Anton Walter

[1] In that year he was joined in the firm by his stepson Joseph Schöffstoss, and the pianos came to be labeled "Anton Walter und Sohn" ("and son").

Like all early pianos, those of the Viennese school were of far lighter construction than modern instruments and had a quite distinct sound; for general discussion, see fortepiano.

Walter improved on Stein's design by adding to the action a back check, which caught the hammer on its descent, preventing it from bouncing up and down in lively playing.

[1] This innovation was generally adopted by other Viennese makers in Walter's time, and remains standard in the modern piano.

Contemporary and earlier instruments by Johann Andreas Stein, liked and played by Mozart, do have the knee levers for the dampers.

For more on Walter and his pianos, see the relevant chapter in: Michael Latcham, Pianos for Haydn, Mozart and Beethoven: change and contrast, published by Katzbichler, Munich and Salzburg, 2017 In modern times, fortepianos have been constructed by a number of builders for purposes of historically informed performance of 18th century and early 19th century music.

Anton Walter. Oil painting by Friedrich Gauermann , 1825 (Vienna, Kunsthistorisches Museum )
Fortepiano by Anton Walter & Sohn (Vienna, ca. 1805) – Berlin, Musikinstrumentenmuseum
Mozart's Walter, on display in the main hall of the Tanzmeisterhaus , where the Mozart family lived in Salzburg after 1773. The location (now a Mozart museum) is ahistorical; during his lifetime Mozart kept the instrument in his adopted city of Vienna.
Fortepiano by Paul McNulty, based on a historical instrument by Walter & Sohn, 1805