Is a Variac a must have item??

Discussion in 'Amp Tech Center' started by Favata2020, Jun 20, 2020.

  1. Favata2020

    Favata2020 TDPRI Member

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    Just wondering if a Variac is always needed when changing filter, bias or any E caps in an amp?
     
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  2. elpico

    elpico Tele-Holic

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    nope
     
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  3. LightningPhil

    LightningPhil Tele-Meister

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    Second the nope.

    Mainly use my one for dealing back the power in the mash kettle when making beer. Or increasing the voltage feeding the extension lead to the lawnmower (which is obviously the sensible thing to do). Never used with amps unless purposely running them at lower voltage for less headroom, which is rare and easy to achieve for less cost with a resistor.
     
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  4. DavidP

    DavidP Friend of Leo's

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    Its a great tool for me when breaking in new speakers (via the ol' Uncle Spot/Ted Weber method).
     
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  5. Dacious

    Dacious Poster Extraordinaire

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    Not really. You can build a lightbulb limiter for safe startups if needed.
     
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  6. Paul G.

    Paul G. Friend of Leo's

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    Make a lightbulb limiter for a few bucks and have safe startups.

    A variac is nice to have (the cheapo Chinese ones are fine for the hobbyist) but not a necessity.
     
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  7. dan40

    dan40 Tele-Afflicted

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    I bought one years ago and the only thing I have used it for was breaking in speakers like DavidP mentioned. A light bulb limiter is much more useful for building and troubleshootinhg.
     
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  8. Jesco

    Jesco TDPRI Member

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    I have found mine useful for testing unknown power and output transformers.

    Whether they are necessary for "forming" new capacitors is a matter of debate that I have found no consensus on.
     
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  9. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    ^^^^
    Agree with above. Great for putting voltage on unknown transformers to find winding ratios etc.

    I also use it for first power up without *tubes in* to make sure caps do not see too much voltage. You don't want 500V on your 475V caps.

    Not a must have but I will keep it. Watch used prices if you decide you want one.
     
    Last edited: Jun 21, 2020
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  10. Favata2020

    Favata2020 TDPRI Member

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    So, if Ive just replaced all the caps in my amp I can just fire up the amp and not worry avout blowing the caps?
     
  11. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    Most people do. I would put a light bulb limiter, or something to drag down the voltage a little. Coil up a 100 ft extension cord with a heater connected.

    The tdpri member in Phoenix says the wall voltage is 110VAC in the daytime when everyone is running the air conditioners.

    The next guy will tell you to make it take it.:lol:
     
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  12. Favata2020

    Favata2020 TDPRI Member

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    Thank you!! sounds like a plan!
     
  13. Milspec

    Milspec Poster Extraordinaire Silver Supporter

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    Nope, not necessary, but nice to have.

    It is a lot like installing a new engine in your car. Some will tell you to drive it easily for a month to break-in the engine while others subscribe to driving it like normal or even pushed a little harder than normal. Just depends on which camp you find yourself in really.

    I will say that you can find a vintage Variac for cheap, so no need to buy a new China built model or even build a lightbulb limiter in my view. For $40 your should be able to find a good used US-built variac. I purchased one about a year ago that looks fresh out of the box from a science lab at the local college. I think it ran me $42. I use it mostly when working on my old Trans-oceanic SW radio sets from the 1940's. it doesn't see much use with my amps, but voltages in my area are very steady at 117 volts.
     
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  14. Engine Swap

    Engine Swap Tele-Holic

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    I have a couple vintage ones that I got for cheap. Nice to have, especially for new builds and troubleshooting.
     
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  15. Switchy

    Switchy Tele-Afflicted

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    Look who we got here, somebody that thinks he's Eddie Van Halen.
     
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  16. Dacious

    Dacious Poster Extraordinaire

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    That's what Leo and Jim did. Soldered "em, fired 'em up, no sparks, sounds OK - box 'em up, ship 'em out.

    A good test is tubes out, fireup and make sure there's B+ at the plate pins. It'll be a bit higher due to no load.
     
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  17. Paul G.

    Paul G. Friend of Leo's

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    New caps should be formed already unless they've been sitting in a warehouse for a long time. Starting up new caps easy just prevents damage to caps that might have a weak or depleted oxide. Current limiter is fine, variac better but not absolutely necessary.
     
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  18. BobbyZ

    BobbyZ Doctor of Teleocity

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    If you believe everything Gerald Weber says, then you need one.
    However some things that get missed with starting at real low voltage and coming up slowly.
    If the amp has a tube rectifier you'll want to bypass that with diodes. Because the tube isn't going to pass DC on to the the filter caps, until it gets up to a voltage where it can.
    Other thing is shorts. If you have a short somewhere it's still a short at 10 volts.
    Never thought about that till I got a veriac and wanted to finally charge the caps "the right way". Dug up some diodes and put a light bulb limiter between the veriac and the outlet.
    Then I went back to just using the light bulb limiter, mostly in case I screw up.
    Been a few years since I used the veriac for anything.
     
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  19. Favata2020

    Favata2020 TDPRI Member

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    Very good info and tips from all of you! I just want to do things the right way without fear of destroying an amp! I could see that newer caps should be able to be used right off the bat where the NOS ones would need to be babied more!
     
  20. schmee

    schmee Doctor of Teleocity Silver Supporter

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    I have one. Never use it. Caps? I'm in the minority probably but I doubt major amp builders take the time to "form" caps. I just turn 'em on.
     
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