The filament current is controlled by the technologist through a device called a:

The filament current in an x-ray tube is essential for generating x-rays, as it heats the filament to produce a thermionic emission of electrons. The device that controls the filament current is the rheostat. A rheostat is a variable resistor that allows for the adjustment of current flowing through the filament, enabling the technologist to change the temperature of the filament. This, in turn, alters the number of electrons emitted and ultimately affects the quantity of x-rays produced.

Using a rheostat provides the technologist with precise control over the filament current, allowing for adjustments based on the specific imaging needs and desired exposure parameters. By changing the resistance in the circuit, the technologist can increase or decrease the filament current to optimize the x-ray production process.

In contrast, an autotransformer is primarily used to adjust the voltage in the main circuit, a circuit breaker is designed for safety to prevent overloads, and a rectifier converts alternating current to direct current, none of which directly control the filament current.