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  • Cheapest power supply transformers?

    Power supply transformer prices are bumming me out.

    Anybody know of any super cheap power transformers for powering tube amps?

    Most of the ones I can find are 60 bucks and up.. I would like to build some amps to give away to my friends but I don't want to spend much. If I could build little amps for less than 50 bucks in parts I could sell them for 100 bucks and still make money! I have lots of speakers and tubes and sockets to get started, I just need resistors filter caps and power supplies.


    I found these http://www.mouser.com/ds/0/Triad-Mag...-68X-29904.pdf for 11 dollars! I could run it backwards to get 220 volts or dual 110. If I needed more volts I could just run two or more rectified in series. Still have to figure out heater power though.

    Anybody know of any other possible cheap power supplies for low power little amps?

    N-68X Triad Magnetics | Mouser

  • #2
    In most tube amps, the power transformer is the single most expensive part in the amp. The output transformer is often a close second. The resistors, caps, tube sockets, etc. are almost negligible. Chassis, enclosure, speakers, controls and switches are also bigger ticket items.

    Then there's the cost of safety. It's important to remember that even one consultation with a lawyer about why this widow or parent is suing you will cost a lot more than you'd make on an amp. So it's really crucial to know how to be sure that anything you ever give/sell to anyone else is made with safety rated parts and wired correctly to not let the high voltage AC and DC in the amp get loose and either kill someone or start a fire.

    Little amps seem safe enough - but that AC power line coming into it hooks to a power station capable of starting fires all day long and not even breaking a sweat; and it only takes about 20ma of 60 cycle AC current to sent some hearts into fibrillation.
    Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

    Oh, wait! That sounds familiar, somehow.

    Comment


    • #3
      One problem with running small PT's backward to get higher voltages is the primary coil insulation probably isn't up to the task. Attempting to run them in series would only exacerbate the problem. Also, a step down transformer run backwards loses current rating in proportion to the voltage increase. So the proposed transformer, which is already marginal, would then be far more marginalized (two dollor word...FREE). Probably the cheapest way to get "affordable" PT's (and OT's) is through ham shows and swap meets. Perhaps Ebay. China makes some cheap transformers. Not too easy to find, but they're out there. I've run across them a couple of times accidentally. How else could LOUD technologies build a complete tube combo amp with reverb for under $300 US retail!?!
      "Take two placebos, works twice as well." Enzo

      "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

      "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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      • #4
        Anteks are pretty cheap, 240VDC with heater taps are ~$25

        Comment


        • #5
          I understand the importance of safety, the specs on that cheapo isolation tranny I was thinking about running backwards say: "Safety:
          These units are designed with 1500V isolation between winding to winding and
          between winding and core. Materials and construction are rated for Class B
          insulation system." So I was just hopoing that this translates to "safe enough"...

          Shoudn't it be able to put out about 200ma ran backwards if it can put out 435 ma normally?
          Tedmich: Which antek tranny are you thinking about for 25$ with heater winding? Thanks

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          • #6
            quite a few, but lower current than you seem to want, what are your design requirements?

            The old Real McTube (a Fred Nachbaur design, RIP nice guy!) used two back to back 120/12v supplies to feed a 12ax7, quite safely and its possible to double, rectify and smooth wall AC to ~300vdc with many DCDC converters doing this safely. There are machine transformers used to make 120VAC into various higher valtages which can sometimes be had cheap but they aren't CT


            BUT you cannot go cheaper than big companies, can't be done.
            SMPS can work but its for weight not $ typically.

            you could explore Alibaba and try looking for the Chinese low ball, like everyone else!

            Comment


            • #7
              That 1500V isolation is literally from winding to winding and from winding to core and absolutely NOT from turn to turn. Also, I don't care how they rate that secondary, your not going to power a Super Twin with a transformer that's roughly 2.25" X 2.25" X 3.25". Just not going to happen. The derate happens when you run the primary in series as a step up secondary. The volts and current equate to power and this causes heat. There is only so much heat a transformer can dissapate based on it's size and construction. Asking that transformer to deliver it's rated current at twice the voltage is like doubling the gear ratio on a bicycle and expecting to go twice as fast for the same amount of pedal pressure. Also just not going to happen.

              Then there's the added expense of the filament transformer. You do need to heat the tubes.
              "Take two placebos, works twice as well." Enzo

              "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

              "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

              Comment


              • #8
                Go to http://www.diystompboxes.com/smfforum/ (link is on this forum under "guitar effects") and search either "tube amp" or any designs by frequencycentral. (There are other designs too but I know for sure that he has designed a couple.) They have been doing some pedal-sized, low-wattage guitar amps using switch mode power supplies and charge pumps. Still need an output transformer but the power supply can be run off a wallwart and a handful of fairly cheap components.

                Comment


                • #9
                  Maybe you could make them pedals?

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                  • #10
                    And just in case you haven't found them Weber and Magnetic Components ( can be purchased through Triode Electronics) are the most in expensive I've seen intended for tube amps.

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                    • #11
                      Look into Edcor. They seem to have a number of designs available, many suitable for small tube amps at reasonable pricing.

                      I've only purchased one piece from them so far, but quality is good. They build when you order, so it may take 6-8 weeks to get your order. And I guess that for a price they will create exactly what you need and build one or a hundred.

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                      • #12
                        The Antek transformers seem by far better than anything I have seen so far, pricewise and feature. I have never used a toroidal type tranny, are there any drawbacks? It seems too good to be true.. Thanks very much for the replies!

                        Comment


                        • #13
                          A cheap DC-DC SMPS with a laptop PS could work, e.g., 12V 4-5A PS could easily power bunch of tubes, and the SMPS takes care of the HV (also powered from the laptop PS). I recently rig one up just to see if the SMPS would be noisy as many have claimed... Alas, it worked just fine, and it was not noisy. For both the SMPS and laptop PS (bought them brand new), I paid <$10 (in China, don't know if the same could be had elsewhere). Anyway, if you have some old laptop power bricks laying around, give them a try.

                          Jaz

                          Comment


                          • #14
                            That 1500V isolation is literally from winding to winding and from winding to core and absolutely NOT from turn to turn.
                            There's double lacquer insulation wire that has a 2-3kV specs on the insulation. So you get 4 layers of lacquer between two turns of wire in a winding.
                            However when wire is wound (bended) this rating decreases to some degree. I've seen many power transformers and couple of output transformers without any winding/layer insulation.

                            Comment


                            • #15
                              Originally posted by Austin View Post
                              The Antek transformers seem by far better than anything I have seen so far, pricewise and feature. I have never used a toroidal type tranny, are there any drawbacks? It seems too good to be true.. Thanks very much for the replies!
                              You have to be careful to use full wave rectification on each winding. No half wave rectifiers like in bias supplys.
                              WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
                              REMEMBER: Everybody knows that smokin' ain't allowed in school !

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