Heckel (95 III) / Fox 12

Ab+Bb-trill mechanism without extra tonehole

How: Low-G-key automatically closes Bb-tonehole if Bb-key is engaged.

Ab+Bb trill: w ● ● ● / Bb ● ● G# or / Bb ● ● G#

Ab+Bb-trill possible without using a special key.
Facilitates tremolos between Bb and low-G, -F# (R-4f), and -F.

G-key action is relatively heavy when Ab+Bb-trill mechanism is engaged.
High-D may not be played with the Bb-key (R-t) unless this mechanism is disengaged.