Re: I disassembled a vcr... and " what the hell?"
Mu-metal is a nickel-iron alloy (75% nickel, 15% iron, plus copper and molybdenum) that has very high magnetic permeability. Permeability is represented by μ, the Greek letter mu.
The high permeability makes mu-metal very effective at screening static or low-frequency magnetic fields, which cannot be attenuated by other methods.
Mu-metal requires special heat treatment — annealing in hydrogen atmosphere, which reportedly increases the magnetic permeability about 40 times. The annealing alters the material's crystal structure, aligning the grains and removing some impurities, especially carbon. Mechanical treatment may disrupt the material's grain alignment, leading to drop of permeability in the affected areas, which can be restored by repeating of the hydrogen annealing step.
Mu-metal is very expensive and its doubtful that its in any VCR. The high magnetic permeability core of which you speak is called ferrite. This is part of the electromagnetic recording head. There are 2 recording heads and 4 recording head VCR systems out there. These heads are located inside a rotating drum, called a Head Drum Scanner. The rotating head scanner Drum has a top( which rotates) and a bottom (which is Stationary). In the rotating top section there two recording head systems. The heads are located 180 degrees apart, in a 4 Head Drum Scanner they are positioned 90 degrees apart. The 4 head Drum Scanner (and 2 head Drum Scanner) Rotates at a speed of 1800 RPM. In order to get the signals from the electronics of the VCR to the rotary head(and ultimatly the tape) the method of (rotating) transformer coupling is used. The Stationary section of the drum holds the primary windings and the rotating upperdrum contains the secondary. Ferrite shaped core pieces hold the windings. The low reluctance path provides good magnetic coupling. In recording, the signal is connected to the stationary winding as the primary, with magnetic coupling to the rotating secondary winding. In Playback, the rotating winding acts as the primary, coupling the signal into the stationary winding, which acts as the secondary. I believe this is what you were talking about. I understood what your question was right from the start but because of extreme tiredness (from exhaustion) I was trying to wake myself up with a little levity.. No offense was intended.
Regards from (A pretty good deal for 20 bucks, huh) SpectraBEI