France issued this stamp in 1980 in honor of JS Bach. It is a painting by Jean-Picart le Doux. It is Scott 1691. The pipes are highly sylized and can't be linked to any particular instrument.
France issued this stamp in 1991. The organ pictured is that in the Saint-Nicolas Church in Wasquehal-Nord, in the very north of France. The stamp is Scott 2252. The organ underwent extensive work in 1985. This site has a bit of information on the church and the organ.
I have not been able to determine who the builder is, though the site says it is a German instrument.