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Output - not Power - Transformer Buzz

So, a few weeks ago, I replaced a friend's ST70 power transformer with the 240 volt replacement from Triode and mailed him his amp at his new home in Spain. He has owned and used this ST70 for decades and it has always suffered from mechanical buzz coming from the power transformer - a common, well-known problem. We hoped that the new transformer would run cooler than the original and be silent. Short story is that he got the ST70, hooked it up to his spendor speakers and fired it up. It sounds glorious, according to him. But there is still mechanical buzzing, except this time the buzzing seems to be coming from the output transformers. In other words, he lays his hand on the power Xfrmr and it has no vibration; he touches the output transformers and they seem to be vibrating. This st70, just for the record, was extensively modified many years ago. The board uses a pair of 12ax7s and a pair of 12BH7s. I do not recall the brand-name of the board. The 5ar4 has been removed and replaced with a solid state rectifier. Otherwise, all is pretty normal. Anyone have any experience with this problem? Can anyone recommend a testing protocol to trouble-shoot this? As it stands, the buzzing is not as annoying as the old buzz from the power transformer. Still . . .


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Topic - Output - not Power - Transformer Buzz - funkwrench 10:48:03 06/09/15 (0)

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