Is a Variac a must have item??

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

  1. bblumentritt

    bblumentritt Tele-Afflicted Platinum Supporter

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    I use a VariAC, as well as a light bulb current limiter.

    The voltage at my house is usually 122-123. I set my variac at 120 so that I get consistent results across the board when testing.... comparing apples to apples so to speak.

    Also, at trade shows, I've seen line voltages of 130+, so I definitely use my variac there!

    I don't use it to break in speakers. 60Hz is below the resonance of the speaker, and usually about 7-8dB below the 120Hz response, and the hum is most annoying.
     
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  2. jhundt

    jhundt Doctor of Teleocity

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    I found some old variacs, and built a nice enclosure with a big old analog volt-meter. It was the coolest-looking piece of equipment in my shop.

    So - there's that. On the 'cool-looking things in the shop' scale, variacs with large old-fashioned needle readouts are spectacular. And that's important in a way. Because when you step into your shop, you want to feel that you are entering a very special place. And a variac can do a lot to create that image.

    I found the variac not-especially useful. All that stuff about 'bringing up caps' is (in my opinion) not necessary.

    It was useful sometimes to drop voltages for testing, and sorting out transformers, as mentioned above. etc. The light-bulb limiter does not replace a variac for those purposes.
     
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  3. Kevin Wolfe

    Kevin Wolfe Tele-Meister

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    I use both as well. They are totally different tools and are no interchangeable in use.
     
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  4. Ten Over

    Ten Over Tele-Holic

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    You don't need a variac. You don't need lots of things. But like the variac, they're fun.
     
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  5. 24 track

    24 track Doctor of Teleocity Silver Supporter

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    it is just another screwdriver in your box if you have one , another tool to use if you need one
     
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  6. Favata2020

    Favata2020 TDPRI Member

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    it never fails. when I have money to buy a vintage one, they are either way overpriced or nonexistant! smh
     
  7. Javier668

    Javier668 TDPRI Member

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    No
     
  8. Jowes_84

    Jowes_84 TDPRI Member

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    If you think you need something close to a variac, you can build a lightbulb limiter and voltage regulator all in one. Here is mine. Does not look safe;) but it works great. On the shorts... as soon as the bulb flashes up brightly when it shouldn’t, you know something is wrong.
    AEA6E04D-FFB1-4325-910A-A487BA7D7348.jpeg
     
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  9. Kevin Wolfe

    Kevin Wolfe Tele-Meister

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    How does it regulate voltage?
     
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  10. Jowes_84

    Jowes_84 TDPRI Member

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    Hi
    Well. With works great I did not mean that it replaces a variac well. It simply works like a dimmer - cuts off the Lobes.
    I try to avoid using that feature alone but in combination with a lightbulb it’s useful for starting up a new build, as I don’t have anyone reviewing my work.
     
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  11. galtjunk

    galtjunk TDPRI Member

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    I only use one when I pull an old amp our of storage.
    It may not be necessary but I already have the variac.
    I use a light bulb limiter on new builds.
     
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  12. Kevin Wolfe

    Kevin Wolfe Tele-Meister

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    I like a Variac to test transformers. It’s an easy way to figure winding ratios and thus reflected impedance.
     
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  13. Favata2020

    Favata2020 TDPRI Member

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    I thought about going to Lowes and buy a light dimmer switich and then wiring it in an extension cord...simple and it should work
    no lights needed
     
  14. Kevin Wolfe

    Kevin Wolfe Tele-Meister

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    The idea behind the light bulb is that it’s a visual indicator that somethings wrong.
     
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  15. Favata2020

    Favata2020 TDPRI Member

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    good point!!!
     
  16. trobbins

    trobbins TDPRI Member

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    I nearly always use a variac along with a plug-in type cheap mains AC power meter. The meter is to indicate mains voltage if I want to check what it is for a benchmark test, but is normally set for current to indicate if anything is NQR.

    Some common uses I find for the variac are:
    - when first powering on a repair or prototype or restoration. A tube rectifier can be replaced with a ss plugin clone, so I can check that B+ and bias levels are rising as expected from zero. If valves are out then I can step up B+ to a level without exceeding any preamp supply electrolytic or coupling cap voltage rating, and can check coupling cap leakage levels in-situ at their rated voltage levels, and all circuitry and valve pin expected voltage levels in case some part got left out or is open-circuit.

    - similarly if I am faultfinding or tweaking a specific valve stage (eg. for gain or frequency response or screen voltage or faultfinding) then I don't need all the other valves in, and can just set B+ up for ok testing level.

    - similarly if faultfinding a blown vintage ss transistor amp, a variac is great to bring up enough supply rail voltage to indicate voltage levels around transistor circuitry and identify suspect parts. Output stage bias can be tweaked up with a lowered mains voltage and then raised to confirm ok level, as some old bias pots are intermittent or have setting paint slathered all over them. Replacing secondary side fuses with current sense resistors also helps confirm balanced ok operation - and sort of act similar to a light-bulb limiter until operation at nominal voltage is confirmed.

    I typically only use a lightbulb limiter if I need to quickly confirm that some vintage equipment is still ok if I haven't used it for years, but I know it was working ok.
     
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