Dear Dick, Jim,

 

as Jim pointed out, the flux density B scales inversely with the number of turns. As hysteresis losses go up with the cube of B, I would definitely tend to to stay well below 50 millitesla. I use a similar N30 core with 30 turns primary, it stays perfectly cool at 250 watts. Leakage inductance is not so much an issue for a narrowband LF application and can be minimized by multifilar winding. You will have to use thinner wire, but in your tapped autotransformer configuration copper loss will not be excessive.

 

73 and good luck

Markus

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There is a trade-off involved in the number of turns - increasing the number
of turns reduces the flux density and so the core loss, but increases the
loss in the windings. Also, having a large number of turns makes the leakage
inductance higher, and a small number of turns makes the winding inductance
too low.
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