I am attempting to reverse engineer a small 1960's vintage power transformer that is employed in a vintage audio amplifier. It contains no marking to indicate operating voltage or current ratings, however I do have several sample transformers as well an an operational example of the amplifier that employs it. I have dissected a sample transformer to determine as much as possible about it's construction to estimate what its actual rating might be. It has three windings, including a single 120V primary winding and two secondary windings consisting of a high voltage winding and low voltage filament winding, which measured 640V and 12.7V respectively unloaded. I counted the number of turns of the low voltage secondary and primary windings, but not the HV since that proved to be impractical given the large number of windings involved, along with extremely thin wire embedded within layers of insulation. The 12.7 volt secondary was found to have 128 turns which implied about 10 turns/volt. Given this, I had assumed the number of primary turns should be in the vicinity of 1200 turns. However, the actual number turns I counted was only 810. Given this turns ratio, the low voltage secondary voltage should have been closer to 19V rather than the measured 12.7V (unloaded). I realize that there are losses in real transformers, however, the disparity in this case seems far to great. Am I missing something obvious here? Using the core area I had measured, and applying the fundamental equation to determine the associated number of primary turns, assuming a flux density of 10,000 gauss, resulted in about 1100 turns. More in line with what I would have expected. I am just considering the transformer unloaded at this time, so secondary copper loss should not be a concern. The primary DC resistance is 41 ohms, and no load current is 31ma. I'm kind of at an impasses now as I can't seem to reconcile the disparity. Any ideas?