Wallenstein had been the principal cellist of the New York Philharmonic and had then been the youngest member of the Los Angeles Philharmonic when it was founded in 1919 . Arturo Toscanini had encouraged him to become a conductor . The former principal cellist of the New York Philharmonic had been the youngest member of the Los Angeles Philharmonic when it was founded in 1919 , and had turned to conducting at the suggestion of Arturo Toscanini .