Radio output volts AC DC

1973 Dodge Monaco factory radio question.
Input voltage is 12.6V direct voltage
Output voltage at left rear speaker is 31V to 0V alternating voltage. There is no direct voltage at speaker or fader.
Does the radio have a transformer internally that converts DC input to AC output?
I am a stereo neophyte so all help in understanding is appreciated.
Author: 1970FuryConv