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