[TCML] Terry filter - does one need the current limiting resistors with a current limited NST?

[DC Cox]

Unfortunately, it's not this simple.

Harmonics, reflected harmonics, and the standing waves they create all have
to be considered.  Part science, part art, like blasting.

Dr. Resonance




On Sun, Apr 6, 2008 at 7:24 PM, DC Cox <resonance at wildblue.net> wrote:

> It does spoil the Q factor of the circuit loop between the xmfr and
> sparkgap.  Should this be low impedance the Q factor may multiply the
> xmfrs
> potential in this loop.  Most any R-C filter with the resistance will
> lower
> a Q or quality factor.
>
> Any additional resistance in any circuit always reduces the Q factor,
> hence
> the name "Q spoiler".  You are right --- it does not spoil the Q factor of
> the tank (LC) circuit which we wish to maintain as high as possible.
>
> Dr. Resonance
>
>
>
>
>
> On Sun, Apr 6, 2008 at 6:52 PM, Lau, Gary <Gary.Lau at hp.com> wrote:
>
> > No DC, the resistors in a Terry filter have nothing to do with spoiling
> Q.
> >  The resistors serve only as the R in an R-C low pass filter.  Back when
> > folks were blissfully using chokes in protection circuits, there was
> well
> > founded concern that the chokes would resonate with the bypass caps in a
> > harmful way (which they would!), and it was thought that adding series
> > resistance to the chokes "might" reduce that hazard.  In a qualitative
> sense
> > it seemed reasonable, but with the availability of circuit simulators
> and
> > inquiring minds, it became clear that there would be significant
> resonance
> > with a choke unless the de-Qing resistor was so high that losses would
> be
> > unacceptable.  And if there is no choke, there is nothing to De-Q.
> >
> > That chokes serve no useful purpose in protection circuits has been
> > thoroughly and repeatedly discussed here, so it surprises me that you
> would
> > suggest using them.  What analysis leads you to that opinion?
> >
> > Regards, Gary Lau
> > MA, USA
> >
> > > -----Original Message-----
> > > From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com] On
> > > Behalf Of DC Cox
> > > Sent: Sunday, April 06, 2008 4:39 PM
> > > To: Tesla Coil Mailing List
> > > Subject: Re: [TCML] Terry filter - does one need the current limiting
> > resistors with a
> > > current limited NST?
> > >
> > > The function of the resistors in a Terry filter is NOT to limit
> current.
> > > Their main function is to spoil the Q factor of the circuit thus
> > preventing
> > > harsh high current spikes from reflecting back towards the nst
> > transformer.
> > > You still need them.  I divide mine into two on each leg ---- one just
> > > before the caps to ground and one just after the caps to ground.  I
> use
> > 300
> > > Ohm 25 Watt resistors --- four of them.  Also a small RF choke.
>  Contact
> > me
> > > off-list if you want my schematic.
> > >
> > > Dr. Resonance
> > _______________________________________________
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> > Tesla at www.pupman.com
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> >
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