OT: demagnetization

[Tony Duell]

> 
> 
> Can someone point me to schematics for a decent homebrewed demagnetizer?
> I've accidentally magnetized a bunch of little parts that really shouldn't
> have been.


The normal method of demagnetisation is to subject the part to an 
oscillating magnetic field that uou gradually reduce the amplitude of.

Typically the last part is done by pulling the part away from whatever is 
generating the field.

I don't know the parts you need to demagnetise, but a typical home-made 
demagnetiser soncists of a medium-sized mains transformer that the core 
has been removed from, and then all the 'E' laminations re-iserted facing 
the same way. You connect it to the mains with a light bulb in series 
(the inductance will be much reduced by the open core, so the impedance 
will also drop and the current go up), then put the parts on the open 
face of the core, turn on the current and pull the parts away to arm's 
length. Only then do you turn it off.

Can you still buy tape bulk-erasers? That would work too.

Old books on watch repairing have various designes for demagnetisers in 
them. If the book is old enough, it won't assume the availabity of AC 
mains. There were designes using vibrators (no, not _that_ sort of 
vibrator, the thing that was used to chop the DC supply from a car 
battery in a car radio so you could feed it into a step-up transformer 
to get the B+ for the valves). There were designes using rotating
permanent magnets (and woe betide you if they came loose!).

-tony