Transformer help

Ok, the problem is becoming clearer. Your going to have to wind your own transformer. Not much else to do. Here is what I suggest. If you want to start with an AC transformer, again, I recommend the core from a wall wart. These usually have two bobbins. One for the AC Line side and on for the output. Remove the input side winding and wind your new low voltage winding. Use two transistors instead of one as a center tapped push pull. This will avoid saturating the core with a steady DC offset. Drive it with a square wave, not a sinusoidal. You'll be unlikely to get close to 45% efficiency with a sinusoidal drive. Even with a square wave drive, you'll be lucky to get 75% efficiency and such a low voltage input. The output should be a square wave as well. Assuming your getting about 4.5V peak drive the number of turns will be about 0.7 the output turns except it will have a center tap ( 4.5 on each side ). Since the square wave will drive half at a time you'll get your 12V peaks as a 9VAC would have. You'll most likely need a couple snubbers on the collectors of the the transistors. You can determine the number of turns the secondary that you currently have with a low voltage AC source and a few test turns and meter. Dwight