Variable inductance tuning

The Philco 788 used permeability tuning on the band spread ranges too. All (or certainly most) car radios made from about mid 1950's also had permeability tuning. The tuning coil units were quite a lot smaller than a tuning capacitor/coil combination, so space savings were, most likely, one reason they became the mainstay in car radios. Another reason they were used was their temperature stability & resistance to shock. I don't know for sure if this was ever done, but it also would have been possible to wind the coils so the turns were closer together at one end of the coil compared to the other end. This would have enabled the radio to have been designed to have a more linear tuning range across the dial (preventing crowding at the HF end of the dial). Another possibility comes to mind too. It may have been much easier to maintain oscillator tracking with the aerial/RF tuning. With a tuning capacitor, perfect tracking (or more accurately, tuning) only occurs at two points of the dial - one at the low frequency end, and the other at the high frequency end

Maybe the La Wood tuners as well - as they were a prolific car radio manufacturer