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Electric Reproducing Pianos (The Duo-Art)
(Tuners' Journal - Cont. from December, 1928)

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 conditions under which the Duo-Art operates were discussed in the preceding installment in this series. We will now show how the air travel is changed within the expression box when a theme perforation appears on the music roll, and just what happens when this action takes place.

Referring to the phantom view on page 17 of the Duo-Art service manual it will be noted that figures 16 and 27 are the bass and treble theme secondary valves. They are controlled through the bass and treble theme primary valves located in the valve box on the top action at the left of the tracker box. The theme primary valve box is shown at the right of the expression box on page 17. Figures 29 and 30 are the bass and treble theme valves respectively, and are connected to the secondary valves in the expression box and to the tracker bar. As previously stated, under normal conditions the theme secondary valves are against their top seats, thus compelling- the atmosphere from the pneumatic stack to travel through chambers 20 and 24, through the flap valves 21 and 23, into chamber 22, down through the channel, as indicated by the arrows, and through the knife valve port of the accompaniment regulator, and thence to the pump.

The question arises, How do the secondary valves remain against their top seats ? As stated above, there is a theme primary valve box located on the top action at the left of the tracker box. Under normal conditions, the valves in this box are at rest, or down against their bottom seats. Atmosphere is admitted over the tops of the valves, passes through connecting tubes and inflates the pouches under the secondary valves, thus holding these secondary valves tightly against their upper seats and preventing any passage of air from the pneumatic stack to the theme regulator. The inflation of the theme secondary pouches just mentioned is accomplished by the action of the theme regulator suction which entirely surrounds the top surfaces of both theme secondary pouches. The moment theme perforations appear in the music roll, atmosphere is admitted through the theme ports in the tracker bar to the primary pouches, inflating them and raising the primary valves to their upper seats. This action cuts off the atmosphere which was admitted through the top cups and permits the suction of the theme primary box to exhaust the secondary valve pouches through the bottom cups, causing the secondary valves to drop and thus momentarily open a channel between the pneumatic stack and theme regulator. The opening of this channel is the action whereby the air from the pneumatic stack is changed from the accompaniment regulator to the theme regulator.

The moment one or both of the theme secondary valves drop, since the theme regulator suction is usually of a higher intensity than that of the accompaniment regulator, this stronger suction will draw the flap valves (21 and 23) to their seats and cut off channel 22 from the pneumatic stack. Thus, momentarily, the stack may he entirely cut off from the accompaniment regulator, but only when the stack is opened to the theme regulator. When this occurs, the air from the stack entering chambers 20 and 24 will pass down and over the theme secondary valves and into the channel underneath and directly behind the accompaniment channel (this channel is shown but is not numbered on the phantom view, but is indicated by the arrows from the theme secondaries), through the port shown leading into the theme regulator, and thence to the pump and exhaust.

This condition can happen collectively or singly, as the case may be, according to the cutting on the music roll. It will be rernembered that the strength of the blow is governed by the movement of the knife valve within each of the regulators. This movement is controlled by the collapse of the accordion dynamics, and the theme valves determine the note or notes that are to be accented by accenting any note or group of notes whenever a direct passage is opened through the theme regulator to the pump.

If, as has been shown, the path of the atmosphere can be changed within the expression box, it is then proved that the theme regulator may control every note in the register. While the accompaniment regulator does likewise, the theme may accent any note without interference from the accompaniment regulator and may accent any individual note in either the bass or treble action, thus proving that this mechanism is truly based on a musical principle and that it will reproduce exactly the performance of the artist upon the keyboard of the instrument.

Manual control of the Duo-Art is obtained by means of a system of levers situated on the key control slip of the instrument. Normally, they are used only when a roll other than a Duo-Art is used, and then only with the Duo-Art switch in the spool box at the "Off" position. These levers give the operator direct control over the movement of the knife valves in both the accompaniment and the theme regulators as well as control over the theme valves. Illustration "G" on page 21 of the service manual shows one of the regulators, accordion dynamics and manual control lever. It must be remembered that the levers have a down pull on the heels of the knife valves the same as the accordion dynamics, and that the levers control the movement of the knife valves and the opening of the ports.

