Plug In Voltage Meter

Discussion in 'Shock Brother's DIY Amps' started by jchabalk, Jul 30, 2019.

  1. jchabalk

    jchabalk Tele-Meister

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    I recently picked up a variac to use with my amps. I just play at home and i've got 6 home built amps - i don't want to unplug and replug my amps all the time so i built a couple of outlet boxes, connect them to the variac and plug my amps into them.

    I'm wondering if there's a plug in voltage meter any of you guys recommend so i can tell at a glance what voltage i'm operating at at the plug - my variac doesn't have one and i've got a couple of extra plugs.

    The dial on the variac is accurate (confirmed with my multi-meter), but that's based on the wall voltage when i checked (it's also difficult to see). I'm interested in the actual voltage without having to test all the time.

    The ones i see on amazon are probably fine, but they're also (probably) junk ;)

    This one is sold under a bunch of brand names, i might just order one and see how it goes but figured i'd check here too.
     
  2. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Why are you using a variac to play your amps through would be my first question?
     
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  3. Milspec

    Milspec Friend of Leo's

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    I bought about 10 of those exact ones off ebay 3 years ago. They all are still in service today and seem pretty accurrate when compared to my multimeter results. I think you can even open them up to calibrate them.
     
  4. Andy B

    Andy B Friend of Leo's Gold Supporter

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    I’ve got two of them. Accurate enough to keep one in my variac to monitor voltage when I’m servicing amps.
     
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  5. BelairPlayer

    BelairPlayer Tele-Afflicted

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    What in the world are you gaining by adding a variac? How does that help you keep from plugging/unplugging?
     
  6. jchabalk

    jchabalk Tele-Meister

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    Mostly it's just another thing to screw around with and keep me from practicing ;)

    The variac has a single plug, i've got 6 amps, if i want to switch which amp i'm playing i've got shut it off, unplug it from the variac, plug in the new one, turn it on etc... What i built is essentially a power strip so i can leave them all plugged in and a couple of them powered on.

    I swear my Princeton sounds "better" though running at 112v rather than the 121 coming out of the wall. With all these different power transformers trying to replication "vintage" voltages and designed to run somewhere between 110 and 120 coming out of the wall the variac lets you manipulate the wall voltage - and as such the b+ and everything else in the amp as well.
     
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  7. jchabalk

    jchabalk Tele-Meister

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    good to know, thanks for the feedback and recommendation. I think a couple of these are in my near future.
     
  8. jchabalk

    jchabalk Tele-Meister

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    It lets you modify the wall voltage to a degree. This is as good a description of what it does as any (link)
     
  9. BelairPlayer

    BelairPlayer Tele-Afflicted

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    I know what a variac is. What I don’t know is why you think you need one.
     
  10. jchabalk

    jchabalk Tele-Meister

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    I mentioned a couple reasons above, 1 cheeky, 1 real-ish.

    I’m mostly trying to understand the audible impact of modifying the wall voltage while playing and overall to figure out a good spot for the voltages in my amps without having to tear them apart and swap components.
     
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  11. jchabalk

    jchabalk Tele-Meister

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    if i’m missing something let me know?
     
  12. BobSmith

    BobSmith Tele-Meister

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    Didn’t Eddie Van Halen use a variac to drop input voltage on his amps early on?
    Someone out their is selling a selectable variac in a box called the BrownBox. Expensive but gets pretty high reviews.

    I like using a Kill A Watt meter because it puts the volt/current meter in line and doesn’t take up an outlet.

    I only use my variac for testing, initial startup and for reforming caps in amps.
     
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  13. jchabalk

    jchabalk Tele-Meister

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    I've heard that too. I've wanted one to use while building and testing too. I'm on building hiatus for a while but am glad to have this for the next time i build too.

    I just dug this up on EVH:

    Edward was adamant about getting his tone through the power tubes and consequently set all volume and tone controls on the Marshall to 10. He controlled the overall volume output in two ways.

    First, he used an Ohmite Variac, a variable transformer that could lower or raise the voltage going into the amplifier (see photo for what a typical Variac looks like). Edward set the variac to approximately 90 volts, thereby reducing the amount of input voltage going to the amplifier (see the Marshall Super Lead article for more information about variacs and attenuators) and allowing the amp to run more reliably. A key element often not considered today when running vintage Marshall amplifiers is that many that were made for export to the U.S. were designed to run at 110 volts and current U.S. outlets run at 120 volts. As a result, while there has been much talk about the dangers of using a variac, in many applications, it obviously serves a benefit.
     
  14. RLee77

    RLee77 Friend of Leo's

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    Sounds perfectly reasonable to me. Variacs are useful for many things, including correcting the line voltage for older amps.
     
  15. Junior Little

    Junior Little Tele-Meister

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    Wouldn't lowering the input voltage also lower the filament voltage? Or, is it not lowered enough to be a concern?
     
  16. jchabalk

    jchabalk Tele-Meister

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    It would. I've got to dig up my amp voltages but i think in most cases the filaments were a little high. I'm also operating under the premise that they can operate a little low too.

    I don't think you can really harm anything by running with lower voltages - except it'll sound like crap at some point. Over-voltage though is another story.
     
  17. robrob

    robrob Poster Extraordinaire Ad Free Member

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    All of my amps run high heater voltage, some are so high I have to run them on a variac or bucking transformer to keep from going over +10%. My wall voltage is often over 125 volts.
     
  18. jchabalk

    jchabalk Tele-Meister

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    How do you handle your variac robrob, do you plug a power strip into it and just power things off/on as needed or do you connect/disconnect them as needed?
     
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  19. jchabalk

    jchabalk Tele-Meister

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    Closing the loop on this.

    I got the meter the other day and had a chance to get it set up today. It was about 2v off what my meter was getting on the circuit so after a couple of adjustments I've got it spot on.

    The blue backlight on it is pretty bright so i plugged it in to one of the plugs i built on the floor rather than right up next to the variac. I can see it at a glance when i want to and it's not shining in my face all the time.

    Thanks for the advice / confirmation on this - it's exactly what i was looking for.
     
  20. robrob

    robrob Poster Extraordinaire Ad Free Member

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    I only use the variac on my bench. I have a bucking transformer for everywhere else.
     
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