Robbie Rhodes wrote:

>  ... the Unaphone coil resistance measures 2.2 ohms when cold, so at
> 6 volts it draws 2.8 amperes, and at 12 volts (Heavens!) it draws 5.6
> amperes.  That's much, much more current than drawn by organ magnets
> and the solenoids in modern solenoid pianos.  A chord of 10 notes
> draws more than 50 amps from the power source!

I passed this clip on to a friend who restores pinball machines and is
building his own pipe organ, and has built headlight controls for
touring motorcycles.  He states that power MOSFETs are the ideal device
for this application.  They can switch up to 20 amps and sustain a
5-amp current, with under 0.1 ohms of resistance when turned fully on.
Yet their control gate input is high impedance and requires almost no
power to control.

While a 10-note chord could draw 50 amps (through 10 MOSFETs), the
strikers are pulsed for only a short instant, so a more modest power
supply with a very large electrolytic capacitor (or auto battery)
should do the job.

Robbie, are these the type of devices you plan to use?

Mike Knudsen