Here's a nice clip from a 1984 episode of Late Night with David Letterman.
Jack Paar is the guest. He hosted the Tonight Show before Johnny Carson (from 1957-1962) - in New York, from the same NBC studios where Dave was then doing Late Night.
At the end of the segment, Paar surprises Letterman with a hidden artifact - still preserved in the building - from his Tonight Show days. It's quite remarkable.