Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
Hi Ed,
I believe a common SG is an underlining assumption.  The two 
primarys are wired in series. I do have a movie of a twin coil (its 
called Nick's twin) that showes the two secondaries going into and outof phase.
Gerry R.
Original poster: Ed Phillips <evp@xxxxxxxxxxx>
Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
Hi Steve,
I do believe that the primary keeps them in "proper" phase when 
sufficient energy is still in the primary.  My question was 
addressing what happens once the primary quenches (should be at 
maximum energy in the secondary). I'm thinking that phase drifting 
begins at this moment in time if not before.  I guess I'm assuming 
these two coils are side by side and not a bipolar coil.  Even with 
a bipolar coil, if the center turn is grounded, I dont know if the 
magnetic coupling will keep them properly phased.  Maybe Antonio 
can shed some lite on this.
Gerry R."
   Tesla mentions that when two coils are tuned to different 
frequencies the nature of the spark between them can vary over 
wide limits; he doesn't mention whether they had a common primary 
circuit but I would think the same spark gap would be necessary so 
the discharges occurred at the same time.  I've posted the quote 
here but don't have it handy at the moment. It would be make an 
interesting experiment to play with this.
Ed