[ARC5] power supply hum

[WA5CAB--- via ARC5]

Les,

Pull the 12A6 and see if you still get the hum.  If you do, its source 
should be pretty simple to find.

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

In a message dated 01/22/2015 07:24:02 AM Central Standard Time, 
arc5 at mailman.qth.net writes: 
> 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