Gilbert Bates wrote:

Thanks to all the RATs for previous advice on custom chassis size. I'd like
to ask if given heavy enough gauge ... which is better for constructing an
amp ... steel or aluminum? Do they each have their own merits? Thanks.
Cordially,
west


I'll probably get something wrong here but...

From the technical standpoint, the non-ferrous metal (aluminum) works
better to shield the components from stray (leakage) magnetic fields
from the power transformer and other sources. It is also less prone to
induced currents in the chassis itself from leakage fields.

Turns out that it the other way round. Easy for one to test this concept.

All you need is any common power transformer which you first of all carefully
hook up to the local AC power source. You will also need an output transformer.
You can detect the stray field set up near the power transformer with the output
transformer, preferrably unshielded if you have one. The voltage resulting can be
observed on the high impedance winding of the OPT with an oscilloscope or if you
haven't got one, a set of headphones will do. Sometimes there is so much coupling
you will hear the AC hum on a loudspeaker connected to the OPT output winding.
Once you are set up & receiving the AC hum you can do lots of interesting
experiments to determine the shielding properties of various materials brought
between the pair of transformers.

Another test to try is the orientation of the transformer pair with respect to
each other. If they are to be side by side on the chassis the core orientations
should be mutually perpendicular to get maximum rejection of power frequency hum
set up by the stray field from the power transformer.

Cheers, John Stewart