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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
rrog
1,958 posts
 
Jea48, Regarding your comment "(Dumb way to build something)". The output transformer case may be grounded. Most people use terminated speaker cables eliminating this problem.

Also, powering up a tube amplifier with no load is very hard on output tubes and stresses the amplifier. Youtube is good for some things, but apparently not for biasing tubes.
hifigeek1
770 posts
 
Normally, when I bias a tube amp, unless the manufacturer says to have a load on the output, I don't. I do however, have shorting plugs for the single ended inputs. That way I know there is no signal going through the amp while I am biasing it and therefore not driving a signal through an unloaded output transformer.
truemaineiac's avatar
truemaineiac
249 posts
 
I would be very sure that the amp is connected properly to the pre-amp and the amp is configured properly for that input. As well, make sure that the speakers are properly connected as well.

It is interesting that you have never had the amp working properly so it is not so straightforward to blame the biasing exercise on this. I would contact the manufacturer for assistance.
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banquo363
371 posts
 
yes: check the fuse(s)
bombaywalla's avatar
bombaywalla
1,958 posts
 
Vu001,
it's a bad idea to turn on a tube amp without a speaker load since tube amps always have a power output transformer where the primary winding is connected to the output tubes & the secondary winding is connected to the speaker binding posts & expecting a speaker to be connected. If not connected to a speaker, there is a high probability that the tuned circuit connected to the secondary of the output transformer can start oscillating & destroy itself.

Additionally, this cut & Pasted from David Berning's website:
Audio-output transformer-coupled amplifiers should not be operated without a load connected because the inductance of the transformer's primary can cause the plate voltage to reach a sufficiently high voltage to break down insulating materials, resulting in amplifier failure and even fire. Some amplifiers are even unstable without a load.
I used to own a Jolida & AES Six Pac tube amps & even tho' Cary said it did not matter whether or not there was a speaker connected I always made sure that a speaker load was present during biasing.
Some info for you to read:

http://www.hometheater.com/content/amplifier-damage
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