I just love it! In all sincerity, it is truly a delight and a privilege to be able to unabashedly wallow in this kind of Mellotron-obsessed geekdom with all of you folks. Some of the minutiae are things that it never would have occurred to me to even wonder about and it really makes me appreciate just how cutting-edge the instruments were as well as how hard the technology of the time had to be pushed to make them feasible.
This is a good point although a little intense! MKII capstans were ground to 3/10ths of a thou. along their entire length. Some achievement in 1964. The normal commercial tolerance for ground shafts is 1 thou. which would be audibly diabolical. We hunted high and low to find a supplier who could match and if needs be, improve on the original tolerance. Any more run out and you would hear it instantly. M300s can suffer with capstan judder as the extra long capstan is unsupported in the middle and this allows for deflection and ringing. They can be an utter bloody nightmare to dampen. You can find out more in Capstan Monthly, available weekly from any butchers.