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Re: [TCML] Terry Filter for OBIT's

I finally got in my "OBIT" and it isn't an OBIT at all. It also isn't 9000 volts and 50mA. It is actually a power transformer built similar to a large MOT and is 6000 volts and 50mA. I'm pretty sure the 9000 volts was a typo. The guy I bought it from just would deliberately give the wrong information. It is also a very hefty, 21 lbs. The core measures about 4" by 4.5" by 6" and it is apparently wound with the primary underneath the secondary, as there are two wires that go from the primary binding posts to the center of the windings and the secondary binding posts are mounted on top of the windings. It is NOT wound like most MOT's I've seen with the primary and secondary windings separate. The secondary is also center tapped.
Since I now have very little to go by about how substantial this transformer is, I think it may be wise to simply go ahead and use a filter but since I only paid $20 for it, I'm having difficulty justifying the expense to do so. Maybe I should just use a safety gap?
While I'm at this, I have another question about this transformer. It does not have any shunts or even any room where there could be any shunts. So I don't know if this transformer is current limited in any way. My question is how do I determine if it is current limited?
I was thinking of using my 20 amp variac and power it at a low voltage. With a 120 volt primary and 6000 volt secondary the transformer ratio is1:50. So, I should be able to input 5 volts into the primary and have a relatively safe 250 volts out on the secondary on which I can place ever increasing loads to see if it stabilizes at some point. I can put my ammeter on the secondary leads and measure the amps as I change to lower ohm loads. If I do this, will the data extrapolate to the full 6000 volts? I mean is this a linear function? I'm fairly certain it is but I just want a second opinion. 
Thanks.
Paul
Think Positive
----- Original Message ----- From: "Jim Mora" <wavetuner@xxxxxxxxx> 
To: "'Tesla Coil Mailing List'" <tesla@xxxxxxxxxx>
Sent: Thursday, December 24, 2009 5:30 AM
Subject: RE: [TCML] Terry Filter



Hi Dex,

What is your reasoning in favor of NST's verses OBITS of equal
power/voltage. I will soon discover if this is true as I am building a obit 5000kv/23ma (1/2) the transformer. They are center tapped to ground and case and current shunted I believe. They are potted in asphalt generally. It may 
be interesting to un-pot one as the case in sealed when inverted.

Best,
Jim Mora
I'll post a picture when its done.
Happy Holidays everyone!
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Dex Dexter
Sent: Monday, December 21, 2009 12:13 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Terry Filter

They don't ,but I wouldn't use OBIT in tesla coil
service.NSTs are better.

Dex

--- pbbrodie@xxxxxxxxxxxxx wrote:

From: "Paul Brodie" <pbbrodie@xxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Subject: Re: [TCML] Terry Filter
Date: Mon, 21 Dec 2009 12:44:30 -0500

I recently purchased a 9kV 50mA OBIT or at least the seller says it is an
OBIT. This appears a little bit hefty for the purpose. Anyway, do these
transformers require the same sorts of protection that are used with neon
sign transformers?
Paul
Think Positive
----- Original Message ----- From: Dex Dexter 
 To: Tesla Coil Mailing List
 Sent: Monday, December 21, 2009 05:23
 Subject: RE: [TCML] Terry Filter


 I run my static gap coil without any filter at all.
 NST is 5kv/20ma ,and safety gap is set for
 the breakdown voltage of aprox 10 kV peak.
 I've   never saw it arcing so the breakdown
 voltage of my static gap is probably below 9 kV.
 Position and way of connecting the gaps with respect to
 NST is important.Both gaps should be paralleled with NST.

 Dex

 --- Gary.Lau@xxxxxx wrote:

 From: "Lau, Gary" <Gary.Lau@xxxxxx>
 To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
 Subject: RE: [TCML] Terry Filter
 Date: Mon, 21 Dec 2009 02:16:43 +0000

 If you build a filter with MOV's targeting a 15kV NST, and you use a 9kV
NST, the MOV's will allow a peak voltage of something like 22-23kV before
they kick in. With a 9kV NST, the maximum voltage that *should* be allowed 
is 9000 x 1.414 = 12726, call it 13-14kV.  So it would be permitting
too-high voltages that should have been clamped.  One needs to select the
correct number of MOV's for the NST voltage used, for the same reason that
one needs to set the safety gap for each situation.

 Regards, Gary Lau
 MA, USA

 > -----Original Message-----
 > From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
 > Behalf Of chipford@xxxxxxxxxxxxxx
 > Sent: Sunday, December 20, 2009 8:31 PM
 > To: tesla@xxxxxxxxxx
 > Subject: [TCML] Terry Filter
 >
> I have my terry filter about 50% done. While building it, I asked myself 
a question.
 > Why would a person build anything but a Terry Filter capable of
protecting a NST of
 > 15,000 volts? I ordered 14 MOV's from dig-key. For 4 or 5 dollars more,
I could
 > have had 16. Now if i want enough for a 15k trany, I gotta pay shipping
 > again.Correct me if I am wrong. If I build a Terry filter capable of
protecting a 15K
 > volt trany, I can use it to protect my 9000 volt NST without any
modifications. I bring
> this up because, as we all know, parts get swapped from coil to coil and 
if I decide
> to built a larger coil with my 15k trany later on, I could've just moved 
it over without
 > worry. Am I wrong?

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