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"Slinky" Primary / Sloped Archimedes Spiral Primary Equation


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From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Sunday, August 23, 1998 11:31 PM
To:  Tesla List
Subject:  Re: "Slinky" Primary / Sloped Archimedes Spiral Primary   Equation

Tesla List wrote:
> 
> ----------
> From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
> Sent:  Wednesday, August 19, 1998 12:26 PM
> To:  Tesla List
> Subject:  Re: "Slinky" Primary / Sloped Archimedes Spiral Primary   Equation
> 
>   Bert -
> 
>   Thank you for replying to my post. However, it appears that I was not
> specific enough with details and you misunderstood my questions. It is true
> that changing other TC parameters will certainly change the TC output.
> 
>   What I had in mind and referring to your diagram and equations was only
> changing one variable and that was the angle "X". For example, if a coiler
> had a choice of using a flat spiral or a cone type with R = 3, Z = 5, and
> N= 10 turns which should he use to get the best output? The secondary would
> be a typical H/D ratio of about 3 or 4. The angle could be anything from
> zero to 45 degrees which would require the usual tweaking.
> 
>   As I mentioned in my post the cone inductances (Lp) vary only slightly
> with angles from zero to about 45 degrees. In fact the differences in this
> case are less than 2 uh of the flat spiral inductance. This is less than
> the normal wiring connection inductances. With secondary inductance (Ls)
> constant the Ls/Lp ratio effect would be very small and within the error of
> actual tests.
> 
>   The bottom line is I do not believe it is worth the extra work of
> building the cone type primary because the advantages, if any, are
> negligible. Do you know of any equations or actual tests that would prove
> otherwise?
> 
>   John Couture

John and all,

Sorry for the delay in responding - I just got back into town. 

While it is true that the primary inductance doesn't change dramatically
as you increase the angle from 0 to 45 degrees, the mutual inductance
between the primary and secondary will increase significantly (50-75%),
all other things being the same. 

Now, if a given system is empirically determined to run optimally at a k
of say 0.18 due to insulation withstand and gap quenching
considerations, a primary coil constructed in ANY of the three
configurations, when wound with the same materials and having the
identical primary inductance will provide virtually identical
performance when adjusted to have the same k. However, since the pancake
coil may be the easiest to construct, while also providing maximum
toroid:primary distance, it's the winner in my coil-building book - I
agree with your conclusion.  

-- Bert --