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

[DC Cox]

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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