Musser Ampli Celeste
This rare electro mechanical keyboard has an actual phase shifter stage for "VIBRATO" instead of the expected "tremolo-labelled-vibrato" like a Fender Rhodes.
The phase shifter is just a single BJT stage so the effect is subtle. It was so subtle I had to trace the preamp just to verify nothing was broken. When I realized it was a single stage phase shift, it made a lot more sense.
The variable resistor is courtesy of a Raytheon "Raysistor" which is yet another rare item!