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Re: [TCML] How necessary is a Terry Filter



Hi Ed and David,

I've experienced an NST failure using both a safety gap and a Terry filter (different times)! First failure was without a Terry Filter. Second and 3rd failure was with. Their not 100% full proof. I do run a variac for that extra 14% output voltage. I still use the same NST for this coil. I did depot, it was messy, it was successful, and it's now a powerful little NST. The first depot was terrible. But using wax (wanted the hardened wax to hold tranny and wiring in place), depotting is now a piece of cake.

I've also carbon tracked a Terry filter once (components poorly laid out). It's in a new box now and so far so good. It's got a lot of run time on it since and some very long runs at that. I believe that my NST failures were due to running in resonant charging mode. I run a little closer to resonance than the standard to take advantage of resonant charging, and with that, the transformer gets a little boost. The last failure I had, the Terry filter went ballistic. I checked all the components after and they seem to be fine. But it was a good indication to stop running the coil. Now that I've lowered k a little, it can run non-stopped. And I mean that. It's the first coil that I could walk away from and come back 1/2 and hour later and I'm sure it would still be running (not that I would ever do something that stupid).

There is something else helpful with my particular NST (originally 12/60). During my first depotting, besides pulling out 1/2 the shunts for a big current boost, I also removed several layers of secondary windings so that the tranny is now 10.6kV. This gives me some breathing room. There are a lot of things we can do with our NST's to make them perform, but it's just a matter of how much work you want to put into them.

BTW, I really like Franceformers! Probably one of the best NST's out there. I enjoy simply flipping my 120V switch and watching it go. It's a good working coil that I can fire up within a minute (and my son often brings his friends over and begs dad to run the coil for them). I enjoy that a lot! Quick, simple, and a good performing NST coil! I've always used piggy power before that. I nice little coil does have it's advantages.

Take care,
Bart

David Rieben wrote:
Hi Ed, all,

That is a good question and I think it may be just a matter
of a "too much protection is better than not enough" men-
tality. I know from personal experience in the past that I
have let the smoke out of numerous NSTs. Of course I
was indeed guilty of opening up the main gap to get ever
longer sparks and usually did not even have a safety gap
in my design. In the beginning I just didn't know any bet-
ter and the only "protection" that I would have at all was
the proverbial RF choke coil. Now we know that an RF
choke coil may even worsen the kickback situation. How-
ever, it seems from personal experience that even as I did
begin to employ more of the currently accepted means of
protection, that I would still sometimes fry one here and
there. Now I cannot give any personal review on the Ter-
ry filter as I never did get a chance to employ one of these
into any of my coils. That's because that by the time that I
had become privy to the Terry filter, I had already aban-
doned the NST as a power transformer approach and had
already graduated to the PT and "piggy" club ;^) And of
course once I got a taste of the raw power from the pole
pig route and the fact that pole pigs or PTs do NOT burn
out, I had no interest on retrograding in the power and
the reliability departments. Even to this day, I still despise
NSTs for the "bad memories" that they have left me with.
As a matter of fact, I have recently hatched the idea of
actually building a smaller coil than my current Green
Monster coil: http://www.teslauniverse.com/members/drieben/
One that is still fairly large but yet small enough to plug into
a standard 120 volt, 20 amp circuit and keep inside of my
garage when I fire it. And I am not even considering going
the NST(s) route for the power transformer but am plan-
ning on using a properly ballasted 120:1 PT for this purpose.

O yea, I've tried the depotting thing too, to resurrect a dead
NST. What a mess! I wouldn't go through that much trouble
to resurrect an inherently fragile transformer ever again! And
no, the re(de)pot attempt was not successful for me, either.
I just ended up with a black, tarry mess that was still a defunct
NST and made great trash can fodder!

What amazes me now is how many coilers that have claimed that
they have never burnt out an NST in the past, even without the
proper filtering. All that I can say is that they must have gotten
their NSTs from a different source than I got mine from! To me,
NSTs seem unduely fragile for our use and use as a power
source for a Tesla coil is certainly outside of their intended design
parameter. However, they are still indeed very popular for this pur-
pose to this day, as nearly any successful attempt to obtain a decent
one off of ebay will attest to your pocket book! As a matter of
fact, I have just recently obtained a new 120:1 (14.4 kV) indoor
use type, double bushing PT (85 lbs), with 3 fuses, off of ebay and
I have less total $ in this purchase than I would if I had purchased
a 60 mA, 12 or 15 kV NST going throught the same ebay route!
BTW, the PT retails for $1,951.03! I just won it on Dec. 26 and
am still awaiting its arrival.

Sorry for the soap box rant but as you all can probably see, I
have really been touched by the numerous NST failures that I
have esperienced in the past - failures that set me back a whole
lot of $$$ that I really didn't have to spend at the time.

What can I say?
Pole pigs and PTs rock ;^)

David Rieben






----- Original Message ----- From: "Ed Phillips" <evp@xxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Sunday, December 30, 2007 3:18 PM
Subject: Re: [TCML] How necessary is a Terry Filter


Hi  Guys

In building a new coil I am wanting to do it right and also hope to have it around for a long time. When I built my first coil I had no transformer protection other than a simple safety gap. Both of my transformers are still good even with out the filter. I was wondering if I really need this layer of protection? I run my coil with two 12/30 NST's and an RQ spark gap that contains 6 segments of 1in. copper couplers. Second part I am wondering about AC line protection? I see that some use an RF filter on the AC input. If anyone has any advice /parts list or completed Terry Filter I would also be interested in cost. I'm trying to work within a pretty tight budget at the moment so I would suppose that making the filter myself would be best but just thought I would ask.

As always thank you for your time and  guidance,

Vinnie"

I'd like to add a slightly different question. What additional protection does the filter add if the transformer is equipped with suitably-adjusted safety gaps? Has anyone ever experienced an NST failure when it was so equipped?

Ed

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