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Re: [TCML] Terry Filter

Jim -

I had wondered about the inductance of large wire-wound resistors when used
in a Fritz Filter, and initially tried to find some non-inductive resistors
(monolithic "Carborundum" style) when I was building the filter for my 15/120
system. However, I was never successful in finding any surplus non-inductive
resistors with a value anywhere around 1K ohms, so in the end I just used
conventional wire-wound power resistors.

In answer to your question, I measured the inductance of several 1K ohm Dale
wire-wound resistors that I had laying around using a Sencore LC75 inductance analyzer. (I couldn't immediately locate my own Fritz Filter with its 1K/100 watt Ohmite resistors.)

Length dimension is the actual winding length of the resistance wire, not the overall resistor body length.

1K ohm 225W 9-1/4" long X 1-1/8" dia 160 micro-henries

1K ohm 55W 3-1/4" long X 3/4" dia  175 micro-henries

I was a bit surprised that the inductance values happened to be so close, given the large difference in resistor physical size.

I'm not sure what you mean by "reverse RMF"; did you mean "back EMF"?

Scott Hanson

----- Original Message ----- From: "Jim Mora" <jmora@xxxxxxxxxxx>
To: "'Tesla Coil Mailing List'" <tesla@xxxxxxxxxx>
Sent: Monday, December 31, 2007 12:40 PM
Subject: [TCML] Terry Filter


I am curious, has anyone ever measured the inductance of a 1K 100w Ohmite
resistor? I don't know if they are inductive canceling. The two inch spark I
got while adjusting my unloaded Terry Filter is still a mystery. The gaps
were 1/8" each at the time and the center was grounded to the neon and

I am thinking reverse RMF from ramping up the variac too fast???


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