This is the high-value stamp (Scott 1710) in a set of four issued in 1976 by the former East Germany commemorating organs built by Gottfried Silbermann (1683-1753). This one located in the large city of Dresden in what is now Trnity Cathedral, formerly known as the Hofkirche. The organ was dismantled and stored during the war, and re-built in 1971, with restoration in 2002. This link will give you the specification of the organ and direct you to some pictures of the reconstruction. Other Silbermann organs in Dresden include the Frauenkirche which was destroyed in the war and then rebuilt and the Sophienkirche. Here is a fascinating discussion of the new organ for the rebuilt Frauenkirche.