It could be either 60 or 120 Hz. What is usually called hum are the
harmonics, not the fundamentals, since our hearing is much more sensitive
to the higher frequencies, 400 to 1000 Hz or so. 60 Hz and 120 Hz
harmonics sound very similar.
73
Bill wa4lav
At 12:22 PM 4/20/2006 -0400, Will Matney wrote:
>Peter,
>
>He said though, "60 cycle?". He isn't for sure what the frequency of the
>hum is. With one diode open, you would essentially have a half wave power
>supply only conducting on every cycle. If you have a filter going bad to
>the point it isn't filtering the AC, then you would have a 120 Hz hum. The
>hum would grow greater under load because the filters aren't charging up
>to support the supply. Thus, you'd have a greater voltage drop since the
>filter caps control the voltage sag along with the transformer. If the
>filter caps were all good, and you put a half wave rectifier to them, I'm
>not sure it would sag that much. I would check to make sure that the
>screws used to mount one of those panels didn't puncture the side of a
>filter cap since his problems started after applying the wood panels. A
>screw could have cut a trace in two on a PC board, or could have damaged a
>wire inside. I just can't see a rectifier going open just setting.
>
>Best,
>
>Will
>
>*********** REPLY SEPARATOR ***********
>
>On 4/20/06 at 11:39 AM Peter Chadwick wrote:
>
> >Like Peter, I would suspect one of the diode stacks has gone open
> >circuit. If it was the filter capacitors, the hum would be 120Hz.
> >
> >If it was the cat, the hum caused by purring is modulated at a lower
> >frequency!
> >
> >73
> >Peter G3RZP
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>
>
>
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