[Amps] re Reduction of 50hz hum via metal plate

[Merv Schweigert]

>     I don't figure why, but (here we also have 50 Hz line frequency)
> with many transformers  we have hum, adding a thick (1.5 mm) carton
> between transformer and chassis completely solve the problem; in extreme
> cases, adding rubber grommets between mounting and chassis fix the rest.
> That of Aluminum is new for me.  Maybe sone sort of mechanical resonance?.

Probably any material that spaces the magnetic field of the transformer
away from coupling into the steel chassis would work,  aluminum being non
ferrous should work as well as a carton, and stronger.  If you bring a
piece of steel close to a magnetic field there will be "vibration", so its
probably just the idea of creating a space with a non ferrous material.

Merv K9FD/KH6