Some original era instrument builders were concerned with electrical
safety, and enclosed their 110 VAC wiring in flexible conduit.  Sometimes
the old wiring cannot be pulled out of this for replacement because the
insulation inside is rotten.

Large electrical supply houses have a product called '3/8-inch Greenfield'
which is a suitable replacement.  I replaced all the power wiring in my
organ console, which was just tacked to the wood, with this; as others
have said, authenticity can take second place to safety in such matters.

In equipment operated by DC magnets, the primary source of arcing at the
contacts is not the power source voltage arcing across the contact as it
is being closed, but rather the energy stored in the 'closed' magnet being
dissipated across the gap in the contact as it is opened at the end of the
'stroke'.

When the spring pulls the magnet open after the power is removed by
opening the contact, the system acts as a generator, producing a voltage
in the opposite direction, which must be as large as is necessary to arc
across the partially opened contact.  Even a tiny pipe-organ magnet can
generate a back voltage that can produce an uncomfortable zap if you hold
the wire, even though the operating voltage is only 15 volts in the
forward direction.

All modern DC magnet circuits use a 'clamping diode', wired backwards in
parallel with the coil.  When the coil is powered, no current passes
through it, but during the de-energizing phase, the back voltage generated
by the field collapse flows backwards through it, reducing the spark or
surge through the contact or actuating transistor very considerably.

It is customary to add these to pipe-organ magnets and switch coils,
which lengthen the life of the key contacts and switch wire contact
points very considerably.  Is it customary to put these in a Violano?
Considering the huge magnets used, it would seem to be a good idea.

Early people recognized this problem, but had no diodes.  They sometimes
put a resistor in parallel to the coil; this works after a fashion, but
wastes power, since extra current flows forward through this resistor
during the actuation phase as well.  For large DC magnets which can
generate tremendous back voltages, the diode would have to be big,
probably a 1000 volt, 3 amp 1N5408.

Richard Vance

 [ Oops -- the insulation will probably rupture before 1000 volts is
 [ reached !  A simple diode which shunts the coil need only withstand
 [ the battery voltage, e.g., a 50-volt diode is adequate when used
 [ to shunt a 15-volt magnet coil.
 [
 [ However, the shunt diode slows the current decay, hence the
 [ release of the armature, and so may cause undesired sluggishness.
 [ Shunt "clamping" diodes added to the piano-action magnets in the
 [ Violano don't slow the release significantly, but they sure reduce
 [ the sparking at the paper!  -- Robbie