MJC wrote:



Sure, but my point was that any chatter in the bearings is just as bad
as rotational variation and is not damped by the flywheel. So the plain
bearings have to be accurate and long-lasting.


** You have completely forgotten the damping effect of side-ways
pressure from the pinch roller.


I certainly was not taking it into account. Probably because it is
movement along the length of the tape and not sideways that gives rise
to speed modulation at the pick-up.


** Just to rub it in, the SIDEWAYS pressure from the pinch roller forces the capstan shaft against the bearing and inhibits any "chattering".

I really works and I see machines ( ie Roland Space Echos) with noticeable play in the capstan bearing that have low W&F.


..... Phil