Depends. Most of them are autotransformers. In this case, the full winding is used for 220 and it's tapped halfway down for 110. I got my last two for free on CraigsList.
---In Homebrew_PCBs@yahoogroups.com, <keethpr@...> wrote :
Aren’t most of these converters to convert 220 down to 120 ?
International voltage converters are widely available in the states.