3-Way Volume Control Switch
and Expression (1926 to end of production)

(Photograph courtesy of Art Reblitz)

Seeburg 3-way switch, used from 1926 through the end of production. This style of knob and nameplate were used for both the first version (with 6 connections on a slide switch) and the second (with 4 connections on a paddle switch), as described in the text. (Seeburg Greyhound #166,043, made in 1928.)

(Photograph courtesy of Art Reblitz)

The expression mechanism for the 3-way switch is similar to the 2-way mechanism, but with an additional pneumatic on the front of the distribution box. This pneumatic pulls on the spring arm of the expression regulator, supplying medium vacuum between the soft and loud levels. Other small pneumatic devices, not shown here, connect the expression holes in the roll to the medium and loud (bypass) pneumatics differently, depending on the setting of the control knob. This example, from Greyhound #166,043, made in 1928, also has a flat spring on the back of the vacuum reservoir, with an adjustment screw accessible without removing the unit from the piano.