Possible anachronism
When Tyrone and Maceo first discover Sonny's guitar, they don't understand where the sound will come from. Then Maceo figures out that it needs an amplifier and reaches into Sonny's duffel bag and pulls out an old tube amplifier. There was only a brief shot of the amplifier, but it did not appear to have a power cord permanently attached, as any electrical device in the '50s would have. Instead there appeared to be a power cord receptacle on the chassis like you might see on the back of a desktop computer, indicating the amp was built according to present day standards.
Did anyone else see this, or am I dreaming?