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Did I blow my tube amp?

So here's the story: I recently received my tube amp and replaced the power tubes. So naturally, I wanted to bias them to make sure they work properly. I've never done any biasing before and checked some youtube videos on biasing. One of the youtube video had a Manley Stingray connected to power, no input signal, and NO speakers connected. I did the same. After the biasing is done, I connected the speakers and input signal, but for some reason so sound came out.

So the question is: did I blow my output transformer? Simply by not connecting the speakers while biasing or just having the amp on for a short while? From what I have read, it should be ok to have no speakers connected as long as there's no input signal.

I had another tube amp before this, and turned it on one time without speakers connected and it worked flawlessly after.

Could you guys shed some knowledge or personal experience on this topic?
vu001
larryi
4,093 posts
 
I have, on several occasions, turned on my amps and noticed that one channel was not working because a spade has worked itself loose. Nothing has ever happened.

I never start a listening session with the preamp turned up very much, so I do not subject the amp to high level output into such a no load situation. I know it is not a good thing to do, but, I have never, nor has anyone I know, experienced damage from operating without a load attached.
dividebytube
50 posts
 
Things to check:

1 -Do the tubes still light up? If not, check the fuse.

2 - Check connections - both input and output. We all do silly stuff, like the time I plugged the speaker wires in to the 4-ohm and 8-ohm tap, hence no sound!

3) if you have the amp on - with the speakers plugged in - do you still get a bias reading? If so, that indicates that power is reaching the tubes.

4) I've been messing with tube amps for over 20 years and have never, ever blown an output transformer. There may be something else that went bad inside. If you don't have experience working with high voltage, then have a tech take a look for anything obvious. Luckily most tube amps are fairly easy to troubleshoot.
truemaineiac's avatar
truemaineiac
249 posts
 
It would be great to know what the outcome of this is.
vu001 OP
3 posts
 
So after taking the amp to an experienced tube technician, the problem was that 2 of the output tubes went bad, and took out a fuse and fried 4 resistors. On the outside, everything seemed normal since the amp turns on and all tubes light up as usual, but the 2 dying tubes were causing problems behind the scene.

I had a feeling those 2 tubes were going bad and bought replacements, but before I could bias the new tubes, the main fuse blew, cutting off all outputs, causing me to think my biasing procedure damaged the amp.

The amp is now fixed and working better than before. A few things I learned from this experience. If you buy a tube amp second hand, always re-bias the tubes right away even if the previous owner told you he already did. It IS actually safe to bias your tubes without speakers connected on the condition that no inputs is connected either.
hifigeek1
770 posts
 
Also the thing to remember is, no one ever sells an amp with new output tubes in it. I always tell my customers to expect to need a partial or full re-tube when they bring in a used amp to have it checked out.
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