Although I don't have exact dates (sometime in early to mid seventies), the story goes like this.
During the sixties and early seventies, Superscope was the primary (if not the exclusive) USA distributor for Sony products. Then, Sony set up their own elaborate marketing enterprise in the USA -- and cut Superscope out of the action.
This hit Superscope hard. To survive, they purchased Marantz. Around that same time, the Superscope line appeared. A look inside quickly revealed that the Marantz products and Superscope items were produced at the same factory.
Later, Superscope sold Marantz. I don't recall if they sold it directly to Philips or if Superscope sold to an intermediate investment company and they sold to Philips, but either way by 1980 or so Marantz was a Philips subsidiary.
Superscope retained the right to make those little high-quality portable cassette recorders and market them under the Marantz name. To this day, parts for those machines are purchased from Superscope Techologies, which is itself a division of some other company.
Fred Longworth