Mr. Goodman asked yesterday:
> The tracking governor using a single ear sensor (Aeolian Themodist)
> seems to be under constant vacuum, i.e., it is active on the rewind.
> Does anyone have experience that will nullify my observation?
You are correct. The 3/16" supply tube for this system comes right
from the reservoir, and is under vacuum at all times.
This problem caused some discussion between Robbie and me; the result
is a paper I wrote for the MMD Technical archives, at:
On my Themodist, the single ear system works better than one would
expect during reroll. Apparently the finger cannot respond fast enough
then to jerk the paper around too much, so the centering pneumatic sort
of hovers about the midpoint. If the vacuum to the tracking system
were to be cut off during rewind, the roll would gradually move all the
way to the right. Then the paper, centered on the take-up spool during
play, might hit the left flange of the roll spool, and be torn.
On later Aeolian products, with two ears, and two opposed pneumatics
shifting the roll, the sensing lines from the ears, not the vacuum
supply itself, are cut off during reroll. Then both pneumatics are
under full vacuum, so they try to both close to the same extent. This
forces the roll towards the center of its range of motion, and holds it
steady there; a much better arrangement.