Here's more information to save your rolls from tearing on rewind, but
it is most specific to the Dynavoice Keytop Pneumatic roll player, for
the two other people on the planet who will ever wish to rebuild one.

In the original configuration, the Dynavoice was known for its ability
to reduce an otherwise good roll to trash within seconds on rewind.  It
could happen anytime the roll was playing.  It could destroy a roll
before you could react and pull the plug.

The Dynavoice is "where the rubber meets the road" in the ongoing
discussion regarding absolute original restoration versus upgrades.
Very simply, if the Dynavoice system is not upgraded you will without
doubt, no matter how careful, destroy many rolls.

Having to constantly anticipate this happening, or actually having it
occur, will not make for an enjoyable experience when using this roll
player.  It will however, be just like the original experiences
suffered by original owners.   :o)

The fix (part 1):

The first part of the fix has other benefits, as it involves adding
a manual assist to the tracking system.  The back-to-back bellows that
control the side-to-side motion of the roll spool are located on the
right of the roll frame, and it is very easy to attach a push-pull
shaft to this little system.  The shaft is brought out through the
front of the case where a knob of appropriate size is added.  When
playing an other than perfect roll, you will find the manual assist
invaluable for keeping the roll tracking correctly.  More on how to
use it on rewind follows.

2nd part of fix:

The vacuum supply tubing to the automatic rewind bellows should be
disconnected from the bellows chamber and plugged.  This will keep
false rewind signals from occurring in the middle of a roll. Rewind
should only be triggered manually with the eject lever.

3rd part of fix:

A sewing machine variable speed foot pedal is introduced into the
rewind motor circuit.

When the end of the roll is reached, engaging the eject lever will
stop the forward motion of the roll and shut down the vacuum motor.
However, unlike the original configuration, the roll will not take off
into rewind at great speed and shred your roll, because the foot pedal
has the rewind circuit open.

To rewind, first carefully remove the roll from its chucks, pull the
left flange out 1/4", re-install in chucks.  (All loose left flanges
should have previously been removed and had a bit of tape applied to
the male fitting that goes into the roll core, to make it fit tight
enough to stay in position when pulled out from the core 1/4".  Of
course some flanges are pinned, but that can be dealt with as
necessary.)

Okay, now you have your roll ready to rewind.  Until you get
proficient at controlling the rewind, you can take it quite slow,
taking great care with the foot pedal, which is a little touchy at
first, until you get used to it.  As the paper wanders upon rewind,
you use the push-pull knob to keep the roll spool moving back and forth
whatever amount is needed to keep either paper edge from contacting
either flange the least amount possible.

When you get good at it, you can anticipate each time the paper changes
direction and begin the correction right away and rewind a roll quite
fast.  Don't try to do a fast rewind too soon, as it only takes one
mistake and you can have the paper climbing a flange.  If you do get in
trouble, you can immediately release the foot pedal and stop before any
extensive damage is done.

Before putting the roll away, be sure to gently tap the roll paper all
the way to the right flange, then push the left flange back into the
core until it just, ever so lightly, contacts the paper.

It just dawned on me that an original unaltered Dynavoice would make
for a great gag for "Candid Camera".  I can just imagine the reactions
and the expressions of the "victims" when they were instructed to play
a "very rare and expensive" roll for their boss, only to watch the
roll trigger the rewind about half way through, and disintegrate into
confetti, and festoons of paper ribbons, seemingly at the speed of
light.   :o)

Tom Lear
San Francisco, CA