the life of an AC transformer.........

old transformers never die... they just faraday..

just kidding :)

look up vacuum impregnation of transformers for one.

age+use (a well made transformer on the shelf might last a few hundred years) thermal cycling is probably the biggest factor. overloads and repeated excessive surges (aka lightning) will take their toll. sometimes environmental factors weigh in... excess humidity, corrosive atmosphere, Murphy, even vibration. im sure my list here is not complete.

time to put Mr Bubble in the dumpster and dial up Speedotron for a replacement before you have a fire or inhale poison gasses or something.

Usually they only fail if overheated, sometimes they do delaminate and get noisy but that's harmless other than being annoying.

Assuming it is not being overloaded bubbling yet operational, implies some shorted turns in one of the (usually) hgher voltage windings as they have the higher resistance coils. So, it;s overloaded but still supplies enough voltage to be useable.

Even assuming no abuse through overheating, insulation can dry up and cause problems especially with many tapped coils,

One thing to look at is if the bridge rectifier has RFI suppression capacitors across it. Had a smoking mains transformer caused by one going short circuit (disc ceramic)

--
*Speak softly and carry a cellular phone *

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

I'd guess there is a shorted turn.

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