Crate V15 ringing/rattling noise...

[bagelwithin]

Hey guys. I'm playing through a Crate V15 tube amp. Recently retubed (new speaker installed about 3 years ago). A few months ago it started making a ringing/rattling noise in certain frequencies (Bm chord @ 7th fret). I changed the power tubes at that point and the noise went away. I noticed it started making the noise again and changed the pre amp tubes, which seemed to make it worse. I put in brand new tubes. I had been working with an amp tech who tightened EVERYTHING, replaced screws and various parts to ensure that nothing was loose and rattling around inside. To me, it sounds like a tube thing. It sounds like something inside one of the tubes is rattling around. The tubes are also extremely close to the speaker...would this affect that? I don't understand how three brand new pre amp tubes could make this happen. I suppose it's possible that I got a bad tube?

Has anyone had a similar issue with a small combo amp? I have no idea what to do. Any help would be appreciated.

[Enzo]

Noise and buzz from a combo? yes, that would be pretty common.

With the amp running, go in back and tink on each tube with your fingernail, or a pencil or a chopstick. Do any of them make a noise come out the speaker? Is the nature of that sound similar at all to the nature of your mystery noise?

Have someone play through the amp so as to make it do it a lot, wwhile you watch in back, Now firmly grasp each tube, one at a time, going down the row. Use a rag or a glove if they are too hot for you. Does grasping a tube make the noise stop?

Tubes can become microphonic - sensitive to vibration. Tubes can become mechanically loose inside and rattle around inside their own glass. Those tests expose that.

[Chuck H]

+1
And I'll add one more test. Plug the amp into an external speaker. Did the problem get better? If yes then you have a vibration related problem. Most likely a tube or tubes. But... Now plug another amp into your Crates cabinet. Do you hear the rattling? If yes then you have a construction related mechanical noise to hunt down. Mechanical noises can be very good at imitating electronic noises.

[bagelwithin]

Thanks guys, very helpful. I forgot to mention that we did plug in an external cab and the running ceased. I'm fairly sure the speaker is in good shape. The three pre amp tubes have those metal casings over them. Could those be a cause? I will try the tests this afternoon and get back to you. Thanks again.

[Enzo]

The tube shields usually are not buzzers, but pull them off and see.

[Chuck H]

I forgot to mention that we did plug in an external cab and the running ceased.

I don't know what this means or how to relate it to the process.

[g1]

Appears to be a typo Chuck, running = ringing.

[Gtr_tech]

EL84s aren't the most mechanically robust tube out there to begin with. Stick 'em in a combo close to a speaker and don't expect 'em to last long. Plus....that particular amp's cabinet is pretty cheesy and actually vibrates with the speaker. So it makes the tubes get ate up that much faster.

EL84's = have some spares on hand at all times....