
RE-BRANDING FUZZRITES, the GUILD FOXEY LADY and the ELECTRO-HARMONIX AXIS Circa 1967 Fuzz tone guitar was a hot commodity at this time, and the market for fuzz pedals was growing rapidly!
Those resources offered examples of audio amplifier circuits, diode clipping circuits, tone control circuits - practically everything found in modern fuzz/distortion/overdrive pedals.
Electronics engineers at the time often used these references, and many of those ideas were simply considered textbook examples of common electronics principles.
They are my categorizations, for identification purposes only.
THE BIG MUFF STORY BEGINS - MIKE MATTHEWS and JIMI HENDRIX The Big Muff tale starts in the early 1960s with Mike Matthews, a college student studying electrical engineering at Cornell University in New York.