RE: [TCML] Terry filter - does one need the current limiting resistorswith a current limited NST?

["miles waldron" <mileswaldron@xxxxxxxxxxx>]

So, do the R's in the terry filter along with the caps, make a low pass
filter? If this is true, then it should be easy to figure out what the cut
off noch is, or make a bode plot.

Miles Waldron
678-557-7737



-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of bartb
Sent: Sunday, April 06, 2008 11:03 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Terry filter - does one need the current limiting
resistorswith a current limited NST?


Huh? In what way did DC mention using chokes?

I think all DC said is that the resistors would spoil Q as their main 
function. Granted, I don't agree with that, but he's not suggesting 
using chokes. I think this is just a misunderstanding of the resistor 
function. The "designed" function of these resistors is to dump 
transients that would otherwise find their way back to the NST hv 
windings, and in a damaging way. Some Q affects if the cap were resonant 
or maybe ferro-resonance might be affected (not sure about that), but 
this is not the main function of the resistors.

Bart

Lau, Gary 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@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] 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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