[Minter]

The older tempests that had the hum issues: has anyone tried to locate the transformer outside the unit in a seperate power supply case?  Isn't the transformer the problem, as the newer ones have the mu shielding or do the issues go beyond the transformer?

[Will]

I had a hum issue with the basic transformer, and later with the mu shielded transformer.  A (now discontinued) PS Audio UPC-200 Humbuster made the hum disappear. 

Klaus went beyond the call of duty trying to solve the issue, swapping out parts many times.

The transformer hum was apparently caused by DC in the lines (the Tempest is sensitive to dirty power).