The Mellotron Mark VI is based on the M400 model ; it has the same features, but it also brings many improvements.
It now has a tube preamb, and not a transistor preamp anymore.
The wooden cabinet is stronger ; it has reinforced corners, and a thicker back. It is lighter than the original cabinets. Its finish can be polished mahogany, or it can have different colours (white, black, brown,...).
The capstan is made of stainless steel, and the belt's flywheel is slightly heavier, which makes the whole thing more stable.
The screws, bolts and discs are in metric standard. As the British standard (British Association) does not exist anymore, it is very hard to find parts using this standard when you're out of England.
The motor controller card has a switch aimed at "memorizing" two speeds. An indicator on the control board indicates the selected speed.
The motor is a new model, which is more stable.
The Mellotron Mark VI has a balanced 1/4 inch audio output.
A brand new tape frame has been created. It is lighter and stronger, and it allows to play longer tapes, which advances the time of playing by 20 %. This new tape frame also fit in the M400 and the Mark V.