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So, I go away for my job each summer, and unplug my system completely from AC when I do. I returned earlier this week, and my Scott 850D now has a persistent low volume hum - it sounds like about 60hz. I didn't change any connections, other than unplugging from the wall. It did not have this when I left in June.
This Scott has a selenium rectifier.
Any ideas?
David
Follow Ups:
I would also clean all your RCA interconnections - both at the cable ends, and on both the tuner and next stage. A hum is a very common sign of poor ground connections on one or both phono plug cables.
Also try reversing your AC plug in the power socket, if it can still go in both ways. The original power cords could, and usually one position had better audio performance (less hum).
I would also check the voltage from the selenium, again, if still in there. I can't imagine Foster Blair did not replace it. He usually does Maple Shade Scott tuner work. Not sure that is still true now that he's moved.
Ours are 3 pins and can't be swapped over.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
It's possible that the selenium rectifier is going off. Or a cap is fading.
But, clean and tighten all connections, at both ends.
And then take out and replace all the valves, after cleaning the pins. I'll assume they're all novals!
If hum's still, have someone replace the rectifier with something quiet, soft-recovery and high voltage! And, check the filter caps, too.
IMO Mapleshade should have replaced it back when.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Thank you. A cleaning - one tube at a time - is the place I'll start.
David
A soft-recovery ss diode with a high voltage rating.
Eli Duttman's posts cover this.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
I've 'fixed' many malfunctioning (elderly) FM tuners by cleaning pins and/or sockets on the tubes, indeed! That said, for the OP's benefit: if you decide to go this route, remove, clean, and reinsert tubes one at a time . There are numerous carefully tuned circuits in an FM tuner; each circuit is tuned to the tube in that section. In many tuners, there are multiple 'instances' of the same tube type (e.g., 6AU6). Inadvertently 'swapping' different tubes of the same type between sockets may profoundly, and likely negatively impact performance of the tuner.
all the best,
mrh
So, 'valve' is more descriptive, and apt. :-) and ;-)!That selenium diode (rectifier) should go, too!
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 08/12/19
I was able to find zero information on what a Scott 850D is. When's the last time the capacitors in the power supply were replaced?
If the electrolytic capacitors are dried out, the surge after a period of dormancy could have taken one (or more) out.
That's because I wrote "850" instead of the correct "350 D" as I should have. Sorry about that. It was completely refurbished one year ago by Mapleshade (which means a gentleman who is a Scott expert whose name I forgot).
It was sounding great as I left, and now still sounds great, plus a low level hum that occurs with none of my other sources. I suppose that even though it was refurbished, it could still have a bum tube.
No need to be sorry, typos happen.
Timbo and mhardy6647 have given you some good advice above, as to where to start. Good luck with it.
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