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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
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
3,969 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.
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almarg's avatar
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almarg
9,670 posts
 
I can't say from the facts stated whether or not the output transformers are blown, or if something else could be causing the problem. However, I would make two points:

1)Whether or not damage will result from powering up a tube amp (that has output transformers) and subsequently powering it down without having anything connected to the inputs and outputs depends on many aspects of the design of the amp. Experience with a different model amp has no relevance.

2)Regardless of whether or not damage might result with a particular amp design, IMO doing that is ALWAYS bad practice, especially if shorting plugs are not used on the inputs. In addition to the possibilities that have been stated, turn-on or turn-off transients could in effect put a signal through the amp. That is particularly likely to occur when the amp is being turned off, if shorting plugs are not connected to the inputs. Transients generated at the instant the power switch opens could couple into the inputs of the amp (to a greater extent than they normally would, because of the high impedance that is present at that point when the inputs are unconnected), then be amplified through the amp's signal path, resulting in huge voltage transients being caused by inductive kickback in the unloaded output transformers (as described in the paper Jim provided).

How likely is that to occur and cause damage with any given amp design? Who knows? But IMO it is a risk that there no point in taking.

Regards,
-- Al
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