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In Reply to: RE: At the risk of assuming.... posted by op48no1 on January 29, 2015 at 19:30:24
...and let Excel do the heavy lifting. And now seeing what Tre' is really attempting to do (not a simple RC hipass), it seems Dave Slagle's method is probably best. Never Assume!
Follow Ups:
If you want an accurate measure of a transformer's L then there is no replacement for using an inductance bridge.The question I have in using Dave's suggested method... is all of the current so measured the result of just the load presented by the L? Does it isolate the other transformer losses (loads)?
Also Dave's suggestion of using say 10 volts at 60 hz is a good start.
If measuring L you want to excercise the iron pretty well--- the L will generally keep increasing as the emf force is increased up to the point of it hitting the knee of the BH curve. So you might also want to try
some larger drive voltages (again keeping the frequency at 60 hertz or less).If you want to get toward what is often called OCL (open circuit L) then you might want to measure the L at the transformers full rated power. Using ohms law you can derive the volts necessary to drive the nominal primary impedance to full rated power. Doing this at 60 hertz should not overload the primary since most audio transformers are going to rated at frequencies lower than 60 hertz.
But, again, an inductance bridge is the best tool for these measurements.
MSL
MSL
Builder of MagneQuest & Peerless transformers since 1989
Edits: 01/30/15
Nothing to argue with in what you say but now that we better understand Tre's objective, I would think Dave's proposal ought to serve the purpose. It would be another matter if Tre' was attempting to thoroughly characterize his OPT but I don't think he is. Interestingly, the method Dave proposes is virtually identical to the method D.T.N. Williamson suggested to verify the inductance of his OPT design for the "Williamson Amplifier" when it was constructed by DIYers in the late 40s of the previous century.
Yeah. My feeble attempts to use simple models to extrapolate transformer parameters have never met with much success. I agree with your comment about Dave's method.
Of course, the politically correct response is that Tre should just lash it together and see how it sounds...
-Henry
...but not before grafting on triple leads of Kimber TCCS for each stock lead. ;-)
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