Hello Brian.
I have not worked on Wurlitzers but I was interested in your
problem.
OK, so the fault is common to both manuals but not pedals. How
is the manual keying done on a 630. Is it done by diode switching?
The first thing I would do is look around the keyboard and find the source of
the keying voltage. From your description I would say the noise is on
there. Just another thought. Wurlitzer???? Immitation theatre organ???
Does it have any kind of Brush/cymbal white noise generator in the organ.
These trigger from the keyboards and if not set correctly can give a continuous
noise rather than a brief pulse. Some white noise is also added to snare
drums.
As you have the drawings, you should be able to locate which
section of the organ is sending this noise to the pre amp.
Good luck. Let me know how you get on.
JohnB