Just picked one of these up today with the voltage selector damaged. The trnasformers have two, centre tapped windings. One side is 110V and the other is 10V. With a pair of transformers and the voltage selector, they are wired and combined in a number of ways to "absorb the input voltage. For example, for 240V they are all wired together and the voltage selector jumpers the two transformers together. so, 110 + 10 + 100 +10 = 240.
Hope the helps.