guitar speaker/tube challenge redux

[Harry Bissell]

When the "core" saturates, the magnetizing inductance of the transformer goes from
large (iron core) to very small (the same coil as an air core)... this makes the
value of the impedance look a lot less than normal (like close to the DC
resistance) and current suddenly goes through the roof... At the same time the
"double whammy" of that lower inductance value will not oppose the flow of AC
current (the step change is very high frequency AC current)

Then all  hell breaks loose.

Harry (been there done that) Bissell

Magnus Danielson wrote:

> 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