Hammond Model A, Manual, Page: 91 / 298

When a playing key is pressed, its nine frequencies are impressed on the nine
busbars of the manual. As there are no wires connected to these busbars, a preset or
adjust key must be depressed before any circuit can be completed. Each preset and
adjust key has nine contacts exactly like those of the playing keys. These keys have
a locking and trip mechanism which allows only one key to be in operation at one
time. The key at the extreme left end of the manual is a cancel key, with no
contacts, which releases any preset or adjust key that happens to be depressed.
The adjust keys, A# and B, are connected by flexible wires, color-coded for easy
identification, to the corresponding nine drawbars. The drawbars slide over nine
busses which are connected to taps on the matching transformer. These correspond to
different intensities of sound as shown by numbers on the drawbars.
The two left groups of drawbars are associated with the upper manual, while the two
right groups work in conjunction with the lower manual. In each case the A# adjust
key controls the left hand group of drawbars for that manual. The nine preset keys,
from C#
to A inclusive, are wired to flexible leads terminating at the preset panel
in the back of the console, where the various tone colors are set up by connecting
each wire to a screw terminal corresponding to the desired intensity of the
harmonic. These screw terminals are located on 9 horizontal bars, each representing
a certain intensity for all wires attached to that bar.
The drawbar busses and the preset panel bars are connected in parallel to taps on
the primary of the matching transformer.
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