The Catalinbread Pareidolia Harmonic Mesmerizer is based around the 1961 Fender Twin Amp... The Vibrato in this amp was actually more than Tremolo. What exactly should the effect should be called? Vibrato? Tremolo? Modulated dual filter? Phasor? It's been called "vibrato" which isn't technically correct. It is an amazing sound though!! Truly the "sinewave" Brownface tremolo sound folks are looking for. Catalinbread used this as the starting point adding a lot more range of speeds and much more depth.
Catalinbread is convinced that once you turn on the Harmonic Mesmerizer, you'll have a tough time turning it off.