Rattling sound in power tubes

[überfuzz]

I have a quad of 6L6 of which one makes a rattling sound at certain frequencies. Is there a any way to dampen this? The set of tubes have a über nice sound and it would be great to be able to use them.

[Chuck H]

You could limit their use to head type amps and not place the head atop the cabinet. Other than that I would say that a microphonic tube is either old, bad or a cheap Chinese tube. However you slice it's either limited in usefulness or on borrowed time.

[überfuzz]

Darnit! The bulb seems to be somewhat lose. As a last resort I'll glue it with heat resilient silicone.

[psychbeat]

what about those rubber/plastic rings audiophile guys use?
or marshall type springs or both?
epoxy might help too but will look ugly

[km6xz]

Glue with a firm setting glue, a vibrating envelope will fatigue and eventually break the wire lead embedded in the bottom of the envelope, particularly if used in a combo that is subject to a great deal of vibration.

[überfuzz]

It seems I jumped to conclusions. The bulb is firmly attached to the tube socket. I dismounted al power tubes and examined them.

I also decided to open the amp up to poke around a bit, get some readings, strap some wires etc. When I was done disaster struck. I dropped the damn thing on the floor, a free fall of maybe 60cm. (I didn't place the cabinet on the working bench due to the weight of the amp.) Imagen my gut right after... Before I lifted it up I remember thinking, strange that there's no broken glass. Divine intervention - Only think broke was the tube shield of V1 and a mini dent on the PT.

Oh, there's one more thing. My multimeter broke the fall, I wont go into any disgusting details. My precious multimeter, let's just say it's retired. Ah well...

[Chuck H]

If it hit hard enough to dent a transformer that could be bad. Transformers don't like to be hit that hard. You'll want to take voltage readings when you get it back up and running. Tall order with no meter though.

[überfuzz]

Well, as you probably can imagine I was rather nervous about the PT when I saw the dent. Beside actually testing/playing the amp I did some probing. I couldn't find and odd numbers...

The dent is on the pan like bottom of the PT and it's quite small. It's one of those with a horizontal iron with a vertical coil. My guess is that it didn't affect or even touch the coil inside.

Edit, I have one meter that's still in the game. It's crap but still...