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In Reply to: RE: Phono hum in Scott 222c posted by Triode_Kingdom on August 30, 2014 at 16:43:58
ha, I double checked to make sure it doesn't follow that part of the schematic :)
yes all the tube shields are present, and all of the filters and DC caps have been replaced including 201 and 202, now a 50/50 F&T..cap. I experimented changing the ground of that cap to different locations but no change..
It is hard to tell with hum if it is 120 or 60, I could be wrong..
Follow Ups:
Is this an amplifier you purchased recently (any chance it's been modified)? Other than the hum, does the phono section sound about right from the standpoint of tonal quality? Are both channels humming?
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Buy Chinese. Bury freedom.
no, I have owned this amp for a long time now, no mods other than the usual upped capacitance from the new filters. Coupling and by pass caps were replaced earlier about 4 years ago, along with selenium rectifier..- the usual restore stuff... re-did the DC with 4 Muse 700uf 35v, new resistors in the DC and new resistors in the B+ between the caps. Voltages on the B+ stages are spot on.. I would venture to say however I just got my Turn table out and I don't recall if the phono already had this issue or not. It's possible it was always this way and I never noticed it..
Phono sounds correct other than hum..yes both channels hum..
If I really turn up the volume past 12:00 on the aux or any line stage I can get a slight hum around 1:00 2:00 but this is past the amps usable power and I would never need to turn it up that far ever..Not sure if that is unusual. I have super sensitive speakers 98db, so some hum or noise is bound to come through when that high..
If I turn the volume up past about 8:00 -9:00 on phono however, very noticeable hum occurs..
Well, at this point, I'm pretty much out of ideas for a quick fix. I think you need a scope to measure ripple on the various B+ voltages. Normally, I don't encourage cross-posting, but maybe you should post this problem on the TubeDIY forum. Some of the guys who hang out there also repair factory gear. You might find someone who's more familiar with the day-to-day idiosyncrasies of this amplifier than I am.
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Buy Chinese. Bury freedom.
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