AudiogoN Forums: Did I blow my tube amp?

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 (Threads | Answers | This Thread)

04-05-12

Responses (1-24 of 24)

Click title to read one, or click date to read all below it.

04-06-12 not sure why the guy did that...... manual does not say to d ... Jea48

04-06-12 Did you check the b+ fuse? when i changed the power tubes i ... Ncarv

04-06-12 I am no expert in the matter but my cary amps are biased wit ... Dilly

04-06-12 It is my understanding that you never under any circumstance ... Markwatkiss

04-07-12 Thanks guys for the inputs so far. i must add that the amp i ... Vu001

04-07-12 Purposely withholding the name and model of the amp will not ... Onhwy61

04-06-12 Hi all ! the vtl amp i had said to connect the speakers for ... Bradluke0

04-07-12 Jea48, regarding your comment "(dumb way to build somet ... Rrog

04-07-12 Normally, when i bias a tube amp, unless the manufacturer sa ... Hifigeek1

04-07-12 I would be very sure that the amp is connected properly to t ... Truemaineiac

04-07-12 Yes: check the fuse(s) Banquo363

04-07-12 Vu001, it's a bad idea to turn on a tube amp without a speak ... Bombaywalla

04-07-12 rrog, i was only repeating the info from the user manual o ... Jea48

04-07-12 It now needs to be repaired. looks like its time to either ... Wilsynet

04-08-12 Your in a world of hurt!! Ebm

04-09-12 It is not that likely that having no speakers connected acco ... Larryi

04-10-12 i ran across an interesting white paper by hartley peave ... Jea48

04-10-12: Almarg
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
Almarg (System | Threads | Answers | This Thread)

04-10-12 Though i have never powered up a tube amp without the speak ... Jea48

04-11-12 I have, on several occasions, turned on my amps and noticed ... Larryi

04-12-12 Things to check: 1 -do the tubes still light up? if not, c ... Dividebytube

04-13-12 It would be great to know what the outcome of this is. Truemaineiac

04-21-12 So after taking the amp to an experienced tube technician, t ... Vu001

04-21-12 Also the thing to remember is, no one ever sells an amp with ... Hifigeek1