Adding an AUX socket
In most cases, a line input (AUX) socket and switch can be added for a small additional cost. This will allow input from an MP3 player, bluetooth receiver or other device. The switch will select radio or AUX input. The sound quality when using the AUX input will be the same as the original radio (that is, not Hi-Fi).
Do not expect the sound quality of a vintage radio to be comparable to modern audio equipment. The larger (8 inch or bigger) speakers have a pleasant rounded tone, but even these do not match the frequency response of modern speakers.