A constant voltage rectifier is normally adjusted by changing:

Adjusting a constant voltage rectifier typically involves changing the secondary transformer taps. This is because the output voltage of the rectifier is determined by the transformation ratio of the secondary winding of the transformer. By using different taps on the secondary winding, you can alter the voltage supplied to the rectifier, enabling you to maintain a stable output voltage regardless of variations in load.

In contrast, primary transformer connections primarily affect the input voltage and not the output directly. Adjusting the load on the rectifier can change the output voltage, but this is not a method used to set the rectifier output to a constant voltage under varying conditions. The type of anode used is more relevant to the overall efficiency and performance of the cathodic protection system rather than adjusting the rectifier output itself. Therefore, changing the secondary transformer taps is the most effective and common method to adjust a constant voltage rectifier.