How to determine faults

[txstrat]

Hi all,

in case a output transformer was blown. How could I determine why it has burned up. I mean is there a way to find out if there was no speakers connected or the tubes took it down with them?

[MWJB]

Either scenario would cause a short in the primary, so in the case of an OT going down I would double check speaker condition, ohmage, speaker wire, jack contact etc., then see what sort of idle plate current the OT was faced with, check for shorts at tube socket pins etc. Be aware that maunfacturers often used undersized OTs, in these cases OT failure might be considered "normal".

If there is no obvious cause, other than you might suspect the OT was not really up to the job, then it would make sense to upgrade to one that could handle higher currents.

[txstrat]

If there is no obvious cause,...

What if I suspect somebody tried to play the amp with no speakers connected, how could I tell the OT burned up because of this. I don't have this scenario goin down here, I'm just interrested if there's a way to find out.

[MWJB]

Truth serum, polygraph, waterboarding, CCTV? :-)

No, there is only really your judgement - even normally honest people can lie if they think the truth is going to cost them money.

[Enzo]

The only way you'd have any idea is to perform an autopsy. if you disassembled the thing and carefully unwound the windings and watched for signs of an arc between layers or between winding turns or from a turn to the frame, you could find out if it arced. You still don;t know if it was because someone ran it unloaded or if it failed for some other reason. SOme volatge spike could have happened.

If the windings are discoloerd, signs of heat, well maybe some tube failure caused excess current to flow a long time. Especially if the thing was over fused.

But really, to me it is like getting a flat tire on the highway. You COULD walk back a half mile to see if you can spot what did your tire in. Or you could just mount your spare, go get a new tire, and get on with your life.

[txstrat]

Enzo
I really DO like your comparisons with the car. It makes things quite clear.
Thanks to both of you for sharing your thoughts.

[Enzo]

Oddly enough, I have a flat tire this morning. Gotta deal with that on the way home.