Re: Tuning Question

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Dennis,

At 06:30 PM 11/20/2006, you wrote:
> I've read plenty about the importance of tuning coils at low power 
> (variac & gap width) to avoid damaging components until resonance is 
> achieved.  I also recall a post discussing, once a coil is tuned at 
> low power, you need to further tune the coil at full power due to 
> additional secondary capacitance created by the streamer itself.  I 
> have some questions about this.
> Is additional capacitance of a full power streamer significant 
> enough to warrant the additional tuning excersize?

"Barely" it depends on the coil, but it is about +5% added to the top 
capacitance.  Problem is, just "moving" the primary "wires" is just 
as significant.  In general, tuning the primary frequency 5% low is 
fine. However, it might not make much "real" difference at 
all.  Solid state coils with there deadly reproducibility and guys 
with crystal control frequency counters and such can "detect" the 
difference, but nobody else can ;-))

> If so, I would assume you are looking to increase primary inductance 
> to compensate for increased secondary capacitance - so you'd be 
> tuning outward (increasing primary turns) - correct?

Yes, the primary should be tuned a little lower in frequency from the 
secondary.

> I tried this & seemed to find increased performance tapping the 
> primary at an additional 3/4 turn - i.e., from 13 7/8 turns to 14 
> 5/8 turns on my 15/60-0.015uF system.  Seems like a lot of 
> additional primary for the small increase in secondary 
> capacitance.  Does this seem to be in the ballpark for full power tuning point?

Whatever give best performance is fine.  The problem is when you 
moved the tap point you also moved "the wires" going to those 
points.  Those wires are just as significant in varying the 
inductance.  No hard rules there, but to just "fish around" for the 
best sparks.  Recently I have tried to keep the wires going "down" at 
a "90 degree angle" which removes them from significance.  That works good.

> My NST died a few days after reaching this higher performance 
> level.  I'm wondering if I killed it with improper tuning.

I doubt it.  The firing tuning should not kill an NST no matter 
what.  Your cap is the LTR value too with a fixed gap...  Sometimes 
old NSTs "just die"...  But aside from old age, I can't see anything 
that should have hurt it.  what when wrong with it?  Shorted 
side?  Maybe just the old tar arced through...

You gap should "short across" the NST too.  See the conclusion at the 
bottom of the page here:

http://hot-streamer.com/TeslaCoils/MyPapers/primarycircuits/pricir.html

RF stress on the windings will kill about 5% to 10% of NSTs given time...

> I want to optimize performance, but would also like to avoid killing 
> another transformer.
> Any tips or suggestions on doing this additional full power tuning 
> excersize.  I'm concerned I'm missing something here.

There is always the "Terry filter".

http://hot-streamer.com/TeslaCoils/Misc/NSTFilt.jpg

It seems to make killing NST super hard to do...  But in general, you 
seem to be doing things "right".

Cheers,

        Terry


> Thank you - Dennis Hopkinton MA