[emeritus]

Have you tried measuring the current drawn by the player in its various operation modes? The Philips EL3302 draws a pretty constant current of circa 100mA in play, record, fast forward and fast rewind modes, so a simple wire-wound series resistor of suitable wattage rating to drop the excess voltage was all that was needed to use it from a 12V car battery. They did sell a car kit consisting of a resistor in a ventilated metal box with some leads and a plug for which AFAIR they charged about a fiver in 1969: I made up my own.