-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of Dave Goodfellow
Sent: Monday, December 31, 2007 10:25 AM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Terry filters
I have bought into the idea that chokes are not the answer for protecting
nst's based on the evidence that you (Gary) and others on the list have
produced. I don't agree, however, with your claim that a series inductor
does nothing to from a low pass filter. In my old car stereo days, I used
chokes on woofers to keep the high frequencies out of the speaker.
Admittedly, when I listened to the woofer with and without a choke, a
choke
alone didn't just drop the high frequency right out of the sound that the
speaker was fed. According to my old Fosgate manuals, a choke on it's own
would attenuate the signal at 6 db per octave. The bigger the choke, the
lower the frequency the attenuation would begin. This means that if the
speaker were 8 ohms, and your choke was stated to be 100hz for a 8 ohm
woofer, it simply meant that it would present more than 8 ohms to the
amplifier at 100 hz and up, and increase the impedance by 2x's (I think)
with each doubling of frequency. If you wanted 12db per octave, a
capacitor
of a specific value would be placed on the downstream side of the choke,
to
the negative feed of the speaker. If one wanted 18db per octave, a second
choke would be placed in series, down stream of the first choke.
When I thought that chokes were necessary for Tesla coil building, a
ferrite
core car stereo woofer choke was exactly what I used on the high voltage
side of the transformer! Naturally, to find a capacitor so large and of
sufficient voltage to use the car stereo formula was impractical, so I
just
used the choke mounted directly on the hv bushing.
Your chokes looked like a good design and your testing is convincing
that chokes are not helpful. Unwanted capacitance I believe is the culprit
in making chokes bad. I have found the effects of unwanted capacitance
working in A/V. As our video signals are becoming higher and higher,
cables
have to become shorter. That tiny bit of capacitance in coax can kill the
signal when the cables are too long!
Dave Goodfellow
----- Original Message -----
From: "Lau, Gary" <Gary.Lau@xxxxxx>
To: "'Tesla Coil Mailing List'" <tesla@xxxxxxxxxx>
Sent: Monday, December 31, 2007 12:51 AM
Subject: RE: [TCML] Terry filters
I'm sorry Dr, but anecdotal evidence like this is going to set us back to
using leeches and bloodletting.
No one has ever performed a study on failure rates, ON EQUIVALENT
HARDWARE,
comparing R-C filters and L or L-R filter networks. But there is
overwhelming theoretical and simulation-based evidence that show that R-C
filters are the superior topology.
Adding just a series inductor with or without a series resistor does
nothing
to form a low pass filter. You need a capacitor; this is elementary
circuit
analysis. On what basis do you conclude that this would "catch especially
the very nasty high freq transients "?
I maintain that the use of chokes in NST/PT/pig protection networks should
be abandoned.
Regards, Gary Lau
MA, USA
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of resonance@xxxxxxxxxxxx
> Sent: Sunday, December 30, 2007 9:21 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Terry filters
>
> If you are really on a tight budget using used NSTs and can't afford a
> full Terry filter, there is an alternative.
>
> For almost 20 years I used a simple pair of air core RF choke made of 2"
> ID x 12 inch long PVC tube. I wound it for 10 inches with #26 AWG PVC
> covered wire. It seemed to catch especially the very nasty high freq
> transients that could break down the NSTs HV coils as these transients
> can
> form a "spider-web" like effect, essentially "crawling" over the
> windings
> until they connect and then the main power flows causes failure.
>
> Using a pair of these simple air core chokes I had only one failure in
> nearly 30 years. Some of these coils with NSTs and these simple chokes
> are still in daily operation at museums for over 15 years.
>
> The failure I had was also a used NST so that could have entered into
> the
> factor --- the xmfr might have been ready for a failure from prior neon
> service.
>
> Food for thought anyway.
>
> Dr. Resonance
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