Re: NST resonance - Terry's testing

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Jan,

I hooked up my toys and tried your resonance experiment.  The equipment I
used is a follows:

Agilent 33120a signal generator
Tek TDS210 scope
Tek 5100 HV probe
ACTown 9000V 30mA NST (new)
Low-Z Wide band amplifier
MMC array set to 8.37nF

The first frequency sweep is from 10Hz - 110Hz (linear scale) with a 5
second sweep time.  The input voltage was 1.00Vrms.  The response is shown at:

http://hot-streamer-dot-com/temp/J10-110.jpg

The second test was with a sweep from 10Hz to 1010Hz:

http://hot-streamer-dot-com/temp/J10-110.jpg

It appears there is only one resonant peak in these ranges at about 62 Hz.
The voltage amplification is about 400X!  At full input voltage, that would
give a "theoretical output voltage of 48000 Volts (that's why we have
safety gaps!!)

The theoretical resonant cap size for a 9/30 NST is 8.842nF but I could
only get 8.37nF.  that should give a resonant frequency of 60 x
SQRT(8.842/8.83) = 61.67 Hz.  That number agrees nicely with the J10-110 graph.

A picture of the "laboratory :-))" setup is at:

http://hot-streamer-dot-com/temp/P2110020.JPG

People always like to see pictures...

So, it would appear that my test shows all is well with the present method
of finding resonant cap values.  I wonder if your setup needs one of those
nice amplifiers to drive the NST.  The output resistance for the amplifier
will be directly reflected back into the circuit which may cause odd
effects.  Also be careful with the voltages.  With only one volt input, I
can get over 400 volts on the output of the NST!!

Thanks for suggesting this neat experiment!!  In my case, it worked great
and appears to verify the NST/cap resonant methods. 

Cheers,

	Terry


At 08:06 PM 2/8/2001 +0100, you wrote:
>I am a newcomer to the list, so please forgive me if this is covered before! 
>
>To investigate the resonance of a 8/60 NST I parallelled the secondary with 
>MMC:s from 1.6 nF to 6.8 nF and made impedance sweeps with an audio sweep 
>generator of the primary impedance. The impedance curve of the primary 
>showed as expected a sharp impedance peak of high value and then a gentle 
>rising caracteristic towards the upper end of the audio spectrum. The last 
>probably due to high frequency losses in the NST core. 
>
>What surprised me was that the center frequency of the resonance peak did 
>not change as expected if I, for example, quadrupled the value of the MMC. 
>That should theoretically give half  the resonance frequency, but the actual 
>value was higher than that.
>
>I can only come to the conclusion that there are other sources of 
>capacitance at work, probably within the NST, of the order of a couple of 
>nanofarads. That would make simple calculations of NST/MMC resonances 
>unpredictable.
>
>I also made some sine sweeps with a constant current source to the primary 
>and registered the secondary voltage through a very high impedance voltage 
>divider, the MMC still in parallell. What took me by total surprise was that 
>the curves showed several resonances without a simple arithmetic connection. 
>The lower part of the audio spectrum was more or less filled with resonances 
>of different magnitudes. To be able to exclude instabilities in the audio 
>amplifier that was used to feed the NST primary I tired the same thing with 
>the audio generators 300 ohms output directly to the primary, but that gave 
>me the same kind of curves. I also changed the NST to a 4/45 and tried 
>different values of the MMC, but the resonances just moved a bit, the 
>general character of the frequency response was the same with multiple 
>resonances. These resonances donīt seem to couple to the primary, as there 
>is just one resonance evidenced by the primary resonance sweep.
>
>Have others on the list made similar tests with a sweep generator on NST:s 
>and caps? My result seems to point out that the NST do not behave as the 
>lumped component models commonly used for transformers suggest. If that is 
>the case many values of primary caps could give a resonant condition with a 
>specific NST. One more argument for a good RCR filter between NST and 
>primary, in that case.
>
>Please feel free to critisize my methods and conclusions, I am after all a 
>newcomer to coiling. And to those of you who wonder: Yes, I have fried a NST 
>before I started thinking and set up the sweep generator!
>
>BTW, are there other coilers in my homeland Sweden?
>
>Jan
>
>
>
>
>