Re: Old car radio - how to change polarity?
As others have said, it depends on the model. My Philips 493VT hybrid from 1961 has a polarity panel and the service sheet gives instructions as to what links to change on that panel to go from positive earth (as supplied) to negative earth to suit more modern cars. If no panel is fitted, then a DC to DC converter may be the way forward. It is possible to completely isolate the radio and its aerial but when I did it some years ago I found it a bit of a fag insulating the radio, its mounting screws and coax outer.
Ian
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