1947farmer,
They do make all 3 coils you discribe 6V and 12v with or without the internal resistor.
If you're using a 6V coil with the ballast resistor wired in Series to the coil primary on a 12v system, you could do the same thing by using the 12v coil with the internal resistor eliminating the need for the external ballast resistor.
Mike B
