New Variac for Joule Electra Amps

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)?

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.

That is where you call in a qualified tech.

Why does it take 10 weeks?? Joule's website sites an average turnaround time of 6 business days with the longest being 15 days.

Outlier,

For what the Joule Electra VZN-160 amps retailed for new I would buy the variac the manufacture recommends from the manufacture. From your last post there is a lot more going on than just varying the voltage to the amps. It sounds like the variac is built/mated specifically for the amps.

I would suggest when you get the new one keep a log on the hours used. Check the autotransformer winding wiper brush for wear and have it replaced long before it’s end of life.
I also hope your amps were not damaged when the variac started arcing.

Best of luck,
Jim

Outlier,

For what it's worth had the 120V branch circuit that feeds the variac been protected by an AFCI,(Arc Fault Circuit Interrupter), breaker the breaker would have tripped open when the variac started series arcing. I am just not sure if under normal operation of the variac a slight arcing of the wiper brush contacting the bared autotransformer coil as the variac was ramped up or down might cause the AFCI breaker to trip open.

You could have an electrician install an AFCI breaker in the electrical panel that feeds the branch circuit and find out when you get the new variac.

Note, depending how old the electrical panel is and manufacture of will determine if the electrical panel manufactured breaker will fit the model/style/series of your panel.

AFCI breakers have been in use since 1999. As per the 2014 NEC code all newly installed 120V 15 and 20 amp branch circuits used for lighting and receptacles in habitable areas of a residential dwelling unit shall be AFCI protected. It should be said the AHJ, (Authority Having Jurisdiction), has the final say where they must be used.

http://www.afcisafety.org/qa.html
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Jea- Yes this a purpose-built variac on the Joule amps. Given the heat load that 16 of those 6cc3b tubes put out, there must be a $hitload of juice (that's as technical as I get) of current or voltage or whatever being dissipated by those amps to be able to put out 160 wpc so I would be very cautious about using anything other than Joule-supplied variac.

Outlier- FWIW, did you follow Jud's directions as far as slowly ramping up voltage when you powered up the amps?

Disclaimer- I owned a VZN-80 for several years. Other than that, I have no technical or engineering skills. Bit I did stay at a Holiday Inn ;-).