Permanent Magnets and Coils

[BEP]

While shopping the local HamFest for wire and parts I found something that may be of interest to some.

I stumbled upon a choke coil with a magnet on top. The coil was of solenoid type with a plastic form. It had only a few turns of what Americans call 'Litz wire'. (German definition is different)

I asked the old gentleman, selling the parts, 'what was it for? He said it was a tricky little idea to save on the expensive wire used in high quality audio chokes. The magnet raised the Q, increased the inductive reactance and prevented saturation using much less of the expensive wire. I told him the idea of the inductance going up because of a magnet sounded wrong. He said 'not the inductance - the inductive reactance. The inductance goes up because the magnet acts somewhat like a core but that isn't what I mean.'
He explained the reactance went up only when there was a signal.
He is a proud 84 and has forgotten more than I'll ever know.

Stick a round magnet on the end of a coil and see? Maybe I will.

[BEP]

It certainly has a good effect on flyback (BEMF to most - not that I think that is the correct term) AND CEMF!

I get very similar results with a little DC bias current added to the coil (when without the magnet). It takes a lot of current to have the same effect.