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Cathode and other types of feedback
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Old 28th March 2006, 07:44 PM   #21
Johan Potgieter is offline Johan Potgieter  South Africa
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Thanks for broadening my horizons.

I guess, being fortunate enough to have moderately reasonable transformer winders locally, thus making it economical to design and obtain my own few transformers, I have been suitably shielded from the wicked world out there. With our economy imports are comparatively expensive and local stocks of tube output transformers non-existing, so..... (Btw, I did not question that there are differences in winding resistance, just how that could cause different inductances - but not to worry. With what you mentioned, anything is possible.)

And I have also been looked upon quite strangely for suggesting that THEIR own output transformers are not suitable for hi-fi work, because, see, they work quite well in PA amplifiers!

Sic transit gloria (and us veterans).

Sorry if this was a bit off-thread.
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Old 28th March 2006, 07:54 PM   #22
SY is offline SY  United States
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Let's use a simple model. The inductance of a solenoid is proportional to the square of the number of turns and the cross-sectional area. With a layered winding, the number of turns in the two halves may be equal, but there will be a difference in the area between the inner and outer layer. So perhaps that's why the two halves show a different inductance?
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
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Old 28th March 2006, 08:42 PM   #23
Johan Potgieter is offline Johan Potgieter  South Africa
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SY, me friend....

Yes, OK! One does forget basics sometimes!

One tends to think that with iron-cored products this does not really matter, most of the flux being concentrated in the core anyway - but there!

Though I have checked in the past and cannot recall finding much of a difference, you will now have me burn midnight oil (locally) and go and recheck on the few output transformers in my possession. I think more than likely my own designs will not show much difference because I sectionalise, interleaving also primary windings, but I have a few of the type described by Tubelab.
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Old 28th March 2006, 08:59 PM   #24
EC8010 is offline EC8010  United Kingdom
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Further, an outer layer will have a different leakage inductance to an inner layer, because leakage inductance is just that - it's flux that was lost on the path from primary to secondary, and that's the real problem. The problems with cfb turn up at HF. Sadly, most transformers are constructed as Tubelab describes - it's most unusual to find transformers that are properly balanced.

If you don't believe me about leakage flux, try waving a search coil near an output transformer. The places where you pick up the most signal are on axis of the coil (as you'd expect) and at the edges of the coil.
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
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