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LTR caps and thin wire secondaries, etc.
It is even more important to use thin secondary wire if you're using
an LTR sized cap. This is because the LTR cap will use fewer primary
turns (compared to a reso-cap). The LTR cap is good of course because
it keeps the voltage lower on the cap and the NST. Fewer primary turns
gives a lower surge impedance and greater gap losses.
Of course a coil that uses thicker wire and fewer turns will work
fine, but may see a 10% spark length penalty.
It is also more important to use thin secondary wire if you're running
at a low bps, because low bps requires the use of a larger cap. I've
seen the best overall "efficiencies" at low breakrates (around 120 bps).
However, any coil; high bps or low, LTR or reso, can benefit from
using a thinner than normal wire. The 28awg wire I use on my small
coil is suitable only for low power work. As a coil become physically
larger with a larger power input, the secondary wire size should be
increased proportionally. I have never tested these ideas in a large
coil but it should work based on the theories.
Contrary to what I've stated previously, I now believe that a wider
secondary may give an advantage. By using a wider secondary
(6.5" vs. 4.2" for example), one can use the same number of turns,
(1600 for instance), but achieve even greater inductances in both
the primary and secondary.... thereby driving the primary surge
impedance even higher.... and thereby reducing the gap losses
even more, and making the spark output even longer.
I was concerned before that the wider secondary would lower the
output voltage too much due to the larger Cself, but I now suspect
that the benefits of the higher primary surge impedance outweighs
the large Cself issue. There is also a viewpoint that I've heard....
that a large Cself is a benefit, but I don't know for sure.
Let me say again, that for anyone who insists on using thick wire,
they can still obtain excellent performance simply by increasing
the input voltage, although it is likely that they will obtain even
better performance by using both a super high input voltage,
along with a thin wire (high inductance) secondary. The high
inductance is a key since it leads indirectly to lower gap losses,
and longer spark outputs. Higher input voltages also result
in lower gap losses.
Again, by *thin*, I don't mean 28awg on a huge TC. A huge TC
will require thicker wire than that. There has to be a sense of
proportion. I just mean thinner than what is commonly used,
(and more turns which is the key).
I'm working on a new TC setup which will use ~46kVpeak on
the primary. This should give even better results.