Noise coming through speaker changes when plugged into the wall

[Holmz]

thanks can there be a ground issue with the power cord that interacts with the tube amp? There are three brand new power cords I am testing so I doubt all three have a problem but they are all causing the same noise. Very strange indeed. jh

Well - it could be the amp.

But at this point the high-$ cord is the worst performer.

 

[EERecordist]

In radio a tuner is a downconverter. The simplest radio receiver was a crystal radio. So inside any electronic device that is not properly designed, a transistor can downconvert RF to audible. It is possible for poor/corroded physical connections to act as a downconverter.

Interference heard in the tweeter if likely due to switching power supplies or RF downconversion. Heard in the woofer, it is more likely to be improper power supply filters or bypass capacitors, a design problem; or ground loops.