Hi Ian

Franz Lamberts main instrument used in the later part of the 70s and early 80s was the Galaxy organ as seen in the video, so it’s most likely the one used on the cassette you have, there are also odd ones where he features the smaller Helios, however the Helios was primarily bought to the fore by Klaus Wunderlich. (Both were of the analogue era and were produced (With many updates) between 1977 & 1983/4)

Hope the above information helps

Bill