Thanks Martin, Tom, Ken and Clive (off reflector) for your responses.
Clive said "what you have is what is left of a sintered neobium magnet
that has simply disintegrated over time. They simply had a limited life
in their infancy and now following a lot more research and design and
attention to the manufacture of the materials, their life is virtually
unlimited."
I found that the outer shell is non magnetic. After removing as much of
the loose material as I could, I can see that the magnet is in the
center. It is mostly still there, and is a sort-of lozenge-shaped piece
that has the appearance of a ferrite or powdered-iron core. There
appears to be no actual pivot as such. The moving coil is suspended on
a taut fine wire that runs straight through a small hole in the center
of the magnet from a front support to a rear support. This taut wire
locates the coil and provides the spring force. Unfortunately even
though I've removed all the loose magnet bits around the coil and it
looks like it should be completely free to move, there must be some bits
in the hole with the wire, and they must be preventing the wire from
twisting and untwisting freely.
So I now have a meter movement that mostly works. It appears to have
approximately its correct 1-mA sensitivity -- a 9V battery in series
with a 10k resistor swings the pointer most of the way over if I help it
past the sticking points. Then, I get to help it again on the way back
to zero after I remove the current source. So this won't do. Even if I
work at it and get it working, I'm sure once I get it all back together
it'll stick again. The innards appear to be press-fitted inside the
outer shell, and resisted my attempts at pulling them apart.
Harbach Electronics doesn't list the meter on its Web site, but I sent
an e-mail.
73,
John, W1JA
----- Original Message -----
From: "Martin AA6E" <aa6e@ewing.homedns.org>
> John,
>
> If you're lucky, it might just be some magnetic dust that found its
> way
> onto the magnet, and the magnet might be OK underneath. I've never
> heard of magnets disintegrating.
>> John Pelham wrote:
>> I have a Heathkit SB-230 amp (it's the fanless one that uses an
>> 8873).
>> It has been in storage for 15 years (inside the house living space,
>> heated and air conditioned). I just got it out, and found that the
>> meter pointer was stuck at zero. I disassembled the meter and found
>> something very strange. The moving coil is there, and in the center
>> is
>> what I assume is (was) a permanent magnet of some type. This magnet
>> has, while in storage, decided to partially or completely
>> disintegrate
>> into tiny shards of magnetic material. It has grown outward to
>> partially surround the coil and, I assume, the pivot, which may be
>> why
>> the coil and pointer won't move.
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