Hi Gary,
I tried lifting the ground wire. No change. I replaced the big filter cap.
No change. It's possible there is a leaky cap causing the hum, but short of
replacing all the capacitors in the radio I'm not sure how to find. I've
tried putting an equivalent value capacitor in with each of the
electrolytic caps (one at a time). None had any effect on the hum.
Using a swamping resistor certainly knocks the hum down to a tolerable
level, but running the radio on external 12V clears it up completely.
The radio is working fine otherwise, so I'm reluctant to start replacing
parts that are probably ok.
-Josh
On Thu, Jun 1, 2017 at 8:02 PM, Dukes HiFi <dukeshifi@xxxxxxxxxxx> wrote:
> I am wondering about the outcome of this thread. One should NOT need to
> operate the C-21 from an external supply.
>
> The internal supply is pretty good. If it is introducing hum of the ground
> loop type, why not just lift the ground (green wire). That should eliminate
> ground loops.
>
> If it doesn’t, then there must be a leaky capacitor that is bypassing the
> power lines to chassis.
>
> Gary
>
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