Purely solid-state controls (i.e., a large transistor per note) may
be adequate.  But for really BIG coils (such as I saw on a Deagan
instrument once) you may be safer to borrow a technique from the auto
industry by way of the Pinball Machine industry.

Use an automotive horn relay for each note.  These are quite small
these days and probably very cheap compared to the rest of the
instrument.  Each relay has four tab terminals for quick disconnection
and replacement.

Use a small "tab" power transistor to drive the relay coil, with a
diode across the coil.  Then let the relay's contacts drive the Deagan
coil with whatever voltage is appropriate.  The contacts will last
longer if you put a diode across the Deagan coil too (this was discussed
to death a few months ago).

Note that most gadget coils on a pinball machine are driven directly by
power transistors.  But there are a few very powerful kickers and
ball-grabbing magnets under the play-field, that are driven indirectly
through the horn relays.

One disadvantage is that the relay is on or off, and can't be
"modulated" to vary the intensity of the stroke.  Of course you could
control the master voltage fed to the coils, just as an expression
piano controls the vacuum.

And don't forget your earplugs while debugging the setup.   :-)

Mike Knudsen

 [ A relay is affordable for a few circuits, but is nonetheless
 [ usually more expensive than a suitable semiconductor.  The
 [ electronics in the pinball machine were probably built for
 [ the _average_ coil, and a few relays added for the special
 [ situation.  In contrast, Steve Goodman is faced with a new
 [ design for 48 solenoids.  -- Robbie