Another type of rectifier is used to supply DC power for the field of the loud speakers. This
type of rectifier is called a "Rectox."
135. Rectox Rectifier.-The Rectox rectifier used on RCA Photophone equipments is shown in
Figure 95. This rectifier is different from rectifiers previously
described in that no tubes are used. The Rectox unit consists of discs of copper coated on one
side with copper oxide. Many such discs are clamped together with small lead discs or
spacers between them, this spacer being located between the copper side of one disc and the
copper oxide side of another. The purpose of the lead is to make a firm contact over the entire
surface of each side of the disc. The softness of the lead allows it to "flow" slightly so that it
makes contact with all points on the disc and prevents injury to the copper oxide coated
surfaces. The large plates of metal shown in Figure 95 are for cooling, the large area which
they expose to the air effectively dissipating the heat generated in the unit.
Four such units are connected together as shown in Figure 93. It depends for its operation on
the fact that current will flow through such a "stack" of oxide coated copper discs in one
direction only, that is, from the copper oxide to the copper. A study of the diagram shows just
how this fact is utilized in changing AC to DC without the use of any moving parts or vacuum
tubes. The arrows show the direction of the current through the circuit. When the AC voltage
is in one direction the current flows through one half of the units, and when it is in the other
direction the current flows through the other half. The full arrows show the direction of the
current through the circuit when the AC "Line A" is positive and "Line B" is negative. The
dotted arrows show the direction of the current
through the circuit when the AC "Line B" is positive and "Line A" is negative. In this way AC is fed
into the unit, and DC is taken out of it.
The condenser across the DC output filters out the pulsations of the DC voltage. The speaker field
winding, being highly inductive, aids in smoothing out the pulsations.