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Re: Redesigning/tuning a coil

Original poster: "John Richardson" <jprich-at-up-dot-net> 

Hi Mike,

I think your 8x23 toroid will be fine.  Dr. R does this so that you know
about how many turns you will need before you make things permanent.  It
stinks making nice primary supports, etc, only to realize that your system
wants to be tuned a few more turns out.  Just scrape a bare spot every turn
out on the scrap wire and attach there.  This will let you know roughly how
many turns to make your permanent setup.

You can connect the ducting with tape, or cut a disc the same as the duct ID
out of 3/4 or similar plywood, and fit each end over this disc.  Retain with
epoxy or small screws.

Good luck,
John Richardson

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, April 17, 2004 10:34 AM
Subject: Re: Redesigning/tuning a coil

 > Original poster: pepperman-at-SoftHome-dot-net
 > Thanks for the suggestions--it sounds like using a sloped primary is
 > more complicated than I thought, so I think I'll go ahead with the flat
 > primary.  It sounds like it'll have plenty of coupling anyway.  I also
 > appreciate the ideas for the spark gap and short run times to keep
 > the caps cooler.
 > Dr. Resonance, I'm afraid I didn't understand what you were
 > recommending with testing the primary--you said:
 > "Also, a flat test "scrap wire" primary with 25-30 turns can be quickly
 > up with some slotted scrap
 > cardboard for a quick test of your entire tuning range.  Keep your
 > setting tight (under 0.100")and your variac below 30% until you find the
 > best pri resonant point."
 > How would using a temporary 25-30 turn primary help find the
 > resonance frequency for the final ~10 turn primary?  Were you
 > suggesting using normal insulated wire (e.g. 12-14 AWG) for the
 > test coil--and if so, how would you recommend varying the tapping?
 > I'm afraid I don't understand what you're suggesting here.
 > (To everyone): there's something else I'm curious about--how well
 > do you think the coil would run if it was tuned up to use the existing
 > 8" x 23" toroid, rather than replacing it?  I know there are more
 > ideal ratios (e.g. 5" x 20" or 6" x 26"), but how do you think the 8" x
 > 23" would perform?  Would it be too big for the 15/60 NST?
 > If it wouldn't do well, what other size would you suggest for one
 > made of corrugated aluminum ducting?  Also, a related question:
 > once you've curled the ducting around, what do you use to attach
 > the two ends?  I've read some comments about aluminum foil tape
 > disrupting the normal spark pattern, so I was hoping to avoid that...
 > Michael Johnson