Edcor XPWR005 issues

sweet & juicy SE amp for 1626 Darlings and the 6L6 family

Edcor XPWR005 issues

Postby ekubota » Sun Feb 15, 2015 3:57 pm

I finished my Clementine 6L6 Ultra about a week ago, and from the first power-on it worked perfectly, with the power transformer never getting more than slightly warm.

On Friday, however, the music suddenly faded and died during a listening session. The 1.5A slow-blow fuse had blown, and the power transformer was noticeably warm (and emitting a solvent or ozone-type smell), but no other components appeared hot or damaged. Further, I checked the entire circuit and no wires or components were improperly installed or shorted to ground, and all resistance specs (including for the components in the power section) are normal.

To help isolate the problem I removed the power transformer from the amp and tested its DC resistance: 2.5 ohms across the primary, around 82 ohms across the main secondary (62 ohms from one red wire to center tap, and 20 ohms from the other red wire to center tap), and around 0.4 ohms across the heater secondary. The differential between the two sides of the main secondary made me suspect something was wrong with the transformer. Then I briefly applied 120V AC, and the transformer immediately started buzzing/arcing, and the solvent/ozone smell returned.

Given the above, I believe the power transformer is defective. What I am struggling to understand is why it functioned normally for about a week before failing. Again, I've thoroughly checked all other aspects of the amp and everything else appears fine. Also, as I noted, the failure occurred suddenly in the middle of a listening session--there was no external physical stimulus, or any visible symptom like smoke, etc.

Has anyone experienced a similar issue? I also plan to contact Edcor on Tuesday to get their thoughts. Thanks.
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Re: Edcor XPWR005 issues

Postby Geek » Sun Feb 15, 2015 7:37 pm

The ozone smell is a sign of insulation breakdown. I'd call Edcor for a replacement.
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Re: Edcor XPWR005 issues

Postby ekubota » Tue Feb 17, 2015 2:39 pm

Update: in case it's helpful to anyone else who ordered recently, Edcor said my PT was part of a batch with some kind of defect related to the secondaries. They are sending a replacement.
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Re: Edcor XPWR005 issues

Postby Ludwig » Wed Feb 18, 2015 2:03 pm

You got a better response than me. Mine didn't fail, but it buzzed like a helicopter and they simply said that it was getting too hard for the to keep up with all the primary voltages around the world!
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Re: Edcor XPWR005 issues

Postby Shannon Parks » Thu Feb 19, 2015 5:44 pm

Check that your rectifiers are both OK with the diode function on your DMM while you are waiting for a replacement PT. Glad the fuse did its job!

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Re: Edcor XPWR005 issues

Postby ekubota » Thu Feb 19, 2015 10:08 pm

Thanks, yes. They test as normal but I will probably replace both as a precaution.
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Re: Edcor XPWR005 issues

Postby Geek » Fri Feb 20, 2015 4:25 am

I've had fast recovery types fail, yet still test good (???)

An example is some UF4007 that went *POOF!* - they passed the DMM diode test, but still popped fuses in the circuit. Putting them on a DIY zener checker (makes a low current 0-150V ramp) showed they rectified below 20V or so (hence passing the diode test), but broke down above that and turned into a really loose tolerance varistor =:o

A good tidbit for the technician's experience box ;)
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Re: Edcor XPWR005 issues

Postby Shannon Parks » Fri Feb 20, 2015 7:35 am

Geek wrote:I've had fast recovery types fail, yet still test good (???)


But did the forward voltage drop seem suspicious? Or possibly the two values were strangely different? Don't scare me like this. ;)

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Re: Edcor XPWR005 issues

Postby Geek » Fri Feb 20, 2015 12:47 pm

Prepare for a horror picture, Shannon =:o

The Vfwd wasn't unusual.... I remember it being a little lower, but not enough to cause suspicion.

Cheers!
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