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Radford Renaissance STA 25 - mains transformer is humming

Hi,

I bought a Radford tube amp last week. I ad noticed no humming at the demo of the amp, whyle listening to the music, but at my home it was there. Between the track pauses I can here it 2 metres away. A constant humming coming direct from the coils. The transformer is isolated by rubber gromets and has already be switched to 240V.
What can I do?
 

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Beautiful amp! Is it possible you have some DC offset in your AC line? That will irritate a lot of power transformers. Can you temporarily try it in a different local? Maybe even a different spot in the house. There are devices that will block DC offset.

It's also possible that the transformer has loose windings or lams, and you just didn't notice the hum in a different environment. You could try tightening the bolts that hold the lams together--gently! Don't try to torque them down but tightening them up a bit might reduce the vibration.