Here's another idea I thought of to speed up solenoids or other
electromagnets, while driving home from the MBSI Band Organ Rally
in Berrien Springs, Michigan.  (A great event, where I enjoyed myself
even more than last year.  Mid-AM really does have more fun!).

Light bulbs and coils behave exactly the opposite when first switched
on.  Bulbs draw a tremendous inrush current for a few milliseconds,
until they light up; coils are just the opposite.  So combine the two
to even things out.

Put a small light bulb in series with the solenoid, and increase
the voltage a little bit -- but not all the way to the sum total
of the bulb's voltage and the "original" solenoid voltage.

When the transistor, relay, or music-roll brush first closes the
circuit, the lamp's filament is cold, and has a much lower resistance
than when it is fully lit.  So it is almost a short circuit and hardly
there.  The magnet coil thus gets almost the full voltage to get the
current flowing quicker.

As the current builds up in the coil, the lamp filament heats up and
starts to glow, which raises its resistance.  Ultimately the solenoid
is pulled in and the lamp is lit up bright, so its normal operating
resistance is holding down the current flowing through the coil.

The bulb should be chosen for its normal operating current, not
voltage.  This current should be equal to or just a little more than
the final holding current you desire in the coil.

Given that current, then the higher-voltage bulb you use, with a power
supply at least equal to the bulb's rated voltage, then the faster your
electromagnet will be speeded up.

Any diode or resistor shunted across the coil should be left just
across the coil, and not also the bulb.

Now, a by-product of this trick -- actually the first thing I thought
of -- is that it can add visual excitement to an electrically played
organ.  Unless you have clear plastic wind chests like 'The Spirit of
San Diego' (which let you watch the valves), nothing really moves in
an organ action, unlike piano hammers or xylophone bars.

But by putting a small bulb and socket in front of each pipe, the pipes
will light up as they play.  Such bulbs are used by the hundreds in
pinball machines and easy to come by in large quantities.

Okay, it sounds a little tacky, but remember these organs are supposed
to play at carnivals!  If you object, just put it on the Trumpet rank,
or those big Bass Trombones.

Anyone try this already?

Mike Knudsen

 [ A power transistor circuit, designed provide current limiting,
 [ can provide the same desirable effect, which is faster current
 [ build-up.  Lots of heat is dissipated, but that's not a problem
 [ usually, and voltage-chopper circuitry can minimize the heating.
 [ That's the trick used in some of the solenoid piano circuits.
 [ -- Robbie