Wanna buy a Marantz CD-400B CD-4 disk demodulator ?
Cosmetically fair, and I checked that is works by injecting a carrier from a generator with a VCG function and modulated it. It was loosely coupled capacitively to the input, a wire near the jacks with the cover off. The signal came out of the outputs. I have a picture of that setup working.

Of course I have no CD-4 records, and no compatible cartridge, but I know it works.