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

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 ;-))


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.



Dave Small