In the sketch the DC is applied via a 220 ohm resistor (1k would be better), this is what stops the AC being shorted out. You will have to wind a centre tapped secondary. Toroids are a devil to wind. Work out what length of wire you will need for one half of the secondary (perimeter of toroid +20% X number of turns). Make a shuttle that will pass through the centre of the toroid. Get twice the length of wire, fold it in half, wrap it around the shuttle, pass the shuttle through the toroid and off you go (winding both halves at the same time)!!
Frank