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Dynaco ST-70 buzz from unit


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Last evening I heard a buzz from the amp, NOT through the speakers. It stopped when I turned the amp off, of course but just to emphasize that the buzz was NOT through the speakers. I am running it now with no buzz. What should I look for? It is stock original. Thanks.

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I am going to guess that it is a loose lamination in your power transformer. You probably had been running it for quite a while and it was pretty hot. If you have the cage installed, you might consider removing it.

Another thought is that your filter cap is beginning to break down and is drawing too much current. That, also, can cause transformer buzz. If you start blowing fuses, shut it down until you replace the electrolytic.

Also, check your bias setting and also inspect the EL34's for red spots on the plates. Gassy tubes can sometimes draw so much current that the power tranny will hum.

Hope this gives you a starting place.

FATHER BILL+

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