Re: [TCML] Terry filter alternative

[sparktron01@xxxxxxxxxxx]

Hi DC, List

I am presently using a modified Terry Filter, where the R is a 50W, 3K ohm
wirewound resistor on each "knob" of the NST (9kv, 30mA), with Safety SG
and 2x2500pf doorknob capcitors tor ground.  The resistors do get quite
warm (must be doing their job  ;^D ).  OBTW, 3k ohm X 0.03A is 90V drop
per side (~ 2% V total drop).  To protect the transformer, a good deal.
No evidence of flashover or HV degradation of resistors either.

I have also used air core LC low pass fitler on small PT and "Radar/Laser"
(80:1 to 100:1) non-shunted transformers and haven't experienced a
failure on those systems (KOW).

Regards
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA. USA

 -------------- Original message ----------------------
From: resonance@xxxxxxxxxxxx
> 
> 
> 
> 
> With pole and PT xmfrs you may consider just using a 4" dia x 18 long PVC
> tube wound with #26 AWG PVC covered wire.  This clips all the really VHF
> and other nasty transients and keep most of the most dangerous transients
> out of the PT or PPs sec coil.
> 
> I use this on all of our PT and PP powered systems.  Sometimes we throw in
> a resistive network as well, usually approx 12 --- 200 watt, 500 Ohm
> resistors connected in parallel between the input RF choke and the HV xmfr
> bushing.
> 
> Dr. Resonance
> 
> 
> > 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.
> 
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