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DAM Broken tube?

When putting the KT90 output tubes in my new Rogue Cronus Magnum, I heard something rattling around in one of them. The other three are quiet. Does that mean the tube is definitely bad and I should not power the amp up?

I wanted to have it up and running in a couple hours.

When I picked it up at UPS, they had the box standing on it's side despite arrows on the box showing it should be laid flat and fragile symbols. When I pointed it out they said "Oh we don't do that", referring to following handling instructions on boxes.
bajaed
chuck
209 posts
 
Bajaed,

sometimes pieces of glass break in the the tubes. It does not mean that the tube is definitely bad. Do you see any physical damage to the tube structure? If you have access to a tube tester I would check it for shorts.
mofimadness's avatar
mofimadness
5,141 posts
 
I had that same thing happen a couple of times. The tubes worked just fine each time. It could just a loose piece of wire or structure that will rebond once it gets hot enough.
rodman99999
6,206 posts
 
Have it tested for shorts, before installing and powering up. Generally; there will be no problem. I would hate to use my power amp as a tester though. A shorted tube could get ugly, in your output stage.
bifwynne
2,206 posts
 
Agree with Rodman. I just lost a bias resister because a tube went bad. Fortunately, the factory arranged for same day service at my home, all under warranty. When trying out the socket with a back up tube, one of the back up tubes also had a rattling sound. Both tubes went back to the vendor for replacement. Trust me, you don't want to use the amp as a tube tester.

Further, no one can diagnose a tube problem without seeing the suspect tube, and even if the tube is directly examined, I still wonder. Good luck.
jallen
502 posts
 
The rattle is one source of microphonics...likely a loose part, not necessarily a bad tube. A tube tester is a good thing, but does not tell all. jallen
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