When
studying Wilson's machine (right) I
noticed that one of its plates (the rightmost in the drawing) is just a
contact point,
and that the central accumulator plate is not necessary. Without these
plates the machine is just a different version of Bennet's
doubler,
with an interesting mechanism. The other mechanical versions of
Bennet's doubler that I had made all moved the disks laterally, what
causes charge accumulation at the sides of the disks and prevents the
achievement of very high voltages, due to sparking caused by the
intense lateral electric fields. A machine built in this way moves the
disks almost along their axles, and should be less sensitive to
excessive charge accumulation at the edges of the disks. This
mechanical construction also differs from the others because there are
no moving contacts. A rotating version of the
same idea resulted in
other doubler that I made some time before, that works quite well. So,
by July 2007 I built a version of this "simplified Wilson's machine". I
used three large disks, with 20 cm of diameter, made of plywood covered
with aluminum tape, supported by acrylic rods, and with contact posts
and other elements made of brass. The base was made of plywood, and the
levers of wood. I added also a double ball electrometer in the top
connection bar, that serves as output terminal. With the large disks I
was expecting to obtain visible sparks at the contacts with the machine
charged. The machine has one fixed disk, corresponding to the leftmost
disk of Wilson`s machine, the two movable disks mounted in the
reciprocating levers, and a cylinder replacing the rightmost disk. The
gounding posts are as in Wilson's machine.
The final machine worked as expected for a Bennet's doubler, self-exciting from discharged plates to full charge in at most 20 cycles. It clearly works better than my other mechanical doublers. The mechanical construction is not very practical at this size, could be more solid, but the machine is still easy to operate. When fully charged, small sparks can really by seen when the plates approach the grounding posts and the cylinder, and are clearly audible. The maximum voltage appears to be something around 20 kV. The square edges of the plates, the presence of the grounding posts close to the disks, the electrometer with small balls, and charge accumulation in the spark shields prevents further increase. I installed just two spark shields. Maybe better results could be obtained with the use of pairs of spark shields, one at each plate on the faces that come close without touching, but this would complicate the installation of the grounding posts.
