[Arran]

What I could never understand about many of these transformerless sets is that they were designed for AC/DC only. Like the schematic for the Pilot that Tom linked to, it has a pair of 25Z5s connected in parallel, when they could have been hooked up as a voltage doubler. Of course with four output tubes the current draw will be higher, but if they used a voltage doubler they could get more performance without having to use 25L6s in Push-Pull parallel. There were also some strange Halson and FADA models that were transformerless but with high tube counts, but again they made them AC/DC only.
The strange part is that the 25Z5, and it's 25Z6 successor, was intended to be used as a voltage doubler but I've never seen them used in that way, though I have heard some odd sets did. For some reason they made most of these sets to accommodate the minority of DC only power grids, a few minor circuit changes and they could have made a high performance transformerless AC design. With some thinking they could have made a change over switch so they could be converted back and fourth, kind of like the voltage changing taps on a European export radio.
Regards
Arran