Power Surge: Power Transformer damage?

[rockybottom16]

A friend was using an amp I built and the venue had some electrical problems that took out every amp fuse on the stage. Being told that the wiring problem was fixed, amp fuses were replaced and the show went on. Unfortunately, my friend only had a 10 amp fuse (he says he thought it was labeled 1 amp). Then the venue's power went haywire again and naturally my friend's amp spewed a cloud of white smoke and stopped working.

I have the amp on my bench now. The first filter cap boiled over, but that's the only visible evidence I see. Neither transformer smells of smoke. Should I assume that the power transformer might be compromised as well? He uses this amp a lot, and if there's a chance that it has been damaged at all, I'd like to replace it. I also plan on replacing the power tubes and all the filter caps.

Is there a reliable test to check the P.T. for any damage? It's a Hammond 270FX. The amp is a 36 Watt Lite type with 4 - EL84's.

Thanks in advance for your input!

[xtian]

Just pretend this is a new build, and follow first time startup procedures. Remove tubes, use bulb limiter, check voltages, etc.

[Enzo]

I would assume the transformer was good unless I had evidence to the contrary. I never assume a transformer is bad, because they are the most reliable parts in an amp.

If your friend plays gig often where power could be an issue, have him consider a power conditioner (not just filter). In my old country house, I used a Tripp Lite power conditioner for my computers for years, it kept a constant mains voltage through many power glitches.

[Mick Bailey]

Hammond transformers are pretty good and will withstand a fair bit of abuse. If the overload was bad enough I would expect the HT secondary winding to fail. Generally, a momentary overload won't affect the transformer. The situation is no different to what I see with amps that have a shorted tube and a ridiculous HT fuse fitted (one recently came in with a 15A HT fuse instead of 1A) Did the 10A fuse blow?

Plenty of faults stress transformers and many amps don't have a HT fuse. I always do a visual check of the transformer and the sniff test, but rarely is there any need to replace the transformer unless there's obvious damage. If the secondary voltages are OK I wouldn't worry.

[TimmyP1955]

Be sure to have him present your bill to the venue.