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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Waste-free core posted by sser2 on February 12, 2006 at 16:54:46:
"... for a choke there is no such thing as stray inductance. "Careful. I admit that the notion of leakage inductance doesn't quite fir into the usual model of a choke. But, if you think in terms of coupling instead leakage inductance (just different ways to look at the same thing) then it becomes apparent that each winding in a choke doesn't necessarily couple with every other winding. The ideal choke has inductance proportional to N2, but that assumes perfect coupling between all windings. Imperfect coupling implies less inductance.
More to the point, in the case of PP with grid chokes, you can double the inductance of each choke by winding both coils on a single core (or use √2 fewer turns to achieve the same inductance.) The 2X inductance assumes identical signals (180 degrees out of phase, of course) and perfect coupling between the two coils. With imperfect coupling you'll get less than 2X inductance in each coil.
Then there's the fact that coupling tends to reduce any imbalance in signals. Hence the idea that a 'ct choke' can turn total imbalance (no signal at all at one grid) into balanced drive. I suppose one way to look at it is that the needed amount of balance improvement determines the amount of coupling required. Any more than that results in an unnecessary compromise.
Again, this is all according to first order theory. More complicated effects like sum and difference artifacts require more sophisticates analysis. In the end, the proof of the pudding is in the eating.
-- Dave
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Follow Ups
- Re: Waste-free core - Dave Cigna 18:05:11 02/12/06 (2)
- Cannot but agree, great insight into coupling in choke. nt - sser2 18:21:40 02/12/06 (1)
- Just to add a little more complication - - J Epstein 19:02:43 02/14/06 (0)
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