The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want.
http://home.cogeco.ca/~rpaisley4/x1Tran2Throt.html
How those little things convert mains AC to safe low voltage DC
http://www.howstuffworks.com/inside-transformer.htm
A method to determine the Linear Transformer Model parameters of a Neon Sign Transformer
http://hot-streamer.com/TeslaCoils/OtherPapers/TeroRanta/CurrentLimitedTransformers/NSTModel.htm
How to test that transformer.
http://home.earthlink.net/~jimlux/hv/xfmrmeas.htm