|The photograph shows the regulator, a
"T" shaped tube attached to the bulb of the X-ray tube. Inside
the regulator is a bundle of asbestos fibers, wrapped around the
asbestos is an iron wire, connected to the terminals shown. To regulate
the tube a 12 v battery is connected to the terminals, and the asbestos
heated up. This releases gas entrapped in the fibers, which lowers the
This process would need to be repeated about once per week in a busy department, if the working kV was to be kept within reasonable limits.