Figure 3 shows a power transformer with three secondary windings. The top winding has many more turns than the other two. This top winding is the high voltage winding of the transformer. The bottom of the high voltage winding goes to ground. The top of this winding goes to the plate of a filament type diode. above the lead from the transformer to the tube is a wave indicating a normal sine wave on this lead. Each side of the filament connects to its own side of the middle winding on the transformer. One side of the filament connects to a resistor. The other end of the resistor connects to the bottom of the high voltage winding and ground. A wave form indicates that the voltage across the resistor consists of only the positive halves of the sine wave. When the sine wave at the plate of the tube is negative, the output wave stays at zero. The third winding is not shown connected to anything but it is the 6.3 volt supply for the tube heaters in the rest of the device.