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Re: terry filter theory



Original poster: "resonance" <resonance@xxxxxxxxxxxx>



The caps serve as a rapid ground source for the high freq transient currents due to their very low high freq reactance. The resistors destroy the circuit Q factor and reduce the transients. The varisters serve as a direct overpotential safety value to allow excessively high resonant potentials a direct path to ground. The safety gap serves as a final safety valve but these are not usually required as the varisters serve the same purpose ---
provide a quick, safe path to ground.

I usually split the resistors into two 500 Ohm, 50 Watt resistors, one on each side of the series caps to ground. From the tank circuit the oscillation first hits a resistor, then the series caps to ground (low reactance), then another 500 Ohm, 50 Watt resistor, then the varisters to ground, and finally a safety gap to ground. This will stop almost anything that could damage your nst. Be sure to use one of these systems off each xmfr bushing. The power reduction is so slight it does not adversly effect the TC output spark length.

Terry's original circuit used a 100 Watt, 1,000 Ohm resistor.

Some transformers can develop a ferro-resonance with a tank capacitor and this type of filter prevents this ferro-resonance while simultaneously destroying any reflected oscillatory currents from the tank circuit, e.g., the pri cap and pri inductor.

Dr. Resonance



parts for this filter I would like to grasp the theory behind the design of your filter. Do the capacitors store excess current that would otherwise damage the nst? Are the movs' there to protect the nst from surges? Will the 1k ohm resistors reduce the input voltage? Does it take an arc at the safety gap to operate the terry filter in the first place? Is it overkill to add more components? Will extra components reduce the spark length?