Slight hum in my amp. Is this normal?

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atmasphere

You can have DC on the line and oddly enough, it can be passed through transformers.

Please explain.

@atmasphere thank you for chiming in on this thread.

@jea48 , I thought I did. One more try:

DC on the line occurs when 1/2 of the AC line (for example, positive going portion of the AC waveform) is loaded while the other half is not.

Space heaters or hair dryers on half power do just exactly that. So one half of the AC line can have lower amplitude due to the loading as a result.

But its still an AC waveform and so can travel through a transformer. But the output will still be asymmetrical. The asymmetry can be filtered out by a DC blocker which is a simple circuit consisting of 2 or 4 diodes that are bypassed by some large capacity electrolytic caps.

For a well made amp this is not normal.

Go under chassis, remove the transformer screws, apply some blue tac or similar substance to the holes and re-tighten the screws. It will lower transformer noise.