2. amps-preamps
  3. 1333676636

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
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
Post removed 
wilsynet's avatar
wilsynet
264 posts
 
It now needs to be repaired. Looks like its time to either send it to the manufacturer or to a repair shop for diagnosis.
ebm
9,311 posts
 
Your in a world of hurt!!
larryi
4,057 posts
 
It is not that likely that having no speakers connected accounts for your problem. That could overload the primary side of the output transformer, but, that usually happens when there is an input and the amp is supposedly putting out a lot of power, except, there is no load attached. If you had no signal going to the input, I don't think you caused the problem.

Perhaps an output tube was bad (shorted) and that caused the main fuse to blow. Check all fuses first; if you are lucky it is just the fuse.
More to discover