[ARC5] power supply hum

[elden meyer via ARC5]

Les,

Since you notice hum before the tubes have warmed up,
the 12A6 should not yet be drawing plate current. In that
case there are other possible sources  of AC getting
into the audio.

Depending on their relative locations there can be magnetic
coupling between the power and audio transformers. I
learned about this the hard way :)

Also there can be voltage drop in a wire or ground connection
common to power and audio circuits.

Elden