strange sounding Cs

[sdorer]

Friends,
I built an 5E3 circuit and it's working fine however when I play a C (single note) on the guitar the note breaks up and rumbles shortly into the note. This doesn't happen with B or C# but only on C. Also it happens on any two different octaves an any string playing these pitches. Also it doesn't happen if these notes are played softly but does when the attack is harder. Any thoughts?

[greiswig]

Not to be a jerk, but in case you haven't yet...

Check the string and the guitar first.

[Phil_S]

Change your power tubes. If it stops, it's the tubes. If it doesn't I'd look for a cap or resistor that vibrates or isn't firmly "seated" with a bit of tension on it's leads, but not too much tension. If nothing is loose, maybe it's a bad filter cap.

I have a pair of tubes that are good for a buzz on the low A. I keep them around as a scrap pair for testing. They buzz in every amp I try them in.

[Structo]

Sounds like it is frequency dependent.

I would check for sympathetic vibrations on the chassis, cabinet, etc for loose screws, bolts, faceplates, etc.

[Firestorm]

sdorer -- how closely did you follow the original layout? That's the amp Gerald Weber used to talk a lot about. On many of them, the .1 uF cap from the PI plate supposedly parasitically couples to the input and makes all sorts of strange sounds.

[sdorer]

Thanks for the input I will give these things a try. No offense taken regarding the guitar. It has the same symptoms with different instruments however.

[passfan]

Same thing happened to me with a 5E3 build. It went away when I separated the chassis from the speaker cabinet. Turns out it was a mechanical vibration.