The main ingredient is this:
The voltage rating of the transformer on the input side determines for which mains voltaeg the circuit can be used. For 110V operation you obviously need a 110V/14V transformer.Transformer that has an output of 14v - 35v AC with an output current between 100mA to 1A, depending how much power you will need. (I found a 16v 200mA transformer in a broken alarm clock.)