The Mark I is the very first Mellotron model, based on the same concept as the Chamberlin 600 Music Master (see A Mellotron history).
Because of their reliability problems, most Mark I's were converted to Mark II's when this model was released in 1964.
Except for some technical details, Mark I and Mark II are quite similar.
The finish of the Mark II cabinet was polished mahogany. Only five Mark II were black with a gold serigraphy (Pink Floyd and John Lennon had one of these).
Mark II had two 35 note keyboards (G to F). The left hand keyboard is divided in two parts : a rhythm section (keys 1 to 17) and an accompaniment section (keys 18 to 35). The right hand keyboard played the lead parts among 18 instrument sounds.
Mark II used 3/8" tapes. The sounds were recorded on 3 tracks, one sound on each track.
Each keyboard used 6 banks of 3 sounds. One selector granted access to one of the six banks, and another selector allowed the player to chose one the 3 tracks (A, B, C) in each bank. For the accompaniments and the lead instruments, the selector had black buttons, which were aimed at playing two tracks together (A+B or B+C).
The tapes were fixed on a drum at the front and the rear. During the change of sound bank, a warning light flickered, and a locking system prevented any action on the keyboard. The drums were activated by a motor using a chain. A special tape was aimed at locating the different banks. Once the tapes located the desired bank, the warning light stopped to flicker, which meant that the Mellotron could be used.
Many bands (Genesis, The Moody Blues, King Crimson...) replaced the rhythm and accompaniment sounds of the left keyboard by the right hand keyboard's sounds of lead instruments. The most famous example of the use of a double lead instruments keyboard is the intro of Genesis' Watcher of the skies : left hand keyboard = accordion ; right hand keyboard = violins + brass.
Mark II had two 12" built-in speakers, a tube preamp, two transistor power amps and a spring reverb. The replay heads had a high impedance. The internal circuits used alternating current. The motors' speed was controlled by a V.F.O. (Variable Frequency Oscillator). The VFO delivered 150 volts, and its frequency was variable (10 to 100 Hz). This system was very fragile ; as a consequence, from the FX Console, the next Mellotron models used direct current, and their motor was ruled by the CMC4 control card.
Compared to the sound of other Mellotrons (and most notably the M400), the sound of the Mark II is quite typical. Because of the use of a tube preamp, its sound is warmer, sweeter, softer. It can be found on King Crimson's first three albums (In the Court of the Crimson King, In the Wake of Poseidon, Lizard), Genesis' first three albums (Trespass, Nursery Cryme, Foxtrot) and the first Moody Blues records.
Ron L. Hubbard reportedly had a Mark II too. This Mellotron was ordered in 1965, was played until 1967, but has not been used ever since. It is one of the best preserved Mark II today. After a small repair at Streetly Electronics, it has returned to the Scientologist Church.
Princess Margaret and Peter Sellers are a few of the other personages who have owned a Mark II.