eBay Deal of the Day: Dalek Voice Modulator

I don't quite get what's going on here, but this appears to be some sort of early Vocoder that creates Dr. Who Dalek voices—or any other crazy noises—using old skool components. There are two inputs, one from a mic and one from an instrument, and one output. I suspect someone out there has some sort of electronics knowledge and can explain just what's going on there. Anyone?

GSS: 1 - Relatively Calm

Analogue Ring Modulator Synthesizer, Dalek Voice ? [eBay]

UPDATE - Tom sends us this.