Simplify the following text for a Grade 9 native English-speaking person.
Original: In 1937 , Karajan first conducted the Berlin Philharmonic and the Berlin State Opera He was very successful when he conducted Tristan und Isolde .
Simplified: In 1937 Karajan made his debut with the Berlin Philharmonic and the Berlin State Opera , conducting Fidelio . He then enjoyed a major success at the State Opera with Tristan und Isolde .