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?
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?
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- 24 posts total
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 |
Though I have never powered up a tube amp without the speakers connected this thread has made me think, WHAT IF?.... What if a speaker cable spade come lose because I was changing ICs or what ever? How many here always check the speaker cable terminations before turning on the amp? I read the owners manual for my ARC tube amp cover to cover twice.... No mention whats so ever.... No WARNING.... Nothing about not running the amp without the speakers connected. I know better.... But what if? I am going to give ARC service a call and ask, WHAT IF! Cary Audio. How do you correctly bias a Cary Audio vacuum tube amplifier? |
I have, on several occasions, turned on my amps and noticed that one channel was not working because a spade has worked itself loose. Nothing has ever happened. I never start a listening session with the preamp turned up very much, so I do not subject the amp to high level output into such a no load situation. I know it is not a good thing to do, but, I have never, nor has anyone I know, experienced damage from operating without a load attached. |
Things to check: 1 -Do the tubes still light up? If not, check the fuse. 2 - Check connections - both input and output. We all do silly stuff, like the time I plugged the speaker wires in to the 4-ohm and 8-ohm tap, hence no sound! 3) if you have the amp on - with the speakers plugged in - do you still get a bias reading? If so, that indicates that power is reaching the tubes. 4) I've been messing with tube amps for over 20 years and have never, ever blown an output transformer. There may be something else that went bad inside. If you don't have experience working with high voltage, then have a tech take a look for anything obvious. Luckily most tube amps are fairly easy to troubleshoot. |
- 24 posts total