RE: Primary coil form

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Vanderputten, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <gvp-at-pvaintl-dot-com>

For smaller coils, what is the performance difference between a
helical/tubular versus the 'inverted cone" primary?  
My past coils (40 years ago) were all helical and performance was mediocre
compared to what I see today. However, given my modest requirements and the
difficulty in creating and inverted cone, what do I give up with a helical
primary?
Is flat better than Helical?

Specs = 
3.5 x 15" secondary, 900+ turns of #28 dbl 
12/30 nst
Fritz/Lau protection circuit
.0066 mf /30 kv cap

Thanks

Gary