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MMD > Archives > October 2001 > 2001.10.30 > 08Prev  Next

Ampico B Rewind Problems
By Craig Brougher

D.L. Bullock was asking:

> When the transmission goes into rewind, it begins winding and the
> shifter then slips a tiny amount out of rewind.  This stops the roll
> action and begins a tick, tick, tick as the tips of the pins hit
> without locking in enough to pull the roll.  I have strengthened the
> compass spring but to no avail.

The transmission employs an "over center" compass spring to keep the
transmission in reroll position.  It cannot "slip" out.  But what is
happening is probably the replay pneumatic is bumping the transmission
back into play again, and not quite getting it all the way back to
play.  Just little "bumps."  This could be caused by a leak in the
pallet #2 line.  Suspect the repeat switch, especially if it is old.
Watch "D" valve.  If you see it flutter, then you know.  The other thing
I can think of is that it's mistubed (my main suspicion, considering
the other problem).

Also, the two brake control collars on the transmission should not
touch the flat spring when in play or rewind.  Only when repeating.
The pony brake only stops the transmission momentarily to allow it
to switch back into play quickly from reroll.

> I also have a problem playing A rolls because of the #5 Bass hole
> that was crescendo for A rolls is the Replay pneumatic for B rolls
> and the drawer.  This is especially bad if the transmission had
> trouble staying in rewind anyway as the fast opening of that hole
> gives the system a quick kick out of gear.  Is there a better place
> to put this tube?  Perhaps to the unused sub-intensity as these are
> both A expression pianos?

5B only "arms" the repeat valve.  It doesn't actually make a roll
repeat, and it doesn't operate the pneumatic.  For that, you need the
pallet valve #2.  I strongly suspect that your repeat circuit is either
mistubed, or that you have a fluttering valve, caused by an old,
unreplaced (sticking) ball bleed in the "D" valve.

It's obvious that 5B doesn't operate the repeat pneumatic, otherwise,
every time a fast crescendo went by, you'd hear this click and the roll
would stop turning.

Don't use any old ball bleeds.  You cannot clean them.  You cannot
resurrect them.  We have cut them in half and checked the effectiveness
of sonic cleaners, etc.  It's a worthless idea.  Don't do it.  Robert
Streicher makes new ball bleeds.  You will always get a few sticky
ones, but not many, and they are cartridge-tight.  Use them.

> One other question to those of you who have done numerous B drawers:
> On the four-valve block "rewind/replay/brakes/shutoff" box, one piano
> had the following and one did not.  Which works better?
> On the lower right valve block there is a cardboard insert into the
> top metal valve seat that has a small hole drilled into it.
> Obviously it is to slow down the off portion of its activity.  Since
> both of these drawers worked before the restoration, should this
> cardboard disk be replaced or not?  Was it factory or previous
> rebuilders that put it in?

The lower valve is called "C" valve, and the cardboard with the pin
hole was put on it to increase it's actuation speed and slow its return
speed, just in case the roll's leader and the drop of the pallet #2
occurs simultaneously.  I'd go with the cardboard-pin hole idea.

Craig Brougher

(Message sent Tue 30 Oct 2001, 15:13:58 GMT, from time zone GMT-0800.)

Key Words in Subject:  Ampico, B, Problems, Rewind

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