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?
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?
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.
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.
Talent hits a target no one else can hit; Genius hits a target no one else can see. - Arthur Schopenhauer
The important thing is not to stop questioning. - Albert Einstein
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