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Electric Reproducing Pianos (The Duo-Art)
(Tuners' Journal - Cont. from February, 1929)

By Wilberton Gould, Member N. A. of P. T., New York City

Service, as defined by Webster: "An act of one who serves."

It is one of God's greatest gifts to mankind, for who is happy who does not serve? Hence it follows that service requires sacrifice. It is the foundation stone of every enterprise. Whatever it may be, its success or failure depends upon whole-hearted co-operation.

And may service and sacrifice continue to be the keynote of our progressive Association.—The Author.

The Duo-Art

The Duo-Art Upright Governor
The Duo-Art governor is extremely sensitive and positive in operation. Reference to illustration "M" on page 35 of the Duo-Art 1927 service manual will show that the atmosphere from the wind motor enters the governor at channel No. 6, passes through channel No. 3, provided the tempo port is open to ten or more, through knife valve port No. 5, and out through channel No. 8 to the pump. Spring No: 9 is the opposing suction in the governor pneumatic. Figure No. 3 is the tempo port, No. 2 is the tempo control slide valve, No. 4 is the reroll port and No. 7 is the reroll slide valve. Figure No. 1 is a bleed channel connecting with the outside air. Its function is to prevent the wind motor from creeping when the tempo is at 0, but this channel is cut off when the tempo is advanced three or four points. Adjustment of the governor will be taken up later under the caption "Testing."

In the grand Duo-Art the governor is Practically the except that the action cut-out is in the modulator box underneath the bed next to the rotary pump, and its function will be discussed under the heading "Duo-Art Grand Modulator Pneumatic."

Sustaining and Hammer Rail Lift
The entire layout of the tubing and control of the sustaining pedal and the hammer rail lift will be found in illustration "N" on page 37. There are three valves in the sustaining pedal valve chamber and two in the hammer rail valve chamber. Those who are familiar with the Duo-Art since its inception will readily see the advantage of this arrangement over the older model.

Quietness of operation is highly desirable, and it is obtained through the medium of the multiple valve control in conjunction with the pressure regulator. A knife valve and a regulator spring are attached to the pressure regulator pneumatic. Adjustment of this spring will control the action of the sustaining pedal, the accordion pneumatics and the hammer rail lift as regards snappy action and quietness. The sustaining pedal and the hammer rail are also controlled through the stop buttons, figures 2 and 3. Too great a tension on the regulator spring No. 1 will cause noise and valve clatter, and too little tension will produce sluggishness of the action. In this unique control it will also be noted that there is regulated and unregulated atmosphere.

In the upright Duo-Art, in conjunction with the soft pedal or hammer rail lift is a pallet valve (not illustrated) whose function is to collapse No. 2 accompaniment accordion pneumatic on the expression box to compensate for the lost motion created by the hammer rail lift. In the grand model the sustaining and hammer rail lift pneumatics are controlled from the modulator pneumatic, and perform the same duty as stated above.

In illustration "0", page 38, are shown the tubing layout, valve control and the position of the repeat slide valve block of the upright Duo-Art, located on the left side of the roll box. In this illustration the switch valve block is mounted on the righthand side of the case, and shows the pneumatic and the valve box as a unit. In the grand model, the switch unit and the switch pneumatic are separate units, but the principle remains the same, no matter how the units are assembled.

Grand Duo-Art Modulator Control Pneumatic
The modulator control box (illustration "P," page 41) is shown only in the grand model and only in instruments of late manufacture. Its function is to modify, or soften, the normal Duo-Art without affecting any of its dynamic gradations. It also controls and, regulates the supply of atmosphere to the accordion dynamics and the sustaining pedal and contains the cut-off valve which cuts off the top action on reroll. A pallet valve block is situated underneath the key bed at the front left-hand end of the case and is connected with levers marked "Concert," or normal, "Soft," orS dance. This pallet valve block is known as the dynamic valve block, and is made up of two pallet valves, with four nipples on the later types and three on the older types. When the dynamic lever is at the "Soft" position the pallet is opened, and atmosphere is admitted to the valves of the hammer rail and No. 2 accordion pneumatic on the accompaniment side. Through another nipple atmosphere is also admitted to valve No. 10, which raises and forces the air entering chamber No. 13 to pass through the knife valve port No. 17 and cuts down the dynamic power of the expression one-half. When the dynamic lever is at the "Concert" position it has no effect on the modulator control box, but collapses the accompaniment accordion pneumatic No. 8, so that the softest power of expression is power eight.

Attached to the grand governor tempo control box and to the grand modulator control box are two small pneumatics, one ( No. 14) on the modulator box and the other on the governor box. Pneumatic No. 14 on the modulator box collapses and opens port No. 3 on the modulator box, and is a pump relief on reroll when these two pneumatics are teed together.

The spring No. 20 on the modulator is set correctly at the factory, and set so that the degree of modulation is one-half the full volume of the Duo-Art. This will correctly control the action of the accordion pneumatics on the expression box and the action of the sustaining pedal. This spring should not be tampered with. Should it be necessary to get at valves Nos. 10 and 5 on the modulator box, this may be accomplished by removing the lower cap, where slide valve No. 4 is situated, but as these valves are of considerable size this occasion seldom arises.

Grand Crash Unit
While the expression box of the grand is constructed somewhat differently from that of the upright, on account of the different designs of the pianos, there is no difference in the principles of the expression control. The grand expression box has a crash valve unit which acts only when power fifteen comes on ; that is, when all of the accordion pneumatics on the theme or solo side are collapsed. The action of the crash valve gives a direct passage to the pump, and when the crash comes on it cuts around the theme knife valve direct to the pump and in this way causes the maximum hammer blow.

When setting the crash valve all theme pneumatics should be collapsed, valve arm No. 6 (see illustration "R," page 45) should be up, and the adjusting screw in the arm should just raise pallet valve No. 5. Should it fail to do so, one or two turns of regulating screw No. 6 should be sufficient. Rough adjustments may be made with regulating screw No. 7 and fine adjustments with screw No. 6. Care should be exercised that the upward travel of arm No. 7 is not so great that it will act when power fourteen comes on ; in others words, the pallet valve should not rise more than one-sixteenth of an inch.

Key Frame Shift
As previously stated, the key frame shift (illustration "S") is installed only in the grand Duo-Art and only in the later models, but in conjunction with the hammer rail lift this attachment permits very fine shading of the music. The key frame shift operates only when No. 1 treble end port is open. There is a separate valve box for this unit located in the rear of the case near the sustaining pedal pneumatic. Lost motion of the shift unit may be controlled by adjusting screw No. 6 on arm No. 5. This unit is silent, powerful and positive in action.

(To be continued)

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This page was last revised March 9, 2021 by John A. Tuttle, who Assumes No Liability
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