# SE OPT formula question

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#### Paul Joppa

It looks like the missing reference may be to some Hanna curves, which are used to design chokes.

#### Osvaldo de Banfield

It seems to be some kind of Al value, say, an inductance per each 1 turn in the core. The question is where did they took this value. Also, it appears that they didn't took in mind the loose of inductance because of the gap needed to get rid of the DC field in the core.

#### Paul Joppa

On page 4 of the reference, there is this: 'Between part “E”and part “I”paper insulation is used.' I take this to indicate that the transformer has an air gap.

#### cerrem

The IEEE article is severely lacking from all aspects.... They would have received F if I was grading the paper... It's a science project....I would not use this as a guide to design transformer...

#### U130421

These fellows are designing the output transformer as they have learned how to calculate the ferrite core inductor . The datasheet of ferrite cores give the sq,rt Henry/turn , after which you can calculate the number of turns to get the required value. Certainly they put a paper as air gap , wind about ten turns, and measure the inductance to deduce the 1200 value. To have better explanation of how to calculate SE transformers I advise you the Radiotron , free download. Warning. It is not as easy to understand.

#### rcbuck

Yes, I think the table on page 213 of Radtron gives a fair representation of the inductance required for a home made transformer. A practical example is shown beginning on page 216.

#### rcbuck

Another book I have used in the past is Practical Transformer Design Handbook by Eric Lowde. It is out of print so it may be hard to find a copy. The book has step by step design instructions using the standard transformer design equations.

#### GoatGuy

I have … a question … that's been bothering me for years.

What would be the drawback of having either a CHOKE LOAD for the finals, or a auto-adjusting constant-current regulator (ideally 'shooting' for 60% of B+ as the quiescent operating point) then → → high value, non-polar capacitor → standard issue “single ended triode” output transformer … → out.

The idea is, have the quiescent current shunted away from the output transformer, leaving it to “transform the AC signal”, without the DC component.

Especially if a constant current regulator is employed, it seems like an almost (but not quite) perfect fit.

The use of a choke load instead has the advantage of running the triode way closer to its maximum voltage rating (and above!). But still … its more iron, more cost, a lot more mass and space. Might have been the only way to accomplish this before say 1975 or 1980, with the invention of really good CCS's made from FET/MOSFET technology. Depletion mode devices with really, rally flat 'pentode' signatures.