Part 3 of 4

With the preceding as background, it should be clear that, during the
reroll operation with an Ampico A or B roll on an Ampico B piano, the
'special' valve could be turned on and off (if only briefly) many times.
This would occur as the perforations on the roll in its 5B channel pass
over the 5B tracker bar port. This can, and does, generate a series of
variable-length bursts of faint, but often noticeable 'puffing' sounds.
The rewinding roll paper gradually speeds up across the tracker bar
during the reroll operation because paper continually 'accumulates' back
onto the supply spool. As a result, the perceived pitch of the puffing
noises increases. One could describe this noise as a chattering and/or
chirping sound.

The noise has two main sources. One significant component is caused by
the impact of the 'special' valve poppet (during the up-stroke) on the
upper valve seat when the valve is activated. Another component results
from the impact of the valve poppet (during the down-stroke) on the
lower valve seat when the valve is turned off.

Remember that the 'special' valve does not incorporate the ball bleed
device. A primary function of the ball bleed device (see pp. 34-35 of
the 1929 Service Manual) is to reduce the noise produced by the valve
poppet impacting the upper and lower valve seats. Consequently, the
absence of that ball bleed 'contributes' to the noise generated by the
'special' valve during the reroll operation.

It has been observed that the reroll chattering noise is evident
when the 'special' valve in the B drawer has a bullet-bleed with a #60
constriction opening. When the opening of the bullet-bleed is #70, the
chattering noise is substantially diminished.

The opening associated with the #70 (.028" dia.) bullet-bleed is
sufficiently small so that not enough time is available during the
'high-speed' reroll operation to exhaust enough air out from underneath
the leather pouch (of the special valve) to reset it. If the valve
is not reset, a subsequent 'turn on' signal is barely capable of
activating the valve. That is, the valve is still on and has not yet
been completely turned off. Therefore, little or no puffing noise is
generated. If a single puff is not generated, then the chattering
sound (consisting of a series of puffs) is not heard during the reroll
operation.

The opening associated with the #60 (.040" dia.) bullet-bleed is
sufficiently large so that enough time is available during the
high-speed reroll operation to exhaust air out from underneath the
leather pouch (of the special valve) to reset it. (The areal opening
of the #60 orifice is twice that of a #70.) If the valve is reset,
a subsequent 'turn on' signal is capable of activating the valve.
Therefore, a puffing noise can be produced. If a single puff can be
generated, then a chattering sound is heard during the reroll operation.

If your 'special' valve (C) has the offending #60 fixed-opening
bullet-bleed, there are several ways to correct the problem. The
simplest, but not necessarily the easiest (from the point of view of
manual dexterity) approach is to replace the #60 bullet-bleed with
one that has the #70 opening.

But first, this requires the nondestructive removal of the #60
bullet-bleed unit. And then one must have an available spare #70 unit,
with which to replace it. Extracting a bullet-bleed can be done with
a quality hand-held pin vise (e.g., Starrett, 162C) and a #42 (.0935"
dia.) wire gauge drill bit. This may be accomplished without damaging
any portion of the wooden valve block. The procedure for doing so
is best left for a separate article, hopefully to be published
subsequently. Be careful, the wall of bullet-bleed appears to be
tapered slightly. Be gentle, because the thickness of the brass wall
of the bullet-bleed is only about .005".

If extracting and replacing the bullet-bleed is too daunting, there are
other approaches that can be utilized to realize the same end result.
For example, one could insert (and/or glue) a 1/32"-thick piece of cork
gasket to cover the 3/32" diameter bullet-bleed insertion hole. Then,
arrange to have a #70 pinhole 'punched' in an appropriate place on the
'thin' cork insert. That way, the original #60 fixed-bleed can stay in
place, but the #70 cork pinhole serves to constrict the airflow to the
desired level.

Alternatively, one could insert a 'small' pre-drilled plastic or wooden
cylindrical plug into the opening of the 3/32" diameter bullet-bleed
insertion hole. Of course, one has to carefully drill a #70 hole in the
center of the plug ahead of time. As above, the original #60 fixed-bleed
can stay in place, because the #70 centrally drilled orifice serves to
constrict the airflow to the desired level.

Incidentally, if the fixed opening in the bullet-bleed is made too
small (i.e., > #70 wire gauge), the piano can shut off prematurely,
even before the piano roll has a chance to play. This can occur because
the shut-off pneumatic begins to collapse if the tapered leader of the
piano roll does not cover the 5B port at the start of play (a common
circumstance). The built-in 5-second time delay associated with the
shut-off pneumatic can expire (thereby completing shut-off) before the
'special' valve has a chance to be 'reset' by air being exhausted from
under its pouch.

The engineering circumstance described above is an example of the
Goldilocks principle: too large is not good, too small is not good, but
somewhere in between works! In this case, if the bullet-bleed hole in
the 'special' valve is too large, the puffing/chattering noise during
rewind becomes noticeable, if not excessive. If the bullet-bleed hole
is too small (and the 5B port happens to be open at start-up), the
piano will shut off before the roll even has a chance to play.

There is a bullet-bleed constriction diameter which allows the roll to
start up properly and which also prevents excessive chattering/puffing
noise from occurring during the reroll operation. That constriction
diameter appears to be at or near wire gauge drill size #70 (.028"
dia.).

A puzzling question remains. What explains the presence of a #60
bullet-bleed in the C valve in some original Ampico B pianos, while
others (also original) have the #70 bullet-bleed?

Bill Koenigsberg
Concord, Massachusetts

 [ To be continued ]

 [ Ref. https://www.mmdigest.com/Gallery/Tech/Ampico/amp34.htm 
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