small valves and RE: OT

Battery radios in the UK typically used 4 valves : DK92 or DK96 pentagrid frequency changer DF91 or DF96 IF amplfier DAF91 or DAF96 detector diode/1st audio (pentode) DL91 or DL96 audio output. Each had a 1.5V filamanet, excpet for the output pentode which had a 3V filament with a centre tap. The first valves listed had 50mA filaments, the second had 25mA ones. Such sets generally either put all 5 filamenet sections in parallel, running them off a 1.5V battery (often 2 or 4 cells in parallel) or put them in series, running them off a 7.5V battery. I think all of them by this point used self-bias. Possible, although a 7.5V filament is not common. And having 5 signal-stage valves with their filaments in series (giving 7.5V) would not be common either. It would be interesting to know what's going on in this set. Can you get a schematic? Being an American set, it's not in Poole and Molloy :-( It's one of the better electronics magazines available over here. It has some interesting projects, and they've now started making microcontroller source code available for most, but not all, of them. The circuit in question was a pretty standard inverter circuit, running at about 50Hz (not a typo, they wanted to keep RF noise down), feeding a normal mains transformer used in reverse. Looks like it should work with no problems. -tony