Oops, I found the edit pencil. Pls disregard my comment. A bit on the "American 5 tube radio". Well, as I said previously, 3 tubes were needed to process the RF.  The third tube actually has a diode to it     and so the audio is pre-amplified by the 3rd tube. The fourth tube is the final audio amp. Then one more tube to act as the rectifier to convert AC to DC voltage to operated the tubes.

When I see a tube radio with a transformer, it means the tubes' heaters are not in series. I eliminate the heater tube and just use a silicon diode.