There's a baby with a harmonica inside my amp.

[Gaz]

Anyone ever heard this noise coming out of their amp on certain notes? In my case, when I hit single notes in the 'middle register' of the guitar (i.e. 7th fret on the G string) I hear the sound of baby's 'waaaah' or harmonica after the note stops. The noise is being amplified through the speakers, and not just comingn from the head itself.

Last time at practice I thought it was a vibration being caused by the cab, so i put a piece of sound treatment foam between the head and cab to no avail. I should've just put in on the floor to make sure.

I have this idea that it's one of the 12AX7 shields vibrating against one of the tubes and being amplified, but I can't trouble shoot it until next week.

Blah, blah, just wondering if anyone has experienced this? I kinda like it... just not for recording.

[drewl]

Sounds like a microphonic tube.
Try tapping on them with a pencil or something to see which one(s) make noise.

[Gaz]

They all make some noise when they're tapped on, but that's because it's a high gain 60 watt amp. I've had a microphonic 12AX7 in V1 before that caused a very annoying unstoppable feedback, but this sound is very different - lower in pitch than feedback.

Could a microphonic tube cause the noise I described as well?

Thanks.

[rockon1]

Rule out the speaker and try a different cab. Bob

[Gaz]

Yeah, already tried another cab, same problem. Thanks.

[rockon1]

I would look into the the tubes then. Ive had 12AX7's with "rattle" - not the same as microphonics. The inards actually vibrate causing strange noises-usually old stock tubes though. Bob

[Gaz]

I've got a Sylvania 12AX7 D-Getter in there now, so I'll try and swap it out. Thanks, sounds like that just might be the ticket.

[rockon1]

I've got a Sylvania 12AX7 D-Getter in there now, so I'll try and swap it out. Thanks, sounds like that just might be the ticket.

Let us know if thats it. Ive run across rattle too many times with my old stock 12AX7 collection unfortunately. : > ( Of coarse with over 1000 old stock 12AX7's I guess thats not too unexpected. Bob

[Gaz]

will do...

[Gtr_tech]

Power tubes can rattle too so rap on them a little and see if they cause any noises. You may have cracked solder somewhere causing vibration induced weirdness. Dirty/loose tube socket(s), cap going south....could be anything really....

[Gaz]

I've been taking the PT in and out a lot lately, so I very well may have shaken something lose in there. I'll check the joints too, but man I don't want to deal with replacing wacky Russian caps