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Re: Terry's Little SISG Research Coil

Original poster: "Dr. Resonance" <resonance@xxxxxxxxxx>


At 139 kV what is your spark length to a grounded rod? Interested in the kV/inch for this coil.

Dr. Resonance

Long long ago, in a time I forgot,... I started working on a "little research" Tesla coil... A very simple, reliable, repeatable, solid state thing... Big sparks were not the issue, but rather a coil always "ready to go" in any situation. No lost cables, damaged secondaries, blown parts...

Well, the SISG was made to run it, which was like a four month "delay" :o))) It's parameters are probably more accurate and better known than any coil on Earth ;-)) It's output is deliberately "limited" so scopes, test equipment, and computers can be near it.

A paper describing it is here:


Forgive if it is "technical"...  This is a VERY "technical" coil...

It runs rock solid and is totally repeatable, even if I go back and measure the parameters after long running. No other coil I have every had has been totally "repeatable"...

It is an "odd" thing... It runs at 120, 240, 360 , more... BPS depending on the variac setting (as designed ;-)) But the "gap is "silent" (Well, you can hear the magneto constriction if you try) and the running is "perfect". It does not sputter, hiss, or vary. It runs almost like a DRSSTC but no electronic "brains"... I actually seems far more "stable" than my DRSSTC... It is super cool for corona stuff!! Peak voltage is 139kV, and yes, it really IS that accurate!!! I suspect much of the seeming stability is due to it being pretty lower voltage.

It will not breakout without a "point". Cool for many tests... But if you were wanting a "real" coil, just add another MOT to double the voltage >:-))) Higher bridge PIV too... But "I" kept it tame with just one MOT so I would not blow it up like I have all my "other" research coils :O))

It is pretty "cheap"!! I just used SISG boards I had as scrap. Just very common stuff and four CD caps... I spent ~$75 on stuff for it mostly the Lexan, odd parts, and pretty woodwork ;-)) There is not a lot in there:

http://drsstc.com/~sisg/files/SISG-coil/P7150184.JPG    (big file)

I should note three things I found of note...

1. The secondary coil was not effected at all in any measurable way buy the massive MOT nearby.

2. The secondary has a "Q" of 213 and an AC resistance of 147.6 ohms which is vastly "better" than all the programs predict... I don't know why... I have measured that in several ways now and my measured numbers hold solid and the separate types of measurements agree to 5%. Maybe I just made it special good ;-))


3. The primary resistance is 0.155 ohms. 0.06 ohms of that is the SISG. I used 12 gage stranded wire for the hookups in very short lengths and big brass for the connections... But there is 0.095 ohms in the primary coil and wiring. Not a big deal, but "significant"... The SISG stuff places new demands on primary resistance. A conventional spark gap at 3 ohms would render the primary's "Q" at about "1" so it would not even run :o))))


Losses are:

Coil Power 53.1 watts
SISG 9.55 watts
Primary Loop R 15.12 watts
Secondary Rac 2.4 watts
Arc 25.9 watts

If I could quench on the first notch (11.2uS), this changes to:

Coil Power 53.1 watts
SISG 6.89 watts
Primary Loop R 10.9 watts
Secondary Rac 2.88 watts
Arc 30.8 watts

I looked into quenching by careful selection of R4 on the SISG. However, the voltage drop at the gate and the currents required per time did not add up. The e^-t/RC curve does not have the drive at the right times to quench but still sustain the "good" currents. At higher currents, a low R4 (like 60 ohms) just will not work for fast quenching :-( It will take more "electronics"...

So that is what I have been doing this last six(!!) months...