 -- They have been sold to the public from 1946 to present, beginning in Germany with Jorgensen Electronics then gradually spreading worldwide by the 1960s.Kinds of tone generation have included tube or transistor analog oscillators & dividers, mechanoelectrical sources such as a few Hammond tonewheel combo models in 1969 & a Noble amplified reed combo organ in 1966, with fully digital beginning in 1974 and since becoming the predominant type.They have been made with one to three keyboards.