gapped output transformers?

> Google wasn't much help when I tried looking this up.

DC in a wire/coil makes a fixed magnetic field.

A refrigerator (or speaker) magnet makes a fixed magnetic field.

To a first approximation, one can replace the other.

Getting the reefer magnet into a tight magnetic core at the right intensity, may be tough; also it does not respond to changing supply voltage or temperature part-drift. Abbey may someday find it is "the" solution to some problem he tackles, but here I am sure he is joking.

Side-observation: three ways to erase magnetic tape. The good way is AC. Very cheap tape decks used magnets. Often a sliver of Alnico on a pivot, but I think I have seen a wound head with DC switched to it. As long as you get a field, the tape doesn't care how you got it.

Lee_M said:

Hmm, Second primary sounds like a misnomer ???

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I guess we'll have to seek advice from a semiotician...
After all, a winding becomes a primary or secondary (tertiary?) only after it is connected to a circuit. An interesting example of this ambiguity is in the McIntosh amps, where the cathode windings of the OT are both primaries, receiving power from the cathodes, and NFB secondaries, feeding signal to the cathodes.

Google wasn't much help when I tried looking this up.
It sounds interesting, Can you share a little more info?

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It's just something I made up in a flash, but it could probably work, somehow; install a counter-oriented magnet along the flux axis. The magnet may demag over time but it would work long enough to pass the warranty period.  ???

PRR said:

I think I have seen a wound head with DC switched to it.

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I'm sure I've seen it too, in conjunction with DC bias; just found a brief mention in Wiki
https://en.wikipedia.org/wiki/Tape_bias
I guess the rationale was that the cost of a head and a switch was a proper counterbalance for the hassle of making a reliable moving magnet eraser.