guitar speaker/tube challenge redux

[Magnus Danielson]

From: Christopher Jeris <cjeris at math.mit.edu>
Subject: Re: guitar speaker/tube challenge redux
Date: Wed, 1 Dec 1999 16:46:22 -0500 (EST)

> > >  If you do something wrong to a tube amp, either a cap or a transformer
> > >  will blow, tubes die slowly (my own experience and that of my amateur
> > >  radio collegues, perhaps radio tubes behave different from "audio"
> > >  tubes?).
> 
> Very dumb question - maybe I need to back up a few posts?
> How does a transformer "blow"?  I mean, what happens to it?

Thermic overstress on wires, the wires usually blow up into a open curcuit
on that coil. Ther thermal overstress causes parts of the insulation to
quickly into gas state while the rest have just been transformed into a
mechanical stress due to physical expansion caused by the heat. This forms the
basis for an erruption, a bang, a blow... and all of a sudden you can smell
a combination of ozone and various other unhealthy gas form of plastic burn
residues.

> The word "saturate" that I have seen appear suggests that the core
> material has an intrinsic maximum magnetization or field-strength through
> it - is this right, and what happens to the material when it is exceeded?

When the core saturate you more or less hardly (depending on the core material)
reaches an area where the core no longer contribute to inductance better than
pure vacuume (it does come abrupt to that, but this is what it approximates).
This is part of the nonlinearness that an core based inductor have
intrinsicly. Those, the small scale inductance is diffrent at saturation than
at "rest". So, from a physical point of view you have managed to get all the
spins oriented the same direction of the core iron atoms when you have
saturated, there is thus no more orientations to tweak right and then it
behaves as vacuum for the rest. Now, as you are turning the iron atoms you
can have more or less mechanical stress as well as more or less "friction".
The friction translate to material loss while the mechanical stress is
basically what forms the curve stiffness and thus the relative inductance
constant of the material.

Cheers,
Magnus