Concentration is an American television game show based on the children's memory game of the same name. Matching cards represented prizes that contestants could win. As matching pairs of cards were gradually removed from the board, it would slowly reveal elements of a rebus puzzle that contestants had to solve to win a match. The show was broadcast on and off from 1958 to 1991, presented by various hosts, and has been made in several different versions. The original network daytime series, Concentration, appeared on NBC for 14 years, 7 months, and 3,770 telecasts, the longest run of any game show on that network. This series was hosted by Hugh Downs and later by Bob Clayton, but for a six-month period in 1969, Ed McMahon hosted the series. The series began at 11:30 AM Eastern, then moved to 11:00 and finally to 10:30. Nearly all episodes of the NBC daytime version were produced at 30 Rockefeller Plaza, New York City. A weekly nighttime version appeared in two separate broadcast runs: