Constant voltage

Discussion in 'Shock Brother's DIY Amps' started by RollingBender, Jul 25, 2019.

  1. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    I’m getting a bit frustrated working on amps, doing things that are voltage dependent, and then discovering that the wall voltage when I started a project is not the same as when I complete it.

    Last night I was messing around putting together a bucking transformer for my latest build. Started testing with 121.4 at the wall, checked some time later and it was 114.7.

    Anyone use a fancy device to keep a steady voltage? Is this something that can be built affordably?
     
  2. bblumentritt

    bblumentritt Tele-Afflicted Platinum Supporter

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    Use a VariAC. A variable AC transformer.

    I use one on all my builds, and always test at 119.5 - 120.5 VAC. My wall voltage is usually around 122V.

    The Variac is also good for low voltage testing a new build.
     
  3. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    Isn’t a variac still relative voltage once set? Meaning... wall at 120, set variac to 115 and then the wall voltage dips down lower than 120, the output voltage would also dip down?
     
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  4. King Fan

    King Fan Friend of Leo's Ad Free Member

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    You can get consumer-grade voltage regulators for $50-100 (Tripp, APC, etc.). But read the fine print and you’ll see they tend to have only one 'boost' and one 'buck' level, and worse, they only regulate if the power goes outside a 20 or 30V range.


    Sent from my iPad using Tapatalk
     
  5. brokenbones

    brokenbones Tele-Meister

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    I've been using a simple (old) variac with a kiil-a-watt meter plugged into the output. I did find a housed variac recently at a ham fest for $10. I ordered one of those digital AC line meters off eBay that i'm going to install on the face. Anything with an output meter will solve your dilemma.
     
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  6. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    From 9:30 to 10:30 in this video....that’s the holy grail of power regulators.



    There has to be a 120vac buildable version of this out there.
     
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  7. aerhed

    aerhed Friend of Leo's

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    Any UPS with an inverter will work. Might be a little buzzy.
     
  8. Wally

    Wally Telefied Ad Free Member

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    Yes. However, at the bench one can assure that the voltage that you desires is being applied at the time of the testing...you check the voltage, set it, and then your tests...whether Sonic or electronic...are done. At, least that is the way I use it. I also use it to note differences at different voltages and to assure that someone doesn’t get caught with biasing that is too hot when the user is having to use a higher voltage than they might prefer. Ex: I did some work on an amp for a fellow who shipped the chassis from Wisconsin. He informed me that he used a voltage controlled situation when o,ay8ng..,he used 117VAC for this vintage ‘65 Deluxe Reverb. So, I set the bias for that voltage and made sure that IF h got caught without the voltage control device that his amp would be good to go at say 123VAC from the wall.
    As for Sonic differences, it is interspersing to listen to the difference in the amp at different voltages even after setting the bias to the same plate dissipation. After all, all of the other tubes in the court are cathode biased, so a voltage change rebiases them as well.
     
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  9. BobSmith

    BobSmith Tele-Meister

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    Exactly how I do it.

    See my video testing a 5e3 recently. From 0:10 I explain the setup.
     
  10. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    I monitored the wall voltage all afternoon today. Lowest was 112.5, highest was 119.2. In a 20 minute span, I saw the 112.5 to 116.9 swing. Not only frustrating with something on the bench, while playing, that’s a big enough swing to take heater voltages out of spec limits. I’ve A/B compared voltage differences of that degree and it absolutely effects how an amp sounds and behaves.

    A variac wouldn’t fix that unless you were constantly monitoring and making appropriate adjustments.
     
    Last edited: Jul 26, 2019
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  11. Wally

    Wally Telefied Ad Free Member

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    I have seen my wall voltage in the shop go from 122+VAC in the AM too just over 111VAC in the hot afternoon. Firms Industries builds a unit to provide a stable voltage level to combat this problem. It costs a piece of change, though.
     
  12. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    Looked up the specs on the UPS w/inverter. It does take care of spikes and brown conditions but, like aerhed points out, it’s a pretty big sweep...10% either way of 120.

    The Kikusui like Angus uses has a 1% range and you can set the middle where you want. The cheapest one I’ve found is $2,500!!!

    Wish I could hack the UPS idea to tighten up the range of monitoring. They are noisy though.
     
  13. BobSmith

    BobSmith Tele-Meister

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    That’s true. But that voltage swing is outrageous. It doesn’t seems right to me. You should contact your power company. The voltage can/should be fairly well regulated by the utilities. Maybe there’s a problem.
     
  14. BobSmith

    BobSmith Tele-Meister

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  15. peteb

    peteb Friend of Leo's

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    This sounds like a logical first step.


    The power company will probably not be too concerned, but it would be beneficial to hear from them what is to be expected.
     
  16. RottenTheCat

    RottenTheCat Tele-Meister

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    You dont wantca variac, but a constant voltage transformer like those from Sola. I deal With this all the time at work

    (edited in...)

    Here's a link:
    http://www.solahevidutysales.com/cvs_hardwired_series_power_conditioner.htm

    The wiring diagrams:
    http://www.solahevidutysales.com/pdf/powerconditioners/elecconns.pdf

    From Sola's literature:
    "Superior voltage regulation of ±1% sets the CVS Series power conditioner apart from other power conditioning technologies on the market. Extremely tight regulation is accomplished by Sola/Hevi-Duty’s patented ferroresonant transformer technology. The CVS Series power conditioner recreates a well regulated sinusoidal waveform that is well isolated from input disturbances including impulses, swells, sags, brownouts and severe waveform distortion."

    We sell a dozen or more of these every year for sensitive electronics placed on lightning and brownout prone golf course power. They work.

    You can DEAD SHORT the output, and there's no damage. The magnetic field simply collapses and that's that, nothing happens. When you open the circuit, it instantly restores itself.

    CAUTION: You do not want to "oversize" the unit for its application. That is, 500va unit will supply you the power you need, just over 4 amps worth at 120v out. These are made to run best at their maximum capacity. If you say... oh heck, let me get the 1kva unit, and be covered for "anything", the unit will run hot when you're only putting a 1amp or 3 amp load on it. Use the smaller unit. And, these run a bit warm normally, in perfect operation.

    Feed it just about anything in, and you get 120 out. Its that simple. And, no stepped square wave waveforms like a "battery backup" or UPS. That's why I use 'em!
     
    Last edited: Jul 28, 2019
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