Don't Touch That Dial
Here's a tumblr worth visiting more than once: Old fashioned and beautiful. The range of different types of sound quality is charming. You can make quite a sound-clash by strategically using the play/pause buttons on several clips at a time.
Of their content they say:
"All programs are considered to be in Public Domain unless noted otherwise."
Their 'Random Program' button can lead in interesting directions.
"...is a simple tumblr that collects radio shows and advertisements now in the public domain. The archive is pretty great..."
Free image from the noun project.