Part 2 of 4

Interestingly, there is one valve in the Ampico B drawer that has the
usual bullet-bleed, but its fixed constriction opening can differ in
diameter from one Ampico B piano to the next. In the diagram on page
50 of the 1929 Ampico Service Manual, this valve is labeled C (located
at lower right position). It is one of four valve block bodies (one is
a blank) mounted on a drawer assembly that is denoted as 'Control Valve
Block' in the left side of the Ampico B drawer.

https://www.mmdigest.com/Attachments/23/02/02/230202_162836_Control_Valve_Block.png

This 'C' valve sometimes has the word 'special' typed on a small piece
of paper that was originally glued to its rear surface (the one with the
5/32" diameter elbow). The 'special' paper notation (not always present)
refers to two distinguishing characteristics. The first is that the
ball-bleed device in this valve is absent, with related internal
passageways blocked off, of course. Refer to the next paragraph for a
more detailed explanation regarding how the passageway is blocked off.
The second characteristic is that the metal-top valve cover incorporates
a thin exterior cardboard insert with one or more pin-prick openings.

In the wooden B valve body, there is a passageway (3/32" diameter) that
goes from the gasket face of the valve block to the underside of the
leather activation pouch. This pathway would otherwise serve as the
channel through which air could travel to the ball-bleed device, if it
were present. However, in the special valve, this path is blocked off
with a separate bullet-bleed cup whose bottom surface does not have any
drilled opening at all.

On some Ampico B pianos, the normal bullet-bleed in the 'special' valve
exhibits a #60 opening. This contrasts with other Ampico B instruments
which have a #70 opening for the bullet-bleed in the 'special' valve.
As of this writing, it appears as if some early (1929-1931?) Ampico B
pianos have the #60 opening in the bullet-bleed cup, whereas some later
Ampico B pianos (1935-1937?) have the #70 opening.

It is possible that some Ampico B drawers will subsequently be
identified that have 'special' valves with a bullet-bleed fixed opening
that falls in between wire gauge #70 (.028" dia.) and wire gauge #60
(.040" dia.). This dimensional observation is based on 'go no-go'
measurements made with precision drill bit shanks (or just visual
inspection) for only a limited number of Ampico B instruments (about
15 or so).

It is not at all clear that there is a pattern associated with the year
of manufacture of the Ampico B drawer and the presence of a specific
diameter of constriction in the corresponding bullet-bleed cup in the
'special' valve. However, it is reasonably clear that Ampico B pianos
with the #60 opening in its bullet-bleed ('special' valve only) behave
differently during the instrument's reroll operation than those with the
#70 opening. The difference is described below.

The purpose of the fixed bleed cup in the 'special' valve (and others,
as well) is to provide a path through which air can be exhausted from
the space beneath a flexible leather pouch after the valve has been
activated and then turned off. This exhaust process quickly 'resets'
the valve in preparation for its next on-off operation. However, the
intended function of this one 'special' Ampico B valve is to be
activated just once. That operation takes place after the piano roll
has been played and the subsequent rerolling process is at the point
where the tapered 'leader' of the roll is about to disengage from the
take-up spool.

The port in the Ampico B tracker bar that activates (turns on) the
'special' valve is port 5B. On an Ampico A piano, that port corresponds
to the fast bass crescendo function. However, during the reroll
operation of the Ampico B mechanism, vacuum is still being supplied to
the 'special' valve. Consequently, pneumatic signals can be sent to,
received by, and acted upon by the 'special' valve during the reroll
of an Ampico A or B roll on an Ampico B piano.

By design, the bass and treble crescendo operations on an Ampico B
piano are activated concurrently. That is, the 1T port simultaneously
activates the slow crescendo for both the treble and bass sides of the
piano stack. Correspondingly, the 5T port activates the fast crescendo
for both the treble and bass sides of the stack.

As a result, there is no need to have perforations present in the 5B
channel on an Ampico B piano roll being played on an Ampico B piano.
However, to ensure that Ampico B rolls could be played 'properly' on
an Ampico A instrument, crescendo perforations were placed in the 5B
channel of Ampico B rolls. Identical perforations were placed in the
5T channel. (In today's parlance, backward compatibility was assured.)
This meant that the 5B tracker bar port could be used for a different
function on an Ampico B piano.

For an Ampico B tracker bar, the 5B port (signal channel) is then
used to activate the shut-off pneumatic (which has a built-in 5-second
delay). This shut-off operation commences as soon as the tapered leader
at the beginning of the roll (near the completion of rewind) 'opens up'
the 5B port on the Ampico B tracker bar. After about 5 seconds, the
complete collapse of the shut-off pneumatic deactivates the piano's
electric power switch. Incidentally, the 1B port on a Ampico B tracker
bar is blank; it is not connected to anything.

The shut-off pneumatic can only be activated if the 'special' valve
(valve 'C') has been turned on previously. This preparatory operation
occurs when the 8T port on the Ampico B tracker bar is opened. The
8T signal (which occurs in the 8T channel near the end of the Ampico
piano roll) also causes the reroll pneumatic to collapse, which puts
the transmission into the reroll mode.

Bill Koenigsberg
Concord, Massachusetts

 [ To be continued ]

 [ Ref. https://www.mmdigest.com/Gallery/Tech/Ampico/amp34.htm
 [ https://www.mmdigest.com/Gallery/Tech/Ampico/amp34c.gif
 [ https://www.mmdigest.com/Attachments/23/02/02/230202_162836_Control_Valve_Block.png