Simplify the following text for a Grade 11 native English-speaking person.
Original: He was Chief Conductor of the Netherlands Radio Orchestra until 1983 . While Downes worked with many of the world 's symphony orchestras , he enjoyed a particularly long relationship with the BBC Philharmonic ( formerly the BBC Northern Symphony Orchestra ) , serving as its Chief Guest Conductor , then Principal Conductor , and finally as Conductor Emeritus .
Simplified: He was Chief Conductor of the Netherlands Radio Orchestra and the BBC Philharmonic .