An organ that produces sound using electronic circuits, as opposed to a traditional pipe organ which produces sound using pneumatics. Electric organs were the first popular electronic instruments, beginning in the 1930s when Hammond marketed their Model A. The market for electric organs grew rapidly after World War II, and brought about a number of manufacturers including Hammond, Lowrey, Baldwin, Thomas, Kimball, Allen, and Wurlitzer (the latter two being pipe organ manufacturers who went into electronics) in the USA; Jennings and Microvox in the UK, Viscount in Italy, Eminent in The Netherlands, and Yamaha in Japan. Generally, they were fully polyphonic, having a set of voice circuitry for each key in the keyboard's span. There were usually built into consoles resembling the consoles of pipe organs, and using the same types of controls such as "tab" switches to control timbre selections. Many models had dual manuals, and a few top-end models came equipped with three manuals. Some also had "pistons" or other mechanisms for selecting combinations of stops -- a form of patch memory.
With the notable exception of Hammond, which used the tone wheel system, most of these were fully electronic. Baldwin organs used neon lamp oscillators, several in combination for each note, in order to produce the various timbres. Most other brands used a form of divide-down or top octave division.
In the 1960s, the combo organ became a widely used instrument in popular music. Most combo organs were limited timbrally compared to larger console organs, but they were far smaller and lighter, dispensing with the console wookwork for lightweight molded plastic cases. They were easier to transport, and less expensive, these being particularly important attributes for rock bands in the mid-1960s. Many combo organs were made and sold under brand names associated with electric guitars and guitar amps, such as Fender, Gibson, and Vox.
In the 1970s, electric organs added "play-along" features such as built-in (usually rather simple) drum machines, and the ability to play backing tracks from a built-in cassette tape player. "Auto chord" systems, in which the performer could press a single key and then a button corresponding to a desired chord, with the organ filling in the notes of the selected chord in the proper key, became popular. Some organ manufacturers started to add synths to their organs; a notable example was the Thomas company, which built a Moog Satellite synth into several of their models. (Some sources claim that far more Satellites were built into Thomas organs than were sold as stand-alone instruments.)
In the 1980s, synths took over much of the territory covered by electric organs, and as a result few were manufactured after about 1985. However, some older models, notably the tonewheel Hamonds, are still prized for their timbres and sound qualities by the performers who play them. Since 1990, a number of sample playback synths have been introduced which specialize in reproducing the sounds of certain classic electric organ models.