These transformers were actually wound by B&O for some reason,and they are fitted in accordance with the power parameters of the market they were intended for.They cannot be altered for different power voltages as the main transformer can be
Depending upon whereabouts you are,you will need a transformer with twin primary and secondary windings.Eg,for the U.K. you would need two 115 windings wired in series for 240v main power,and secondary windings producing about 28 volt per winding.The subsequent supply only supplies the stand-by voltages +15-15,and the stand-by relay circuit,so not much current is needed.
Some reworking of the connections will be needed too of course.
A variety of suitable transformers are available,but don't undertake this work if you are not experienced,as you could end up in a cloud of smoke!!!
Nick