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AC Power for Testing @ 220V+

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  • AC Power for Testing @ 220V+

    I'm in the US and I'd like to build a blackface type amp for someone in Switzerland. I can get the power transformer I need easily enough, but I'm wondering what you all use for bench testing an amp at 230V / 50Hz, or other international standards. Are there any reasonably priced commercial units? I suppose I could build my own power source using a variac and step up transformer. What about the difference in frequency? Is it significant for audio purposes, or can it be ignored? If anyone has built their own test rig, I'd love to hear about it.

  • #2
    Originally posted by Fletcher Munson View Post
    I'm in the US and I'd like to build a blackface type amp for someone in Switzerland. I can get the power transformer I need easily enough, but I'm wondering what you all use for bench testing an amp at 230V / 50Hz, or other international standards. Are there any reasonably priced commercial units? I suppose I could build my own power source using a variac and step up transformer. What about the difference in frequency? Is it significant for audio purposes, or can it be ignored? If anyone has built their own test rig, I'd love to hear about it.
    For 60Hz power, 220-240V, we have a large collection of 2kVA Step-Up transformer boxes (I forget who the mgr is), which has a 12AWG 120V Nema 5-15 Plug for our domestic power, and the Shuko-style 220VAC Outlet. If I need to dial in either 220V or 240V, I'll plug it into my 0-140V/30A Variac, and can monitor the output on a separate Valhala 2101 Power Analyzer. If I need 50Hz Power, I have an Elgar 1127 AC Power Source, which has variable frequency and variable AC Voltage Range. This was made for Interpower (the big blue box) having every common European Connector Format on the front panel, instead of the single Shuko style round 2-pin connector with GND).

    https://www.interpower.com/cgi-bin/i..._part=85522201

    This link shows the current model of that Elgar-mfgr'd product for Interpower. I have an earlier version of it.

    I used to have a large 0-280V/15A Powerstat (variac), which if wired for 0-140V input, you can dial up 0-280V on the output, but I ended up selling it. You can still find variacs that have that range, though not so common, and no doubt would be expensive. I'll check at our rental depot for the mfgr's name on the heavy step-up xfmr boxes we use.
    Logic is an organized way of going wrong with confidence

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    • #3
      Use a "universal" transformer. In other words, some amps are ready to work on either 120 or 240. Some have a switch for that, others have to be wired for it. But in this case, there are two 120v primary windings. For 120v you wire them in parallel. For 240v you wire them in series. SImple as that. Build the thing with primary wired for your 120v. Then once it is done, rewire the primary for 240v.

      Will this have a hard wired power cord or will you use the common detachable IEC cord?

      The 50/60 thing shouldn't matter, especially on the 240 ready transformers.
      Education is what you're left with after you have forgotten what you have learned.

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      • #4
        You don't have 220v for washer/dryer or stove?

        I have a few 220v outlets at home, not to mention work.

        I have the opposite problem, a customer from Australia wants his turntable and amp converted to 120, but they aren't switchable.
        Not really worth a step up trans for them.

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        • #5
          @nevetslab That is one nice piece of kit but, as I feared, well outside my price range.
          @Enzo Thanks for that. Great advice, and that'll get the job done the quickest and easiest, but I think I want to build a rig for this and future jobs.

          My thought is to use my 0-140V variac as an external variable control, then build a box with a step up transformer, voltage meter, and a variety of international sockets on the front panel for the output. Should be pretty cheap and simple.

          Anyone have a recommendation for a step up transformer?

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          • #6
            Originally posted by Fletcher Munson View Post
            @nevetslab That is one nice piece of kit but, as I feared, well outside my price range.
            @Enzo Thanks for that. Great advice, and that'll get the job done the quickest and easiest, but I think I want to build a rig for this and future jobs.

            My thought is to use my 0-140V variac as an external variable control, then build a box with a step up transformer, voltage meter, and a variety of international sockets on the front panel for the output. Should be pretty cheap and simple.

            Anyone have a recommendation for a step up transformer?
            I called over to our Guitar Dept, and we have a collection of PowerBright VC-500W & VC-1000W Step-Up/Step-Down transformer boxes. These range from 100W, 200W, 300W, 500W, 1000W, 2000W & 3000W.

            https://www.amazon.com/dp/B000MX564U...ding=UTF8&th=1
            Logic is an organized way of going wrong with confidence

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            • #7
              Like drewl, I would just use the 220 you have in your house. Sure, you don't need 30A service, but the amp fuse should suffice for protection. Build an adapter M-F, and use whatever fixture the amp needs, 12 ga extension should be adequate.
              You'll spend a lot less than investing in transformers!

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              • #8
                And just as a tech, after 50 years of this, I might have needed to power up a 240v unit maybe twice at most. If I were looking at investing in a 120/240 step up just for the bench, I think I would invest in an additional variac or additional 120/120 iso first, any one of a number of things. Better solder gear to further my SM soldering say. Gonna need that a lot more.
                Education is what you're left with after you have forgotten what you have learned.

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