Re: Pri./Sec. Tuning

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "James Robinson" <james.robinson@xxxxxxxxx>

Hi Mike,

>   My confusion is sometimes I see people say tune your primary lower or 
> higher. Shouldn't they ring at the same frequency?

I think I can at least answer part of the question - this is my 
interpretation of the world at least  - One reason for tuning the primary 
circuit to a slightly lower frequency than the secondary is due to effects 
of streamer propagation.  A streamer is not the product of only one spark 
gap "bang" and subsequent oscillation of primary and secondary, but of 
several, the ionized channel of air (that is the streamer) surviving from 
one bang to the next, growing each time.

As the streamer grows it effectively increases the capacitance of the 
top-load (toroid) to ground and hence lowers the resonant frequency of the 
secondary circuit.  So... to gain maximal streamer length it is optimal to 
tune the primary at a slightly lower frequency to compenstate for the 
"average" streamer loading.  Energy transfer does go on when not _exactly_ 
in tune, it is just reduced somewhat, depending on how far out.

Hope this is about right - comments???

>   Also as a tuning method, could you lightly couple a scope probe to the 
> circuit and drive the primary with a signal generator, then watch for 
> double peaks, then adjust the primary inductance (or capacitance) until 
> you have a single peak.

- that seems a perfectly good way of doing it.


>  "clear plastic"? How do I find out what type of plastic this is?
> It has a 1/4" wall thickness.

I don't know much about plastics - polycarbonate perhaps - if it appears 
indestructable, or if its acrylic (perspex) its probably broken already! 
Otherwise not a clue! - anyone else...

James Robinson

----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Tuesday, April 19, 2005 9:39 PM
Subject: Pri./Sec. Tuning


> Original poster: "Mike Knowlton" <amdx@xxxxxxxxxxx>
>
>   Hi all,
> I have been reading this group for about six weeks now and
> see confusing info on pri./sec. tuning. ( to me anyway)
>   My understanding is you have a secondary coil with toroid (tophat) that 
> is resonant at a fundumental frequency.
>   Then you wind a Primary, and wire it with capacitors in parallel, then 
> adjust a tap on the primary until the primary is resonant at the same 
> frequency as your secondary.
> (I understand this is performed with the secondary in place.)
>   My confusion is sometimes I see people say tune your primary lower or 
> higher. Shouldn't they ring at the same frequency?
>   Also as a tuning method, could you lightly couple a scope probe to the 
> circuit and drive the primary with a signal generator, then watch for 
> double peaks, then adjust the primary inductance (or capacitance) until 
> you have a single peak.
>                      Just curious,
>                                    Mike
>
> P.S. I aquired an 8.5" x 42" clear plastic tube today, I think it's my 
> start to building a TC !
>  "clear plastic"? How do I find out what type of plastic this is?
> It has a 1/4" wall thickness.