It’s an early (prototype?) model of the first iteration of the memory man delay (distinguished by its unique enclosure) I worked on one in the hands of a collector a few years back (this is only the second or third I’ve seen) IIRC it’s very similar circuit wise to the production model solid state echo with boost switch apart from an OTA based voltage reference circuit that was later omitted

The schematic for that model without the OTA circuit dates it to January ’78 (same date as the 4 knob deluxe version and titled ‘economy memory man’) so this was likely from late ’77.