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Hum issue
#1
Hi
I have a firefly PCB build that started out fine but has developed an intermitant slight hum. The odd thing is if I touch the transformer (power) case with my .finger the hum goes away. Anybody have any ideas?

Thanks, TB
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#2
Set up a volt meter across the amps output set for low A/C volts and view the meter with the amp idling, does the meters A/C idle voltage reading go up when you hear the hum?
If not than its a machanicle vibration, as all power transformer vibrate at 60 cycles, if this is the case than make sure the PT is bolted down good, or if its the type in a complete metal case, make sure the case is wraped up good around the PT.
Sometimes all you can do with this small type of cased PT is to unfold the wrapper crimp tags, smear some black silicone sealer in there, and fold and crimp it back up and bolt it back in the amp.
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