Before television took over the airwaves, Rockefeller Center was home to the National Broadcasting Company during the golden age of radio. This promotional film from around 1948 chronicles the rise of the media company from a small collection of 20 affiliated stations, formed in 1926, to more than 170 stations two decades later. The 24-minute documentary, courtesy of the Prelinger Archive, introduces the network and goes behind the scenes at Rockefeller Center, peeking into the mail room, sound recording studios, and music library.

The documentary closes with a look at the network’s budding television enterprise. “Adding sight to sound, [NBC] opened an electronic window” when it launched the first commercial television station in 1941, the narrator explains. “More than two decades of NBC radio have been dedicated to the spirit of public service. Now, in bringing television, network television, out of the laboratory and into your living room, NBC rededicates itself in this same spirit to provide the greatest medium of mass information and mass entertainment in the world.” Radio junkies and30 Rock fans alike will enjoy this journey back in time.