The sound optical system used is similar to that described and illustrated in
section 90 and Figure 64. Lateral, horizontal and focusing adjustment screws are
provided, as with the other types, and the exciter lamp has a vertical adjustment,
described in section 278.
The standard Photophone UX-868 Photocell is used in the portable projector.
In the illustrations it is shown covered by a metal shield, which protects it from
extraneous light. The light beam from the optical system passes through a hole in
the shield onto the cell after passing through the sound track on the film. The
photo-cell terminals lead to an input transformer located in the projector, and this
is connected by a cable to the amplifier.
The exciter lamp operates at 27 volts, 1 ampere and derives its direct current
from a Rectox rectifier in the amplifier. The exciter lamp current is controlled
by means of a rheostat (See Figure 136). It is possible to burn out the exciter lamp
if the rheostat is not properly set. It is, therefore, important that the knob be set to
the extreme counter-clockwise position before the amplifier power is turned on.