Vintage DataBooks are a valuable source of Electronic Product Design Ideas. Study the Applications.

Folkscanomy Electronics: Books on Electronics, Circuits and Processors 

You will also find Radio Electronics and many other Datasheets. Even of firms that do not exist now.

One of the books here is The ” Intersil Hot Ideas” – This was my Mentor Book These helped me build Intelligent Instruments in the 80s. Intersil  was in advanced CMOS before anybody else. They made the smartest chips when the Microprocessors were being examined Skeptically by engineers. (At that time Microprocessors needed many support chips and consumed huge power only later CMOS uC came)