I came across this copy of America's Top 40 Countdown show done by Casey Kasem on 7/7/79. It featured the top disco hits of the previous 5 years. If you like electronic dance music, especially if you are into remixes, you can go through this whole show without hearing at least 10 bits of music that have been sampled for current tracks. If you have got some time to kill it is a great listen and despite Casey's cheeze factor he was masterful at delivering top 40 music to the country.
Here is the file, I think it will be a right click, save as.