wired
New Member
Posts: 2
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Post by wired on Aug 27, 2008 5:11:07 GMT -7
Hi. I have an older KT-45 which has a low pitched hum when idling. It is affected by the volume and the interactive treble in this design. It is not affected by a guitar, pickups etc. I have checked all the grounds which are OK. I've tried biasing the tubes on the cold side and maybe it helps a little like turning the volume down a bit. It doesn't seem to matter which tubes are in it either. Suggestions? Thanks, much. John
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Post by DRZ on Aug 27, 2008 5:44:42 GMT -7
I doubt that tranny is humming as it would be a mechanical vibration type noise and wouldn't be affected by input volume pot setting.
My best guess since the 45 has no negative feedback that you have a mismatched set of EL-34's , that's why biasing them cold lessens the hum.
Get a VERY good MATCHED set of EL-34's and try again.
DR.Z
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wired
New Member
Posts: 2
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Post by wired on Aug 29, 2008 20:06:12 GMT -7
Hey, thanks so much for your reply. I tried tubes that were matched within 0.1 ma and the hum persists. When playing, you barely notice it if at all, but when quiet or in between notes it is there. Sound almost like barber clippers, but a little lower in pitch. I think the cold bias brings the overall volume down and makes it less noticeable. Suggestions? Thanks. John
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Post by bluzman on Aug 31, 2008 20:40:53 GMT -7
A few basic things. I've run into trouble with Electric Fences, Invisible Fences with and without a guitar plugged in. Neon lights and light dimmers and fan speed controls usually with single coil guitars plugged in.
Also I have a second floor studio. The first floor is a shop with fluorescent lighting. I need to turn those lights off when I use the studio as it does affect some of the amps as the ballasts are within 12 Inches below the amps and the wood flooring doesn't shield the interference.
Pre-amp tubes OK?
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