It does mean that the 4 V winding has double the rated voltage across it, but that is acceptable because the frequency is a lot higher (several kilo-Hertz) than the 50 Hz (60 Hz) the transformer is designed for. The 2×4 V secondary of AC power transformer (Tr1) is used back to front. The power is provided by six C-type batteries, which keeps the total weight at a reasonable level. The TL494 was chosen because it can still operate at a voltage of about 7 V, which means it can keep on working even when the batteries are nearly empty.
The use of a voltage multiplier has the advantage that the working voltage of the smoothing capacitors can be lower, which makes them easier to obtain. P1 is used to set the maximum current and P2 sets the output voltage. The circuit uses common parts throughout a TL494 pulse-width modulator, several FETs or bipolar switching transistors, a simple 1.4 VA mains transformer and a discrete voltage multiplier.
