[mikethedruid]

Correct me if I'm wrong, but I seem to remember that the impedance which the tube plate circuit sees is a function of the winding ratio and the speaker voice coil resistance. In other words, if the transformer ratio was 200 to 1, primary to secondary, and the voice coil was 8 ohms, the impedance reflected to the plate circuit would be approximately 8 x 200, or 1600 ohms. For the transformer Terry linked that would work out to a turns ratio of about 625 to 1.