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Post by Matt on Oct 23, 2012 4:31:38 GMT -7
I had a power tube go out on me Saturday and I replaced the quartet with an older set (with low hours). As I was playing for a while I started to notice a weird harmony. The amp was generating some sort of lower frequency sub-harmonic ghost note (not sure what the technical term for this phenomenon is called).
Does anyone know why this would occur and how to fix it?
Any help is greatly appreciated.
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Post by benttop (Steve) on Oct 23, 2012 5:37:19 GMT -7
You changed tubes and the ghost note appeared. Change them again.
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Post by Matt on Oct 23, 2012 6:24:37 GMT -7
Planning on it as soon as new ones arrive but was unsure if power tubes could produce that sort of phenomenon. So the questions becomes can power tubes cause that problem or is it likely something else is causing it?
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Post by headshrinker (Marc) on Oct 23, 2012 8:17:49 GMT -7
Tubes can cause that sort of problem. Especially if they are getting vibrated. If you have a head and cab try separating the head from the cab and see if it goes away. You might also try swapping the position of the tubes. What vibrates in one position doesn't always in another. If you had the amp up loud you might have a speaker thing going on. Try another speaker if you have one. Also try the old tapping on the tubes with a pencil eraser and see if you can reproduce it. Don't forget the preamp tubes.
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Post by Lefty on Oct 23, 2012 19:33:36 GMT -7
I've had a filter cap cause that.
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Post by zpilot on Oct 24, 2012 3:03:56 GMT -7
Yep. Sounds like a bad cap.
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Post by Matt on Oct 24, 2012 8:15:01 GMT -7
Is a bad filter cap hard to replace? The amp is only 8 months old so I'm going to be really disappointed if it's something other than a tube.
Thanks for the help guys.
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Post by benttop (Steve) on Oct 24, 2012 16:23:01 GMT -7
Always keep this in mind: when you change something, then notice something you hadn't noticed before, suspect the change you just made as the cause. Should be easy to verify.
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Post by Lefty on Oct 25, 2012 8:08:32 GMT -7
Is a bad filter cap hard to replace? The amp is only 8 months old so I'm going to be really disappointed if it's something other than a tube. Thanks for the help guys. If it is a cap, I'd have Doc fix it. It requires working around high/stored voltages. +1 on what Steve said.
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Post by DRZ on Oct 25, 2012 13:43:14 GMT -7
Always keep this in mind: when you change something, then notice something you hadn't noticed before, suspect the change you just made as the cause. Should be easy to verify. +10000 Christmas morning DR.Z
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Post by zpilot on Oct 25, 2012 14:31:16 GMT -7
Any reliable tech can replace a cap. If you send it to the Doctor they will also check all the voltages throughout the amp. They will know what the design voltages should be and, from past experience, what else to look for.
If I lived as close as you do I would take it up there myself. I always like doing business face to face.
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Post by bluzman on Oct 25, 2012 16:29:00 GMT -7
Always keep this in mind: when you change something, then notice something you hadn't noticed before, suspect the change you just made as the cause. Should be easy to verify. I changed the volume know from 9:00 to 3:00 and noticed the amp got very loud and full!
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Post by Matt on Oct 28, 2012 17:03:34 GMT -7
Good news. I luckily had an old set of tubes (that I hung on to for no particular reason) that I threw in the amp and the problem disappeared. So glad it was a tube and not something more.
Thank you to everyone who helped!
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Post by benttop (Steve) on Oct 28, 2012 18:57:44 GMT -7
;D
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