In Reply to: Where from that hum?? posted by vinnie2 on September 11, 2016 at 14:13:25:
Thanks for all the suggestions folks, it allowed me to find the problem. It's the filament supply on the 26's, which still have AC on them.
I found a neat little tool called the "on line tone generator" on the net. It lets you generate a steady tone and to generate multiples of that tone with a mouse click. It was real easy to flip back and forth between 60 and 120 and hear the difference. That was enough to tell me my hum was 60 hz and was therefore coming from a filament supply. I went back to the first 26 and tweaked the hum pot very carefully until I got it as low as I could by ear, and then I checked it again with the dvm and it was down to 20mV. That's a big decrease from 110 I got the first time, so I think if I put in a 10 turn pot on each 26 and adjust them by watching the dvm to get the lowest reading on each I just might get there. I will report back after I try it.
Edits: 09/12/16 09/12/16 09/13/16
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Follow Ups
- update 2 - vinnie2 07:04:43 09/12/16 (2)
- RE: update 2 - Tre' 09:13:53 09/12/16 (1)
- RE: update 2 - vinnie2 15:56:36 09/12/16 (0)