Hammond Model A, Manual, Page: 92 / 298

Manual Chassis Assembly - Models B-2, C-2 and RT-2
In these selective vibrato consoles, the individual manuals are the same as in other
models but the drawbar assembly is different, having three tilting tablets (Vibrato
Swell On-Off, Vibrato Great On-Off and Volume Soft-Normal) at the left of the
vibrato switch knob.
The selective vibrato feature requires that the preset panel and drawbar assembly be
divided and connected to two matching transformers, each serving one manual. See
Diagrams & Schematics section. The Great, or lower manual, matching transformer also
serves the pedal keyboard.
Continuous-contact drawbars are used in later consoles of this type. They operate
more smoothly and require less accuracy of adjustment than the earlier type having
nine definite positions or steps. Each one has two contacts connected together by a
one ohm resistor, so that at least one of the contacts touches some bus at all times
and there are no dead spots in the drawbar motion. The resistor avoids short-
circuiting adjacent busbars.
Manual Chassis Assembly - Models B-3, C-3, RT-3, A-100 & D-100
The above description also applies to these models, but the start and run switches
are relocated to provide room for four tilting tablets which control the Percussion
feature, described in Section 2. All manual chassis assemblies are equipped with
continuous contact drawbars.
Manual Chassis Assembly - Model E
The appearance of the upper, or swell manual, and the lower, or great manual, is the
same as on other models except that numbered pistons are used instead of preset
keys. These pistons operate in exactly the same manner, and produce the same
effects, as do the preset keys on the other models.
The internal wiring of the manuals is to a large extent the same as in other models,
but the use of two tremulants requires that the preset panel and drawbar assembly be
divided, and that two matching transformers be used, each manual being connected to
its own matching transformer.
Manual Busbar Shifters
The precious metal contact surfaces of the key contacts and busbars are not subject
to corrosion, and the manuals are sealed to exclude dust as far as possible. In
spite of these precautions an occasional particle of dust many lodge on a contact
and cause the note to be scratchy, noisy, or silent, and for this reason a busbar
shifting mechanism is provided on each manual to slide the busbars endwise and thus
provide a fresh contact surface. The busbar shifter for each manual is a slotted
stud near the right end of the manual as viewed from the back of the console (see
rear view of console in Section 2 for location).
If any note becomes scratchy or silent, it should first be struck 15 or 20
times in a rapid staccato manner to loosen the dirt. This will usually dislodge
the particles and clear the note.
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