Back in the late 1950's, hybrid auto radios with 12 volt plate tubes for all
except the audio output stages were built by Automatic Radio for Ford and
Chrysler. The first production was in 1958. A Motorola power transistor was
used in the audio output stage. A search through Sams Fotofacts for 1958 and
later should give you some schematics to start with. A trip to an auto
junkyard might give you a radio.