Hi; When I talked about my troubles with single finger trackers the
other day I should have described how I got the last one I struggled
with to work. I think this was an old Hardman-Peck player (this must
have been 20+ years ago).
This was a single finger system with a spring trying to pull the feed
spool over to the right and a pneumatic trying to pull it to the left.
The pneumatic would collapse until the left edge of the roll hit the
tracker finger, that would dump vacuum from the pneumatic and it would
constantly seek a balance point.
It would work very well during play -- in fact, it held the roll
dead-on as there was no margin for error before it would try and
compensate. The problem would arise when I went to rewind, and the
tracker (still being active) would try and move the feed spool (the
wrong way now) as the roll rewound.
This thing had a spring-loaded flange on the take-up spool to keep
the paper from telescoping during play and, if things were perfect,
it could rewind okay but the second it started to "hunt" during rewind
-- disaster! I tried slowing it down with a bleed in the vacuum feed
line, but that really didn't cure the problem.
The solution took a bit of work. I made a large pneumatic that would
get vacuum only during rewind. This "centering" pneumatic would push
the movable board of the tracker pneumatic shut until it came up
against an adjustable stop inside the centering pneumatic. I recon-
nected the tracker pneumatic to receive suction from the stack so
it would be inoperative during rewind. By adjusting the stop in the
centering pneumatic to hold the roll at the mid-point of tracking
everything worked fine.
I must be missing something on these as they had to work okay
originally but the few I have had experience with have all had this
problem. If anyone else has insight on this I'd love to hear about it.