[R-390] 60 Hz Hum Output from R-390A IF Module

[Roy Morgan]

On May 20, 2009, at 9:03 AM, Jon Schlegel wrote:...
>
> Of more significance is a marked change in hum output for certain
> mechanical filter selections.... hum level drops by about 11 dB just  
> by
> changing from 8 kHz to 16 kHz filters.

Jon,

The filter action depends quite a bit on the filter skirts making good  
contact with the mounting surfaces.  You might be getting "blowby"  
around some filters that is being modulated by 60 cycle hum

By the way, is it SIXTY cycle hum you are getting, or 120 cycle "hum"?

60 cycle would mean heater supply or transformer induced hum.  120  
cycle noise would be coming from rectified B+ having too much ripple  
on it.  Have you measured the ripple on the B+ supply? At various  
points?

Roy

Roy Morgan
k1lky at earthlink.net
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Groton NY, 13073
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