Here is a WBUR (Boston) interview with Lehmann broadcast on 27 January 1967. The program was called: Hall of Song: The “Met,” 1883-1966. This was the 1933-1935 portion of the series. The Lehmann interview of this broadcast begins at around 5 minutes and lasts about 15 minutes. It is followed by a recording of Lehmann singing in Der Rosenkavalier.
