Re: Tuning an OLTC ... basics ...

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Dave,

At 07:17 AM 4/25/2005, you wrote:
> I have an old fashioned, spark gap Tesla Coil ...
>
> I wandered by WinTesla and the Java calculators. Here's the bare bones:
>
> 12,000 volts, 60 ma, which would like a cap of 0.0135 (13.5 nf) for Z match.
>
> Primary winding is what you'd expect, 10 turns, flat. The primary will go 
> "twanggg" at 240 Khz if I hang a 0.0241 mfd (24.1 nf) cap on it.
>
> Secondary is 12.5 inches of #25 wire, for 589 feet. 3.5" diameter.
> 1/4 wave length is 354 feet, which makes me wonder if they calculated it 
> right (grin).
> H/D aspect is 3.57 and likely number of turns is 643.
>
> The secondary would like to twang at 693.72 khz, except if I put a toroid 
> on it,
> which will bring it down to 240.40 khz, which will match the primary.
>
> A couple questions:
>
> How far do you generally have to move the primary "clip" to get an effect? 
> A quarter turn? An eighth?

It depends on many things.  Generally 1/4 turn but easily 1/8th if you are 
trying to get it just right.  Moving the wires to the primary coil also 
affects things a bit.

> I'm running with tinfoil on plastic now for caps and clearly don't have 
> enough capacitance. My 'scope shows a strong frequency being emitted 
> around 800 Khz, with all sorts of lovely harmonics. Is it getting time to 
> string up some MMC's? Or should I go beer bottles (grin)!

MMCs are definitely best there.  Beer bottle caps can be made to work but 
they are really only for the Zero expense systems.

> I do have a scope, can I use it to help me tune this puppy in? I do not 
> have a signal generator, alas, and although I hear rumours that there are 
> directions in how to build one from some 555 timers somewhere, I have not 
> yet found that!

It hides ;-))

http://www.hot-streamer.com/TeslaCoils/Misc/TCT/TCT.htm

> Do you think I should load this into my Jeep and drive up to Terry's and 
> shamelessly offer him a bribe?

There is a Tesla coil meeting every month in Denver at Bill's house.  I try 
to always go when the weather is good.  They are the second Sunday night 
from 5-10pm every month.  So that should be may 8th.  I will have my DRSSTC 
there and all.  Bring your coil to that and show it off and we can fix 
it.  I can also bring MMC caps if you need some.

Catch me off list and I will find the address and all.  There is also a 
local Tesla mailing list "GNATS" you should be on and Bill has his own for 
the many events he has at his house.

> Many thanks for helping this relative newbie,

There are getting to be a fair number of us now along the front range these 
days!!!

Any news from Red Rocks?  We could probably have a pretty good showing if 
that works out.

Cheers,

        Terry

>     Dave Small