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

Showing 2 responses by vu001

Thanks guys for the inputs so far. I must add that the amp I have is not a Manley, I'm just following the steps in the youtube video, which had a Manley Stingray in it (I think it was EveAnna Manley from Manley Labs that did the biasing).

I know that some manufacturers recommend having speakers connected at all times before turning on an amp, but I also know that for Cary amps it don't matter. In my case though, the owner before me had it on once without speakers connected, and it was fine after he passed it on to me.

I checked all connections several times, even swapped in a solid state amp and music played normally at the speakers. I even had experience turning on a Yaqin tube amp before without speakers connected and it was fine after. In my case, there was no input signal connected at the time of the biasing, so there should be no load and the output transformer should be at idle.

The amp still turns on and all tubes lit normally, just no output at the speakers. The tubes usually get really hot when playing, but they seem to be just idling without getting hot. Would a dead fuse cause this?
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.