In a message dated 11/20/03 3:17:06 AM Eastern Standard Time,
rolls@foxtail.com writes:

> A J Omega Electronics MTP-1 32-note (plenty of room for expansion) has
> been purchased and will be used to drive solenoids to actuate the keys
> and valves.  The problem here is the solenoids draw 0.7A, and as the
> rated output from the MTP is only 0.5A, either amplification or relays
> will be required.  Short of purchasing new solenoids, are there any
> suggestions?

You've gotten off to a proper start, buying the J-Omega board -- good
stuff.  Relays will work as amplifiers, and are fun to watch, and are
more in keeping with steam technology, but they are expensive, bulky,
and trouble-prone.  You can buy so-called "tab" power transistors
cheaply and easily, which will drive your solenoids directly.

Since the jW board operates its outputs by shorting positive voltage
to ground, you want PNP (not NPN) power transistors.  Each transistor
needs a series resistor between its "base" and its jW output.  The
valve solenoid can be connected through the emitter or collector of
the transistor.  In either case you must put a "snubbing" or "kickback"
diode across each coil.

With careful planning and bending and shaping of component leads with
a needle-nose pliers, you may be able to mount the 3 components for
each note right on the solenoids terminals, and run the drive wire to
the jaw board.

Enjoy marrying up 18th and 21st century technologies!

Mike Knudsen