Scooterotica

OK, Fair enough - I stand corrected! I've since discovered there were some 12Volt Indian GPs wired with 2 sets of lighting coils in parallel, but most setups these days seem to have 4 coils in series. Using the parallel setup may theoretically mean the engine speed needs to be a bit higher to reach 12Volts, but who knows?
The LDA used stator coils with more laminations, so they were non-standard in the first place, although the wire thickness was similar if not identical to the 6 Volt direct lighting coils. I suspect that with the inefficient selenium plate rectifiers of the 1950s (no silicon rectifiers back then), the system needed all the voltage it could get to allow for the forward volts drop through the rectifier!

Steve J wrote: I've since discovered there were some 12Volt Indian GPs wired with 2 sets of lighting coils in parallel.

Yes I had one in the early 80's. The stator was wound in India as per the Lucas/lambretta concessionaires spec, but the other Lucas components were added over here. The zener never had a dedicated heatsink though as they put it in the cooling air of the intake scoop (all following Indian scoops still had this mounting hole). The difference between this system was like night and day compared to my mates with 6v LI's. Also, the way a stator works, 12v should be obtained at the same revs (probably lower) as 6v was obtained originally.

Re the LDA, I have a 60's scootering book that states that many people converted standard LD's to the same spec by adding the extra coil, in series as you say.