This little gems are from a small group in the files of the then Harman Kardon Industrial Designers. They are of course highly detailed and very likely one of a kind.
You get a blueprint along with internal correspondence and other design drawing in their original Shin-Shirasuna Electric Corp. folders (2 folders). At a later point Shin-Shirasuna apparently bought much of Harman Kardon’s audio division in 1979 and had already been providing the design work for the company.
Also included is the HK 330 brochure and owner’s manual.