mag amp audio

[CGS2510.SEP.STUDENT.UCA at CUB.UCA.EDU]

Recall the postings about controlling the inductance of a ferrous 
core gadget by applying a dc control to an extra winding...

Well, a trip to a pawn shop reminded me of something that might be of 
interest to somebody.  Carver at one point made an audio hifi amp 
that was a mag amp based item.  I believe the one I read about was 
about 8x8x6 inches or so and delivered a couple hundred watts.  I 
suspect it weighed a lot, but was very effiecient and physically 
small per power compared to the tube amps available at that time.  I 
think this was circa about 1955 or 1960 or thereabouts.
Can anyone elaborate on this?