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Re: NST resonance - Terry's testing
Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-uswest-dot-net>" <tesla123-at-pacbell-dot-net>
Hi All, Terry,
Great job Terry! Jeeeeze, I wish I had your toys (but not your credit card
The J10-1010.jpg link was incorrect. Here's the corrected link.
Tesla list wrote:
> 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
> The second test was with a sweep from 10Hz to 1010Hz:
> 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
> A picture of the "laboratory :-))" setup is at:
> 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.
> 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
> >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?