Re: [TCML] Terry Filter Resistors

[FIFTYGUY@xxxxxxx]

In a message dated 1/30/09 10:37:14 P.M. Eastern Standard Time,  
bartb@xxxxxxxxxxxxxxxx writes:

>I  don't think any tests are needed as the manufacturer has listed the L  
>for us. I wouldn't even waist my time with it now unless you feel you  
>want to verify.

    It amazes me how nobody here seems to check the  archives first:
 
_http://www.pupman.com/listarchives/2008/Aug/msg00413.html_ 
(http://www.pupman.com/listarchives/2008/Aug/msg00413.html) 
 
    I run four identical resistors total in my Terry  Filter for my pig. Two 
in series on each leg, one mounted at the pig, one down  under the coils. My 
theory is that a secondary strike to the primary feed lines  will at least be 
partially mitigated by the resistors in each direction  - wishful thinking! 
Resistors are Memcor 125W 68 Ohms each, part number  RW12V680. These are the old 
"ferrule" style, popular with the military (and high  frequency/high voltage 
equipment!), and mount like cartridge fuses in clips. 
 
    Funny how somebody finally went to Ohmite  for tech info, but if you look 
in the bottom right corner of the Ohmite home  page, there's a link to 
"legacy literature" for the old Memcor-TruOhm  catalog:
 
_http://www.ohmite.com/catalog/pdf/memcor-truohm.pdf_ 
(http://www.ohmite.com/catalog/pdf/memcor-truohm.pdf) 
 
    I think this old catalog is much more interesting  reading than the 
Application Notes in the main Ohmite catalog! There's even info  in there about the 
inductance of the resistors, but it seems their  attitude is "if you're not 
looking at non-inductive resistors, it  doesn't matter". Also interesting that 
it seems their non-inductive resistors  are at least dual-layered. 
 
    Anyhow, I figure the source impedance of a NST is  ten times higher than 
a Pig's, the operating frequency of a NST coil  is roughly five times my Pig 
coil's, the Terry Filter resistance for an  NST is about ten times what I'm 
using for my Pig, and I'm using much  bigger Terry caps with my Pig. So if the 
inductance of the NST resistors is  100 times that my Pig resistors, no big 
deal! 
 
    Thanks again, Terry, for designing the filter in  the first place. Cheap 
insurance, and as the archives show, using your filter  has definitely solved 
some incredibly bad transient problems that I had. We'll  probably never know 
how much equipment (or even lives!) your filter has  saved.
    

-Phil LaBudde
Center for the Advanced Study of Ballistic  Improbabilities
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