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
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.
banquo363
371 posts
 
yes: check the fuse(s)
bombaywalla's avatar
bombaywalla
1,957 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
jea48
2,944 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.
04-07-12: Rrog

Rrog,

I was only repeating the info from the user manual of the Stingray of that particular production model.

Here is the full text.

"IMPORTANT: DO NOT LET THE BANANA PLUGS OR SPEAKER CABLE CONNECTORS (TOUCH) THE TRANSFORMER DIRECTLY BEHIND THEM.
This can short out the amplifier and possibly cause damage to the Stingray, besides losing signal."

See page 7 of link below. Diagram is also shown.

http://manleylabs.com/PDF/HIFI_Manuals/Hi-Fi/Stingraymanual32001.pdf

I notice the design flaw was changed on later models.
.
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.
More to discover