Hi Jolyon,
> I have not yet read Paul Nicholson's work
Don't bother. I haven't written anything on this topic,
except in a few list posts which I wouldn't recommend you
try to find. I can summarise here briefly...
First, be sure there's no confusion between '3rd harmonic',
which is a component of the drive signal at exactly three
times the fundamental, and the 3/4 wave resonance of a coil,
which is the first overtone resonance of the system, usually
between 2.2 and 2.8 times higher than the fundamental in a
typical unloaded coil.
Some situations that have been discussed in the past include:
a) A self-oscillating driver picks on the coil's first overtone
resonance and oscillates there instead of at the quarter wave
fundamental.
.................
I don't think any solid state coilers take (b) to be any great worry.
So far there is no evidence that any of this matters. Has anyone
deliberately tuned their coil's first overtone to the drive 3rd
harmonic, just to see what happens? All you need is just the right
amount of toploading. Does anything nice or horrible happen?
Do you get brighter streamers, or smoke, or just a slightly squarer
looking drive current?