The more the levers are moved from their normal position, the greater is the intensity of the suction built up in the regulators and correspondingly the stronger will be the force of the blow of the striking pnuematic.

The theme levers control the movement of their respective pallet valves underneath the key bed, allowing atmosphere to be admitted through the ports of the pallet valves directly to the primary valves instead of through the tracker bar. By the use of these levers it is possible to pick out any single note in either the accompaniment or the theme and accent it at will, which follows the same principle as the cutting of the music roll.

The spill valve, or atmospheric intake, is located in the rear of the Duo-Art expression box. It is properly adjusted at the factory and should not be tampered with. As either the theme or accompaniment regulator intensities increase, this valve begins to close and when the intensity of either regulator reaches the tenth degree it is fully closed, remaining closed from this tenth degree through the fifteenth. Below the tenth degree, it is either closing or opening as the regulator intensities are increasing or decreasing, being fully open when no accordion dynamics are collapsed. This spill valve is returned to its normal position by the action of a coil spring, which should be adjusted just strong enough to give it a positive return motion. If it is adjusted too strong, it may retard the motion of the accordion dynamics and thus affect the normal expression. (See illustration "J" on page 28 for the method of connection and its operation.)

The tracking device shown in illustration "L" on page 32 is simple and positive in action, and when understood correctly is very easy to adjust. It should not be condemned if it fails to operate correctly. It should be remembered that not only this type of tracking device, but every other type, was tested under many and varied conditions and that when installed in the instrument it did its work. The greatest trouble encountered in adjusting any tracking device is lack of knowledge of the principle under which it operates. In adjusting the Duo-Art tracking device the power should be on and the tracker bar covered with a roll. The tempo should be set at zero and the tracker ears moved away from the edges of the paper. The tracker pneumatics should be centered exactly and the top drive shaft at the right of the spool box should be at center of the shifting cam ( figure 8). Figure 1 shows a turnbuckle, which adjusts the position of the cam. This turnbuckle has left and right threads and is supplied with lock nuts, which should always be set tight after the adjustment of the cam has been made.

When the tracker pneumatics have been centered and other adjustments made so that the note holes in the music roll align with those in the tracker bar, the tracker ears should be set. These ears should be so adjusted that they just touch the edges of the paper, and the screws ( figures 2 and 3) should be tight. Under no condition should the tracker ears be bent into position with a pair of pliers. This would not only be bad practice and show a lack of knowledge on the part of the service man, but there would be danger of damaging the ears to such an extent that they might have to be replaced with a new set. Many music rolls have been ruined through faulty and incorrect setting of the tracker cars, and the blame placed on the tracking device. If tracking devices were able to speak what stories they could tell!

(To be continued)

NOTE:

In the same instalment, page 286, second column, third paragraph, appeared the statement : "In the upright Duo-Art model the electric cutout switch port on the tracker bar leads directly to the electric switch pneumatic on the right-hand side of the case." Reference to illustration "0" on page 38 of the Duo-Art service manual will show that the tube leading from the switch cutout, or motor port, goes to the left and passes through the repeat slide block where, if the slide block is in the "Off" position, it connects with the tube leading to the switch valve box (figure 8).

In next to the last paragraph in the same installment, page 290, it was stated that in the later types of grand Duo-Art pianos the soft pedal not only raises the hammer rail but also shifts the action. By referring to illustration "S" on page 46 of the Duo-Art service manual it will be seen that only the shifting of the action is accomplished by atmosphere being admitted through the soft pedal port in the tracker bar, while the raising of the hammer rail is accomplished by placing the modulating lever, on the control strip, in the soft position.

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This page was last revised March 9, 2021 by John A. Tuttle, who Assumes No Liability
For The Accuracy or Validity of the Statements and/or Opinions
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