The "Terry filter" (was NST deaths on async gap)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Mark Broker by way of Terry Fritz <teslalist-at-qwest-dot-net>" <mbroker-at-thegeekgroup-dot-org>

About 1uH: that's nice to know :)

I concluded (perhaps falsely) that the resistance was inhibiting accurate 
inductance measurement with the meter I was using because the meter gave me 
two very different values depending on 120Hz or 1000Hz measurement.  I 
don't remember any more details than that, since that was better than 3 
years ago.  It does appear that your meter reads a little "off" as well.

Regarding the NST deaths with your filter design: I can claim 2 such 
deaths.  The first failure was "operator error," (major system changes, 
completely new environment, and neglected to reset my safety gaps) and the 
second one was a faulty NST - it looked "very well used" and featured a 
broken LV bushing.  Interestingly, the "bad" NST was hooked up when the 
first one died, and has probably a full hour of TC service.  The filter was 
the original design posted ca Jan 2000.

Regards,

Mark Broker
Chief Engineer, The Geek Group


On Sat, 09 Aug 2003 16:48:53 -0600, Tesla list <tesla-at-pupman-dot-com> wrote:

>Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
>
>Hi Mark,
>
>At 10:05 PM 8/7/2003 -0500, Mark Broker wrote:
>>...
>>
>>The wirewound resistors in Terry's filter design do have a fairly large 
>>inductance.  I remember trying to measure it once (the 1kohm, 100W 
>>Ohmites), but the RLC meter I was using had issues with the large 
>>resistance, and wouldn't give me reliable results.
>
>I measured one of the Ohmite L100J1K0  100W 1K ohm resistors here.
>
>I get a DC resistance of 1000.88 ohms (pretty good for a cheap space 
>heater resistor ;-)) and an inductance of 884nH.  I resonated it at 307kHz 
>with two 0.15uF caps of our favorite kind ;-)  I used the HP signal 
>generator and Tek scope to resonate the set.
>
>The Elenco LCR-1801 gives 997 ohms at 1.121uH.
>
>At say 250kHz, 1uH has a reactance of 1.57 ohms.  Insignificant in terms 
>of the filter's operation.  So I think it is safe to say the series 
>inductance of the resistors is insignificant in the filter's case.
>
>Odd that it messed your meter up, but some LCR meters don't like series 
>resistance at all when measuring inductance.  Depends on how they work 
>inside...
>
>Cheers,
>
>Terry
>
>
>