c. The same results can be obtained by connecting the line to a number of
selected taps and leaving the output connected to a given pair of taps, as in figure 2-19.
In actual practice, autotransformers are usually provided with many taps in the primary
as well as the secondary with the result that you have almost unlimited choice of voltage
outputs. The autotransformer becomes, in this way, the basic source of all the supply
voltages needed for operating the many components of a complete x-ray generator.
Figure 2-19. Autotransformer with input selector.
d. A common method of using the autotransformer to supply any of a wide
selection of voltages to the primary of the high-tension transformer, and thus to vary the
kilovoltage applied to the x-ray tube, is to use dual selectors in a circuit like the one
shown in figure 2-20. In the figure, voltage is applied to fixed taps on the primary and
"pick-off" voltages by adjustment of the selector switches that make connection with two
sets of taps. The selector marked "Major" is connected to a series of taps between
which there are relatively large differences in voltage. The selector marked "Minor"
gives you small voltage changes. Usually, there are ten steps on the Minor selector that
give you the same change in voltage as going from one step to the next on the Major
selector. With a combination of 10 Minor and 10 Major steps, 100 different output
voltages are available.