3. FOUR PERCUSSION CONTROL TABLETS, CUTOFF CONTROL, AND THEIR FUNCTIONS.
The Percussion On-Off Tablet when turned "on" does five things to the signals of the upper manual "B" adjust
key drawbars.
(a) It disconnects the 2nd harmonic drawbar from its signal wire.
(b) It disconnects the 3rd harmonic drawbar from its signal wire.
(c) It connects the 2nd or 3rd harmonic drawbar signal wire (depending on position of Percussion Harmonic
Selector Tablet) to input of percussion amplifier.
(d) It disconnects the 8th harmonic drawbar from its signal wire. This wire (which will be connected through
generator filters to ground when any key is pressed) is connected to terminal K. The 8th harmonic signal is
not available on the upper manual as long as the percussion tablet is "on".
(e) It inserts resistor R1 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 them. 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
the percussion signal, and also shorts out upper manual matching transformer compensating resistor R1
thus restoring the 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 controls 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 the 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 the 3rd harmonic drawbar.
The Percussion Cut-off Control, which is located on the pre-amplifier, should be readjusted 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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