2. amps-preamps
  3. 1309723649

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
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
rrog
1,958 posts
 
I have had many power tubes rattle and never had a problem.
More to discover