New Variac for Joule Electra Amps

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 ;-).

Hi Swampwalker, yes, I've been very careful to follow Jud's guidance on dialing up the variac - per his actual words - a smooth, constant motion taking about 5 seconds in total.

The variac is actually very rickety though - my sense is that plenty of aftermarket variacs are bigger and have more tolerance that this one. The core itself is very small compared to some I've seen. I'd love to have one per amp - that would at least half the load, which may be part of the problem with using this little thing to drive both amps.

Outlier- That seems to jibe w my experience w the VZN-80...not the sturdiest construction, that's for sure! Not to denigrate the sound, but no one could Jud of going the 1/2" thick CNC-machined faceplate route ;-)