Auto radio's like my Transitone had "B" battery's only,before 1932, I also have a Transitone 3 from 1931, The RCA M32, that I have, has a motor generator for B voltage ,but it could have used battery's also, The 1932 Ford radio built by Magestic also used a motor-generator, Late 1932 Mallory came out with a vibrator power supply B eliminator. Now if you see old movies with air planes from the early 1930's you may notice a small porpeller under the wing ,this is the generator for the B voltage for the planes radio!
