The Recent Revolution in Organ Building | Page 9

by scientific calculation, recognized the value of low voltage, good insulation and the avoidance of self-induction, with the result that the electro-pneumatic action has become (when properly made) as reliable as the tracker or pneumatic lever mechanism.
DESCRIPTION OF THE ELECTRIC ACTION.
The electric action consists substantially of a small bellows like the pneumatic lever, but instead of the valve admitting the wind to operate it being moved by a tracker leading from the key, it is opened by an electro-magnet, energized by a contact in the keyboard and connected therewith by a wire which, of course, may be of any desired length. We illustrate one form of action invented and used by Hope-Jones.[5]
Within the organ, the wires from the other end of the cable are attached to small magnets specially wound so that no spark results when the electric contact at the key is broken. This magnet attracts a thin disc of iron about 1/4 inch in diameter, (held up by a high wind pressure from underneath) and draws it downward through a space of less than 1/100 of an inch.
The working is as follows: The box A is connected with the organ bellows and so (immediately the wind is put into the organ) is filled with air under pressure, which passes upwards between the poles of the magnet N. Lifting the small iron disc L it finds its way through the passage L into the small motor M, thus allowing the movable portion of the motor M to remain in its lower position, the pallet C|1| being closed and the pallet C|2| being open. Under these conditions, the large motor B collapses and the pull-down P (which is connected with the organ pallet) rises.
[Illustration: Fig. 6. The Electro-Pneumatic Lever]
When a weak current of electricity is caused to circulate round the coils of the electro-magnet N, the small armature disc J is drawn off the valve-seat H on to the zinc plate K.
The compressed air from within the small motor M escapes by way of the passage L, through the openings in the valve seat H into the atmosphere. The compressed air in the box A then acts upon the movable portion of the small motor M in such a manner that it is forced upwards and caused (through the medium of the pull-wire E) to lift the supply pallet C|1| and close the exhaust pallet C|2|, thus allowing compressed air to rush from the box A into the motor B and so cause this latter motor to open and (through the medium of the pull down P) to pull the soundboard pallet from its seat and allow wind to pass into the pipes.
[Illustration: Fig. 7. Valve and Valve Seat, Hope-Jones Electric Action]
The valve-seat H has formed on its lower surface two crescent shaped long and narrow slits. A very slight movement of the armature disc J, therefore, suffices to open to the full extent two long exhaust passages. The movement of this disc is reduced to something less than the 1/100 part of an inch. It is, therefore, always very close to the poles of the magnet, consequently a very faint impulse of electricity will suffice (aided by gravity) to draw the disc off the valve-seat H. The zinc plate K being in intimate contact with the iron poles of the magnet N, protects the latter from rust by well-known electrical laws. All the parts are made of metal, so that no change in the weather can affect their relative positions. R is the point at which the large motor B is hinged. G is a spring retaining cap in position; O the wires leading from the keys and conveying the current to the magnet N; Q the removable side of the box A.
Fig. 7 represents a larger view of the plate K in which the magnet poles N are rigidly fixed--of a piece of very fine chiffon M (indicated by a slightly thicker line) which prevents particles of dust passing through so as to interfere with the proper seating of the soft Swedish charcoal iron armature disc J--of the distance piece L and of the valve seat H.
On the upper surface of this valve seat H another piece of fine chiffon is attached to prevent possible passage of dust to the armature valve J, from outside.
As all parts of this apparatus are of metal changes in humidity or temperature do not affect its regulation.
The use of this action renders it possible for the console (or keyboards, etc.) to be entirely detached from the organ, moved to a distance and connected with the organ by a cable fifty or one hundred feet or as many miles long. This arrangement may be seen, for example, in the College of the City of New York (built by the E. M. Skinner Co.),