SV: NST resonance - Terry's testing

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

Original poster: "Jan Ohlsson by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jan.ohlsson-at-mbox319.swipnet.se>

Thank you for probing my results, Terry!

As your results came so close to the theoretical value I think we have to
assume that yours are correct. I must have made a serious measuring error
or my transformers are weird, or both. 

Perhaps my NST:s contain power factor correcting condensors, as was
suggested on the list. I will try to get manufacturers data for them. I
have thought a bit about my makeshift voltage divider network, used instead
of a regular HV-probe on the secondary side. Perhaps I went over the top
with the resistor values and invited all sorts of non wanted signals to
sneak in by capacitive coupling.

I will try to review my measurements later this week, but for now I think
we should look upon Terry´s as the correct ones. It really is very
satisfying if measurements coincide with the theoretical models, as Terry´s do!

Best wishes
Jan

----- Original Message ----- 
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, February 11, 2001 9:48 PM
Subject: Re: NST resonance - Terry's testing


> 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 don´t 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
> >
> >
> >
> >
> >
> 
>