Sorry it has taken me so long to respond to this question.  I was
stuck at the theater every night and too tired to dig out my info
on chimes; I figured someone else would post the answers by now.

Most older chime units are AC operated and powered by a multi-tap
low-voltage transformer, typically a five-tap transformer with tapped
voltages at 24 VAC, 20 VAC, 15 VAC, 10 VAC, 5 VAC.  (I have to admit
that I am guessing at the lower voltage; I can't find the specs on
our transformer.)  The tap switch provides a "volume control" for
the chimes, usually by a rotary switch mounted on the organ console,
but sometimes the chime unit has it's own keyboard.

Here's the URL to a modern 21-note chime unit:
  http://www.petersonemp.com/products/pdf/cathedralchimes.pdf

And a link to a solid-state chime relay that will let you operate the
chimes from a low voltage DC system, oftentimes the organ keyboard
itself:
  http://www.petersonemp.com/products/pdf/solidstate.pdf

I would not recommend playing your 24-volt chimes on 48 volts: you're
liable to melt the coil insulation, eventually shorting out the coils.

The other problem that chime units have is cracking tubes, and the
suspension cords rotting or being cut by the edges of the holes in the
tubes they pass through.  If you look at the pictures of the one on
eBay, you can see where someone has repaired the cords by tying them
together.

David Dewey