Blown Transformer?

Brian Kingsbury · 20th February 2010, 08:37 PM

I built an F5 several months ago and have been listening happily to it for some time. There was a 60hz hum from a poor arrangement of the grounding. I opened her up and rewired the grounding scheme to seperate the signal and power grounds. When I plugged it back in, everything sounded much better, hum was gone but after a couple of days the amp just stopped working.

I opened her up again and starting checking voltages. Fuse isn't blown and there's 120 volts on the xformer primaries. The secondaries still connected to the rectifiers measured .15v. Disconnected (no load) one secondary measures 86v and the other is 66v.

I'm using an Antek 18v 600va transformer and was wondering what might have gone wrong and wether I should just order a new one or if this one is somehow salvagable.

eyoung · 20th February 2010, 11:59 PM

What are the AC values in on the rectifier bridge and the dc values out on the bridge with nothing hooked up to it???

Regards, Elwood

Brian Kingsbury · 21st February 2010, 06:28 AM

I can't measure that since I've taken the transformer out of the amp. Since it's clearly faulty I don't want to risk damaging other components. After pulling it out of the case and plugging it into 120v AC I got 90v AC on the secondaries. I really don't know what could have gone wrong to change the output voltage so drastically.. There's infinite resistance measured across primary to secondary so there's not a short and everything physically looks normal. It's still wrapped up nicely and hasn't been touched since it was installed.

Brian Kingsbury · 21st February 2010, 04:30 PM

John Ango from AnTek got back to me this morning and recommended I check the fuse. It was blown but had a tiny bit of connection still. It had just enough material connected that it was getting the 120v from the wall to the tranformer but almost no current was getting through.

In retrespect, I probably should have checked the fuse first but the amp had a somewhat 'slow death' and had played poorly for a while before dying off. The fact that it still had voltage on the primaries made me assume the fuse was good. Lesson learned.

20th February 2010, 08:37 PM	#1
Brian Kingsbury diyAudio Member Join Date: Aug 2009 Location: San Diego, CA	Blown Transformer? I built an F5 several months ago and have been listening happily to it for some time. There was a 60hz hum from a poor arrangement of the grounding. I opened her up and rewired the grounding scheme to seperate the signal and power grounds. When I plugged it back in, everything sounded much better, hum was gone but after a couple of days the amp just stopped working. I opened her up again and starting checking voltages. Fuse isn't blown and there's 120 volts on the xformer primaries. The secondaries still connected to the rectifiers measured .15v. Disconnected (no load) one secondary measures 86v and the other is 66v. I'm using an Antek 18v 600va transformer and was wondering what might have gone wrong and wether I should just order a new one or if this one is somehow salvagable.

20th February 2010, 11:59 PM	#2
eyoung diyAudio Member Join Date: Aug 2007 Location: Sunny SC,USA 15 min south of Charlotte NC	What are the AC values in on the rectifier bridge and the dc values out on the bridge with nothing hooked up to it??? Regards, Elwood __________________ "when you open your mind to the imposible, soon you will find the truth...."

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21st February 2010, 06:28 AM	#3
Brian Kingsbury diyAudio Member Join Date: Aug 2009 Location: San Diego, CA	I can't measure that since I've taken the transformer out of the amp. Since it's clearly faulty I don't want to risk damaging other components. After pulling it out of the case and plugging it into 120v AC I got 90v AC on the secondaries. I really don't know what could have gone wrong to change the output voltage so drastically.. There's infinite resistance measured across primary to secondary so there's not a short and everything physically looks normal. It's still wrapped up nicely and hasn't been touched since it was installed.

21st February 2010, 04:30 PM	#4
Brian Kingsbury diyAudio Member Join Date: Aug 2009 Location: San Diego, CA	John Ango from AnTek got back to me this morning and recommended I check the fuse. It was blown but had a tiny bit of connection still. It had just enough material connected that it was getting the 120v from the wall to the tranformer but almost no current was getting through. In retrespect, I probably should have checked the fuse first but the amp had a somewhat 'slow death' and had played poorly for a while before dying off. The fact that it still had voltage on the primaries made me assume the fuse was good. Lesson learned.

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