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Re: Terry Filters - Basic Education



Original poster: "resonance" <resonance@xxxxxxxxxxxx>



The main function of a "Terry filter" is to block any RF currents from getting back into the high voltage winding of the NST. Terry filters do this in several ways:

First, the resistance effectively spoils the "Q" factor of the circuit which kills the large transient spikes.

The small capacitors allow any remaining RF currents to go directly to ground where they are neutralized.

The third defense is a string series of varisters. Varisters are variable resistors that can either block a voltage, or, then suddenly change into good conduction (low resistance) once a certain peak voltage is reached. In this way the over-voltage is shorted to ground as the resistance drops to a low value.

The final defense is a safety spark gap that allows any remaining overpotentials to jump directly to ground before entering the high voltage windings of the transformer.

Keeping the RF spikes out of the transformer secondary windings is the name of the game here.

Dr. Resonance



Original poster: otmaskin5@xxxxxxx
After putting together a Terry filter & wiring it into my TC, I started wondering what this thing is supposed to do. I know, this might have been a better question to ask before I built it, but sometimes that's how I do things. Actually I pretty much know WHAT it's supposed to do, but I haven't been able to find good basic level info on HOW it does what it does - i.e., what each component does. I mean basic layman level sort of like Terry filters for dummies. I understand the safety gap part pretty well. But not the other components. For example I know how a capacitor works, but I'm not clear on how it protects the NST.

Any way, I'd appreciate any info on this that any of you would like to share. Thx, Dennis Hopkinton MA