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Variac Question

Discussion in 'Shock Brother's DIY Amps' started by liddown, Oct 27, 2020.

  1. liddown

    liddown TDPRI Member Silver Supporter

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    Hello keepers of the magic smoke...

    I have a question, a bit elementary, but you all have the knowledge and experience...

    I have recently added a variac to my collection of tools for my amp builds... I have used it for a few things, but went to use it for an amp start up on a new build that I wanted to bring up slowly... One of the first things I do when testing a new build is to simply make sure that I have the proper ~120 VAC on the power switch. In this case I was starting up a 5F6A build and on the power switch you have the hot from the line AC on one side of the switch and in this case two hot wires for the (ClassicTone) transformer. Simple right, flip the switch and you pass power to the transformer (as the AC commons are hard connected).

    So this was the first time that I was using the variac in this step, as it is a quick test and I move on, and by using I just mean that I had the amp plugged into the variac and the variac set to 120VAC.

    My surprise was to find when I measured from chassis ground to the switch, I found the 120V on the Transformer side of the switch with the switch off. Yes, everything is wired correctly inside the amp hot to hot, common to common. I guess I could expect this if the hot and common were reversed in a normal outlet (sans variac). But with a three pin grounded outlet built into the variac I should not see the polarity reversed. At least that is what I am looking for confirmation on... I also need to make sure the out the Variac was plugged into was not reversed...

    Am I over thinking this, and there is a simple explanation or is there magic in the variac? IMG_0742.jpeg
     
  2. liddown

    liddown TDPRI Member Silver Supporter

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    Opened up the variac and found that the hot and neutral are reversed... Crap... But an easy fix... Guess when you buy a used item you need to look for past hacking...
     
    jchabalk, sds1 and D'tar like this.
  3. D'tar

    D'tar Friend of Leo's

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    Ha! You already knew the answer! Nice addition to your arsenal. You have a bulb limiter also yes?
     
  4. 82LesPaul

    82LesPaul TDPRI Member

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    D'tar makes a great point. Recommend plugging amp into light bulb limiter and limiter into variac.
     
  5. tubegeek

    tubegeek Friend of Leo's

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    :eek:

    Good save! WTF?!
     
  6. Peegoo

    Peegoo Poster Extraordinaire

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    HO-Lee-Crap! Some goober did some kitchen table elec-chicken work on that thing?

    Glad you found it before you found it the hard way.
     
  7. D'tar

    D'tar Friend of Leo's

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    :lol::lol::lol::lol:
     
  8. D'tar

    D'tar Friend of Leo's

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    The "narrow" terminal/socket should be the line/hot. There have been some power cords that are miswired and causing confusion. Just sayin.
     
  9. Musekatcher

    Musekatcher Friend of Leo's

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    yikes...got bit on an old Peavey with the double ON switch. One direction is ON with a ground, the other is reversed to reduce a ground loop hum..yes, factory feature. I checked the voltage, and was getting 120V to random chassii. I picked up the 120V and got a jolt when holding the strings on my guitar, and brushed another gear's chassis, because I was in my sock feet. Very teachable moment, lesson learned for life. I installed a permanent skull and cross bones on that switch selection, for future victims.
     
  10. liddown

    liddown TDPRI Member Silver Supporter

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    Yup! Sometimes you need to type out your question to discover you own answer...(Sorry)...Never good when you open up something and the first thing you notice is electrical tape :)... And Yes to the light bulb limiter and multiple wattage bulbs to limit different amount of current.. Glad I am not chicken, it would be something most unexpected that will cause the arc! Stay safe!
     
    D'tar likes this.
  11. Pick_n_Strum

    Pick_n_Strum Tele-Meister

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    Good catch. It would've definitely taken me a while to figure out it was the variac that was wired incorrectly!
     
    tubegeek likes this.
  12. jchabalk

    jchabalk Tele-Meister

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    Those plug-in circuit checkers are pretty cheap. i have one i've used on all of my outlets at one time or another, including power strips, variac, UPSs etc. basically any device i want to make sure of i check with that that thing. sure, i can carry my meter around and check but this thing's quick and easy
     
    Pick_n_Strum likes this.
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