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NST Variations

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Mddeming-at-aol-dot-com>

Hi All,
       While doing preliminary resistance testing on a set of 15/60 NSTs of 
different origins, I noticed a couple of anomalies that might or might not 
have some significance. I expected to find some variation in coil resistance 
among different manufacturers, but a variation in secondary DC resistance of 
up to 32% seemed unusual:
Franceformer: 4696 Ohms, Transco: 5897 Ohms, and Allanson 6612 Ohms. 
       More puzzling perhaps, was the consistent variation between left and 
right halves of the same secondary. For consistency, I defined the "right 
side" as the one with the primary terminals. In France and Allanson cases, 
the right side had 3% higher resistance than the left side. In the Transco 
case right was 5.5% higher than left. Readings were checked at two different 
times with three different meters: Radio Shack 22-174B, Fluke 8000A, Fluke 
8275A with filtering. Repeatability variation was <0.4%. I realize that with 
only 3 transformers there is still a 1 in 8 chance of the left/right 
variation being simple random error. 
       I am wondering if these simple tests could indicate compatibility for 
use in an NST "farm". If so, it could save people time and money (and 
strain). Has anyone else encountered this phenomenon? I will be running AC 
tests this weekend.

Matt D.