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

[bartb]

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 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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