Link Music Roll Tune Indicator

(Photograph courtesy of Rusty King)

In this overall view, a wooden drum 4-7/8” in diameter by 3/4” wide carries numbers 1 through 15 on its outside circumference. On the inside edge of the drum side there is a circular row of 15 threaded holes, each with a die-stamped number to identify its relative location. Hole #15 has a small threaded brass pin installed. Inside the circular row of threaded holes in a smaller circular row of 16 pins, one of which does not need to be there. There is a coil spring around the drum’s axle, which is tensioned in a counterclockwise direction. On the left is a pneumatic that is teed into the shut off tubing and that has a horizontal arm attached that advances the drum one number position by pushing on a pin. There is also a flat spring that rides on a raised red fiber ring, which adds just enough drag so that the drum does not jump ahead too far when the pneumatic pushes the advance arm onto a pin. Just to the left of the flat spring is a vertically oriented locking pawl, which is spring loaded, so that it can hold a pin in position when leaning to the right, preventing the drum from rotating out of position, or the pawl can be tilted over center to the left and stay clear of all pins when resetting the unit back to the tune #1 position. Note the small threaded brass pin in hole #15 and the little metal reset finger immediately below it (the reset finger and brass pin above it are located just above the vertical locking pawl).

(Photograph courtesy of Rusty King)

The working side of the tune indicator drum is shown above. Beginning near the outer edge of the drum there is a circular series of threaded holes, each with an adjacent die-stamped number (1 through 15) marking its location. Next comes a smaller circle of metal pins, and then a yet smaller red fiber ring that has a flat metal spring with one end resting on the fiber to keep the wheel from jumping ahead or otherwise jiggling out of position. Lastly there is a center bearing point about which the wheel incrementally rotates. During operation a shut-off perforation in the music roll causes the vertically oriented pneumatic (at left) to collapse, which in turn pushes the attached horizontal advance arm to the right, where the notched end contacts a pin and advances the tune indicator drum clockwise one tune number. At the top of the pneumatic is an adjustment screw with a felt button used to control the travel distance of the horizontal advance arm. The vertical metal spring loaded locking pawl, to the right of the pneumatic, prevents the tune indicator drum from rotating out of position, or it can be swung over center to the left to stay clear of all pins when resetting the unit back to the tune #1 position.

(Photograph courtesy of Rusty King)

In this example, when tune #15 is played (for a 15-tune music roll) the brass pin will be positioned under the vertical locking pawl. When the shut off perforation activates the pneumatic and pushes the advance arm to rotate the drum clockwise the brass pin nudges the vertical locking pawl to the left, whereupon it tilts over center and then stays out of the way of all pins. This allows the coil spring on the drum’s axis to rotate the drum back to the tune #1 position. The brass pin is made of 1/8” diameter brass rod, 1/2” long with a 6-32 thread 3/8” up from the bottom. The top is slightly rounded and has a slot for a tiny screwdriver.

(Photograph courtesy of Rusty King)

With the vertical locking pawl tilted over center to the left and thereby out of the way, the coil spring on the drum’s axle spins the it counter-clockwise to the tune #1 position—almost one complete rotation when set for a 15-tune music roll. Just as pin #1 approaches the vertical locking pawl the reset finger on the drum contacts the top of the locking pawl, thereby nudging it over center to the right whereupon it then catches and holds pin #1 in position. The tune indication is now reset to tune #1. If there was a 10-tune roll in use the threaded brass pin would be located in hole #10, so that the drum would reset from the tune #10 position.