Re: 3000 turn secondary

["Barton B. Anderson" <tesla123-at-pacbell-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Malcom, Marc, 

Tesla list wrote: 
>
> Original poster: "Malcolm Watts" <M.J.Watts-at-massey.ac.nz> 
>
> > > Original poster: "Metlicka Marc" <mystuffs-at-orwell-dot-net> 
> > > 
> > > Tesla list wrote: 
>
> <snip> 
> > I'm glad to hear you taking on this task. We should all discuss the 
> spacewound 
> > coil. There are several methods to spacewinding a coil. Personally, I 
> think you 
> > should spacewind the coil with the same number of turns keeping the 
> inductance 
> > as close as possible between coils. This will make the form a little
> taller, 
> > but... I don't know, what does anyone else think? I'll have to run some
> more 
> > numbers and look at the frequencies. I would like to see all the coils at
> the 
> > same resonant frequency. Sd should be the same between coils and proximity 
> > losses can then be quantified accurately. 
>
> If the secondary resonates at a different frequency it 
> necessitates some change in the primary, be it L or whatever. 
> Suddenly there are other variables changing. I agree Fsec 
> should remain the same. To spacewind with the same number of 
> turns, a smaller gauge of wire will be needed in addition to 
> what Marc already has. If on the other hand, Ns is reduced and 
> more top C is added to keep Fsec constant, top storage 
> suddenly changes. There are fish hooks in this exercise 
> everywhere. I've agonized over similar problems for months. 
> I once had two coils which were pretty much identical save for 
> the wire gauge. They were progressively stripped down as 
> several days of measurements took place. I should have fired 
> them up before reducing the from 5:1 to 0.5:1. A lost 
> opportunity. 
>
> Malcolm





Your right Malcolm, this is gnarly! If you keep the h/d aspect ratio the same
and increase the height and diameter appropriately, a near frequency match can
be made, but I had to use trial and error sizes until I came to a near match. 

For example, using an 8 x 38 secondary (29 awg): h/d = 4.75, Floaded = 28kHz, Q
= ~138. 

Now, same gauge with spacing the same as the wire size (.0121") at 12 x 57: 
h/d = 4.75, FLoaded = 29kHz, Q = ~111. 

Obvisouly, Q is not completely accurate, but the amount of change between the
two "might" be a nearmiss as for as the Skin depth. Anyway, you use the same
wire size, less wire with the added spacing. Slightly adjusting the primary
should get Q equal (Sd effect portion only). The proximity effect should be the
difference if everything else panned out (which it doesn't). 

The problem I see immediately is, even though the primary will need to change
very little as far as calculated tuning, the larger secondary will add toroid
shielding lowering the top capacitance. So in the real world, the primary tune
will actually be adjusted much more than the calculated value. Or can this be
done without a top load (remove the shielding problem)? 

I'm not sure of a good way to do this with or without the same wire size. 

Bart