The Hammond C-3 is a type of Hammond organ, produced by the Hammond Organ Company. The C-3 was identical sonically to the B-3, but with a different wooden casing. The C-3's casing surrounded the organ on all sides. Instead of these solid wooden sides, the famous B3 had legs supporting the organ, making it somewhat lighter and more portable.
In England, the C-3 was very common, and groups like Deep Purple, Fleetwood Mac, and Keith Emerson of ELP used it.
For most organ parts on Led Zeppelin's albums, John Paul Jones used the C-3 model, and it was a common instrument on many of their early tours. The C-3 can be heard on 'Thank You', 'Since I've Been Loving You', and 'Night Flight'. On the early Led Zeppelin tours, there was often a C-3 or B-3, but it was likely that these heavy instruments were made available for each show, rather than the group carrying one from city to city. (At the time, Hammond organs were very common, and many halls had one available.) The Hammond was a very common sight on Jones' right side of the stage from 1970 until 1975. The Hammond was always run through a Leslie speaker, which has become the traditional way to amplify a Hammond. The Leslie speaker contains an amplifier and 'spinning speaker' system that gives the sound animation and energy. Unfortunately, the Leslie amp was only 45 watts, certainly not enough to be heard clearly on the loud stages of Led Zeppelin. So, the band would put the Leslie offstage in the dressing room and place microphones near it to send sound to the mixer.