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After posting a request for information about the 'Half' Duo-Art player system, I received the pictures and email below. What I find interesting, and a bit mysterious, is the pallet valve that gets actuated by the armature that's connected to the knife valve rod, which protrudes from the side of the expression device. In the system I dismantled, a similar pallet valve is connected to the Soft Pedal pneumatic, which gets activated each time the bellow collapses. Here again, it's function is unknown at this time. Hopefully, I'll be able to find out the purpose of these pallet valves. Part of the mystery seems to have been solved by Randolph Herr. He wrote:
comments: I think that I can help John Tuttle with the mystery pallets on the Half Duo-Art, (which may sound like it should be a Single Art, but let's not quibble). Aeolian would always make their foot-pumped systems so that if you were to raise the Accompaniment level to the highest point, it would automatically turn on the Theme, but only at that point. There cannot be a pallet like this on electric Duo-Arts, although the electrics do have a different pallet on them. On these pianos, when the Theme gets to its highest level, a pallet is turned on to allow a larger volume of air to flow through the mechanism, so that crashing chords will sound better. Getting back to John's question, the reason there is a pallet valve on the soft pedal is that regardless of whether the piano is manual or electric, the softest chords will miss when the soft pedal is activated. I am pretty sure that the pallet here goes to the second Accompaniment level, although the owners can easily change his if they want. There is one more type of soft pedal control that I have found only on the Steinway and Weber Uprights that were foot pumped. I call this the "Analog Temponamic Soft Pedal" and it is too complicated here to try to do justice to this ingenious mechanism. Fortunately, I have a Steinway Upright with this mechanism, and I will write a separate article about this thing, and include photos also. (Submitted by Randolph Herr)
Subject: Half Duo-Art Mystery Pallet Valves
Here is my answer to the role of the pallet valve in the pedal-only Duo-Art system.
My London-built instrument has a pallet valve mounted on the expression box just above the Duo-Art accordion pneumatic. When the dynamic level reaches 11 or thereabouts the pallet valve is pushed open by the regulator arm. This lets air into a pair of tubes which are teed into the tubes running from the tracker bar to the Bass and Treble theme primary valves.
In other words, the pallet valve ensures that above a certain accompaniment level, all notes are played at the Theme level, which is set by the suction supply provided by the pianolist via the foot pedals. Presumably this was meant to protect pianolists from having to produce massive suction levels to provide a theme level audible above a loud accompaniment. But losing any possibility of themeing can't really help the music!
Hi John, I just read the MMDigest from May 5th regarding Half Duo Art. My piano is Half Duo Art. It does not function properly as this section has not been redone. When its time to start work on it, probably during next winter, I will try do make some more detailed pictures and draw a schematic of the tubing. On the last picture You see lots of space, thats where the suction box will be installed. Before my time, somebody has already made a hole in the back wall. The pump is now waiting to be installed. It's working well and the adjustment of the vacuum does also work. Best regards Hans J. Schweizer Switzerland
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