Educational Television and Radio Center

1952-1957

1957-1966

1966-1970

1970-1972

Public Broadcasting Service

1969-1970

1970-1980

1980-1985

1985-1988

1988-1992

1992-1995

1994?

1995-1999

1999-2000

2000-2006

2005-2012

2012-2019

2019-Present