Hammond Model A, Manual, Page: 130 / 298

(e) It inserts resistor RI in series with upper manual matching transformer (T2)
secondary to reduce upper manual organ signal so that lower manual will musically
balance with the combined upper manual organ and percussion signals.
The Preset Percussion Switch is not part of the control tablet assembly or
percussion on-off tablet, but functions as an interlock with it. It is located under
the upper manual B adjust key. This switch insures that the full upper manual
signal is restored by shorting out series resistor R1 introduced by the percussion
on tablet when any other upper manual preset or adjust key is pressed. The Volume
Tablet in soft position shunts resistor R46 across the percussion output
transformer, reducing percussion signal, and also shorts out upper manual matching
transformer compensating resistor RI thus restoring upper manual signal strength to
provide proper balance between the manuals.
The Decay Tablet in fast position shunts resistor R57 across the slow decay
resistor (R58) reducing time for decay capacitor C31 to discharge and for V7 control
grids to reach cut-off. Also to preserve the same effective loudness in fast decay
position as in slow decay the control tube bias is reduced by disconnecting R59 and
allowing control
tube grids to become more positive which increases output signal
about 50%
.
The Harmonic Selector Tablet does three things to the signals of the upper manual
B adjust key drawbar group:
In Second Position:
(a) It connects the 2nd harmonic signal wire to percussion amplifier input.
(b) It connects the 3rd harmonic signal wire to the 3rd harmonic drawbar.
(c) It connects the signal from terminal J to 2nd harmonic drawbar.
In Third Position:
(a) It connects the 3rd harmonic signal wire to the percussion amplifier input.
(b) It connects the 2nd harmonic signal to the 2nd harmonic drawbar.
(c) It connects the signal from terminal J to 3rd harmonic drawbar.
The Percussion Cut-off Control which is located on the amplifier should be re-
adjusted as follows whenever control tube V7 is replaced:
Set expression pedal wide open, both volume tablets normal, percussion on,
percussion decay fast, and harmonic selector in either position. Depress any key in
upper half of upper manual and then adjust cut-off control exactly to the point
where signal becomes inaudible.
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