Re: {Collins} 75S-3C Audio Hum



This Group is great !!

I have a 75S-3C like Paul, but haven't noticed any hum.

But if I ever hear any hum, I now have a good starting point for troubleshooting.

Thanks All !!

W4DNR  Don


Quoting Paul Christensen <w9ac@xxxxxxxx>:

Thanks for the suggestions, including Fernando's, who got me thinking more about V8, V11, and the subsequent audio stages.

The problem was V11, the BFO. I went through six 6DC6s before finding one with no hum. For whatever reason, a GE works best. Several Phillips and RCA branded tubes produced the most hum. On the GE, I hear a brief moment of hum at initial warm-up, but then it quickly fades away to zero.







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