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Normally, calculating and winding mains-transformers shouldn´t be a difficult thing, it has only to work for the specified mains frequency and has only to supply the valve amplifier with right voltages. But transformers efficiency depends on core and copper losses. Calculating mains-transformers with maximum allowed induction will save money, on the other hand will give high overtemperatures, high core losses and a high magnetostriction effect. All ferromagnetic materials will undergo a small mechanical change when magnetic fields are applied, either expanding or contracting slightly. The more higher the induction, dest more largely this effect, resulting in the well known mechanical transformer hum. Minimizing these negativ points, means nothing else as to reduce induction by using annealed low loss M6X core, which is on the other hand more expensive. Several tests pointed out, only to allow inductions up to 1,2 Tesla (78000 lines/sq.in) at smaller and up to 1,0 Tesla (64500 lines/sq.in.) at greater shell type mains-transformers, using low loss M6X core for getting the best compromises between costs, low overtemperatures, high efficiency and a low leakage field. With these parameters, I´m in the position to manufacture mains-transformers up to 550 VAs, C-Core mains-transformers for higher power ratings will follow. All transformers are vacuum varnished finished and have a screen winding between the primary and secondary coils. |
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