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Please tell me what current amp this TEISCO CHECKMATE 20 is closest to....

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  • #31
    A transformer can make any voltage you design it for.

    A transformer is two coils of wire wrapped around a common iron core. The primary coil is what connects to the wall outlet. The secondary is what we connect to for our circuits. Transformers work by "turns ratios." If my primary side has 100 turns - 100 loops in the winding coil - and my secondary coil has 200 turns, then the voltage will be stepped up to twice the primary voltage. So 120v in and 240v out. If my primary was 100 turns and the secondary 50 turns, then it steps down to half, or 120v in and 60v out. By changing the turns ratio, my 120v in primary can make any voltage I want in the secondary.

    If I have a ten to one ratio, my 120v in makes 12v out. If I connect that same transformer to 240v instead of 120v, then I'd get 24v instead of 12v. It is all about the turns ratio. And yes, if I hook it up backwards and I put my 120v into the secondary coil, I'd wind up with 1200v on the primary coil.

    SO I can make a transformer to any voltages I want. By wrapping additional coils around the iron core, I can have additional voltages. So for example with my 120v primary (or 240v, whichever we are designing for) I can have one winding producing 350vAC, and a second making 6v for heaters. So one steps up and one steps down on the same transformer.
    Education is what you're left with after you have forgotten what you have learned.

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    • #32

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      • #33
        Juan makes an excellent point in outlining safety concerns over step down transformers (and the same applies to step up). Many of the small low-wattage transformers available to convert 230v>120v are not isolated and are what are termed an 'autotransformer'. Their purpose is to be able to run an imported (US or other) piece of equipment from a higher voltage wall supply, or vice-versa. These offer no mains isolation and are dangerous to use in constructing a tube amp of any kind. They can only be used as a plug-in unit to run an item of equipment as if it was being used in the country it was manufactured for.

        There are however isolation transformers that are used to provide a supply for the purpose described above. Confusingly these are often not marked as such and I've been fortunate in discovering some of these in a batch of redundant power supplies that I originally dismissed as containing autotransformers. Additionally, there are isolated industrial transformers that are used to satisfy safety requirements - I have some that are intended to power industrial control panels and these make excellent tube amp supplies.

        The best advice I can offer is that unless you know without doubt that a step-up/step-down power supply is isolated, then assume it to be an autotransformer and don't even think about using it in a tube amp build.

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        • #34
          Originally posted by aaron View Post


          Also, Mick, Olddawg, Justin, & RJB, I owned a Epi VJr. v3 for a while, and it just didn't make it for me, sonically, so I sold it. I also have SS amp (Fender M-80) and an effects pedal, and I am also not satisfied with that either. I'm not going to enter the tube vs. SS argument, b/c I don't really have an opinion.

          I've kind of been bitten by the tube bug... and I've already suffered for many years with the "buy a fixer upper" bug for MANY years, and it usually worked out for me.
          There are only a couple of ways of getting power tube amp saturation distortion at low volumes. The two easiest ways are a low wattage amp (5 watts or less)and a speaker power attenuators. That Tiesco is going to be clean and loud before it breaks up. If you are using a modeling pedal it won’t matter a whole lot what you are plugging it into (tube or SS) as long as you have a compatible speaker. It could be the power amp in your home stereo.

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          • #35
            Don't worry, this whole thread was about an amp that already has the transformer in it.

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            • #36
              I understand. The clarification is for anyone else looking at this who may get the wrong idea about mistakenly using an autotransformer in an amp build. There are quite a lot of people worldwide of varying levels of understanding and ability that arrive here so it's essential that there's no doubt or ambiguity. It's good to have peer review and critical comment - it makes sure standards are maintained.

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              • #37

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                • #38
                  Sorry if my comment came out sounding harsh.
                  I know OF COURSE commenters know the difference, and Aaron would catch up, my worry was about any third party who might read this in the future and understood it as: "2 say you can use it as a PT, 1 says no, yes wins 2:1" , or "it can be done both ways, it´s just a difference of opinion" so I had to be somewhat emphatic.
                  Juan Manuel Fahey

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