The waveform produced by variations in the output of radiological X-ray tubes during exposure was recorded by a solid state detector and oscilloscope in 14 different systems. Aberrations from the expected rectangular shape were observed in 11 of them, of which, 8 had faults due to bad service or improper installation. In some cases these faults affected the kVp rectification. This resulted in beam quality variations during the exposure which may have caused an increase in the patient dose. The ripple on the output waveform was also measured and proved to depend on the kVp.