New Variac for Joule Electra Amps

Outlier,

Sounds like you slowly ramp up the variac with the amps connected, powered on, and then set the desired voltage under load. This action over time will cause wear on the brush that contacts the autotransformer winding directly proportional to the connected load of the Joule Electra amps.

First I would not try to use the variac until you have it checked out. It could be something as simple as a fuse holder as Thaluza stated in his post. Or maybe even a loose connection. Or it could be more serious like a bad brush on the dial slider arm that contacts the winding of the autotransformer. If that is the case hopefully the autotransformer winding is not damaged.

If you are the least bit mechanically inclined you could pull the cover from the variac and have a look inside.... Make sure the variac is unplugged from the mains AC power before you start.... You could then see where the problem is. Look for a burned spot that will more than likely show signs of black carbon and will have a burnt smell.

Here is a nice video I found doing a Google search.

https://www.youtube.com/watch?v=M8cJrJyR87o
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Jim

Thanks guys for the input. I'm not so mechanically inclined, but am ambitious enough to try.

The variac used to have the original (small) fuse holder scenario, and the fuse kept failing on me, so I sent it back to Joule and they replaced it with a massive essentially external (sticking out) fuse assembly which has since been bullet proof, so I don't think it's the fuse in this case. Just to be sure, I had swapped out a new fuse just to see if there was any change in operation and the sparking, glowing and burning symptoms were still there.

I'll see if I can investigate further

I managed to open the variac and I saw that the windings were blackened generally, there was little to any 'brush' to speak of and probably most worrying, there was a vertical segment of the winding that was essentially gone (the outer metal winding was likely smoke/carbon at this point, revealing an inner winding. I guess it's hard to describe but I have the photo.

I wish I could just buy a cheap new one or have this one fixed quickly, but am guessing there's no recourse there?

I guess I'll have to bite the bullet and ship it to the after-warranty service dept.

Outlier,

It's toast! It is not worth repairing in my opinion. I would just see what a new one would cost. A new one will come with a warranty.

The variac is the latter; manually 'dialed up' to operating voltage of approximately 166 volts.
12-09-14: Outlier

166 volts? Why so high? Does the power amps have a regular US 15 amp 125V plug on the end of the cord?

You can buy variacs all day long that go up to 140V that plug into 120V mains power.

Somewhere on the variac should be a data plate showing the input voltage and the FLA, full load ampere rating of the unit. It should also list the max output voltage.

Here is one manufacture I found using google.
http://variac.com/staco_3pn10_20.htm

Scroll down the page to Portable Voltage Doublers - 120V input/0-280V output.

http://www.iseincstore.com/3pn2520b-xdamvariabletransformer120vacsinglephaseinput0-280vacoutput43acasedmodelwithcordplugreceptaclelightedswitchandfu.aspx

Note the 250 volt output receptacle.
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Hi Jea48,
Thanks for the great info. Yes, I'd feel far comfortable buying a new one, assuming it will work with the amps.

The 166volts recommended setting is likely because the momoblock amps are approximately 160 watts per channel into 8 ohms and the variac is driving both of them (Could that be it? - The setting recommendation is quite specific in the instruction manual). A friend of mine had the VZN-80 (which is essentially the stereo version, but half the power - like one monoblock with two sets of speaker outputs in inputs) and the voltage setting for his variac was essentially half mine.

My wall outlets are regular 15-amp.

I think a key reason an aftermarket variac may not work though is that the one that came with the Joule connects between each amp twice (an output power cable from the variac to the amp, and back from the amp to the variac, for each channel). Two of those connections are hard-wired from the variac and plug into the amp, and the other two connections are regular/removable power cords (plugging into the variac via male connection and into the amps via female connection, if that makes sense). I'm not sure why that 'feedback' loop is there...and I don't think other aftermarket variacs have that setup.

If it's useful I could send photos..

Thanks again for the great help. I certainly would feel more comfortable with a new variac, but would it work with the amps (especially given what I assume is some 'feedback cabling' that is employed with the Joule amps)?