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    Hi!

    I have a power transformer that I'm planing to use in a build. When I'm measuring the taps I get the result presented in the attached picture.

    Click image for larger version

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    I wonder about the orange and purple wires. I get approximately 40 Vac across the orange wires. Between these two orange and a purple I get roughly 20 Vac.

    What are these orange wires for? Is the purple some kind of center tap?

    Thanks!
    In this forum everyone is entitled to my opinion.

  • #2
    Originally posted by überfuzz View Post
    Hi!

    I have a power transformer that I'm planing to use in a build. When I'm measuring the taps I get the result presented in the attached picture.

    [ATTACH=CONFIG]57729[/ATTACH]

    I wonder about the orange and purple wires. I get approximately 40 Vac across the orange wires. Between these two orange and a purple I get roughly 20 Vac.

    What are these orange wires for? Is the purple some kind of center tap?

    Thanks!
    Are you measuring this with a load? if not when loaded your voltages will be lower.
    Orange wires who knows the purple is a center tap.

    What did the transformer come out of? If it was new what did you buy it for?

    nosaj
    Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

    Comment


    • #3
      Originally posted by nosaj View Post
      Are you measuring this with a load? if not when loaded your voltages will be lower.
      Orange wires who knows the purple is a center tap.

      What did the transformer come out of? If it was new what did you buy it for?

      nosaj
      It's from a scrapped amp, I think it is, or was a bugera. I figured that the orange taps were from some solid state circuitry. But that's just a guess...
      In this forum everyone is entitled to my opinion.

      Comment


      • #4
        Are you sure about 10 ohms on the 6.3V winding? That is unusually high for a tube application. If the load regulation were 10% then the transformer would only be supplying 63mA, not enough for even a 12AX7 ( 300mA). I would expect at most tenth of that and more like 1/100th. It's very hard to measure resistances under 10 ohms with any accuracy with an ordinary DVM.

        A better way is to measure the output voltage unloaded and then again into known load of say 8 ohms. The voltage drop divided by the current is the source impedance which. If you then subtract the primary resistance divided by the turns ratio the result will be close to the winding resistance.

        The orange/purple/orange wires would be suitable for providing a regulated +/- 15V supply for opamps.

        How big is the transformer? What was it pulled from?
        Last edited by nickb; 04-05-2020, 06:26 PM.
        Experience is something you get, just after you really needed it.

        Comment


        • #5
          Your DCR measurements don't seem to make sense. A heater winding with a DCR of 10R would be rather useless. Even a single 12AX7 with a heater current of 0.3A would load down the voltage by 3V. I would expect a heater winding DCR way below 1R.

          Also the DCRs between the orange wires and the purple wire don't add up to 18R.

          Please check your meter: battery, calibration and verify accuracy with known resistors.

          To exclude meter errors caused by inductance, short the primary while measuring secondary DCRs. But I don't think that's your problem.

          Edit: Just noticed Nickb beat me.
          - Own Opinions Only -

          Comment


          • #6
            The PT might have come from the Bugera Vintage 55?

            Comment


            • #7
              Originally posted by TomCarlos View Post
              The PT might have come from the Bugera Vintage 55?
              That seems to be the one.

              Thanks!
              In this forum everyone is entitled to my opinion.

              Comment


              • #8
                Great. If the PT has a part number on it, can you post it here? That info could be helpful to others.

                Comment


                • #9
                  I feel so stupid... Why didn't I just look at the S/N number from the start.

                  Manufacturer P/N: E10166 (R1L) It might say EL0166(R1L) hard to say as it is a bit nicked.
                  Bugera P/N: 333-EU
                  Date code: 0813
                  In this forum everyone is entitled to my opinion.

                  Comment


                  • #10
                    OK, so a PT for a Bugera 333. PArt was made in 13th week of 2008.

                    The light grey wires are the high voltage.
                    The yellow wires are the 6vAC for heaters.
                    The orange wires are the low voltage AC for the 24vDC supplies, Violet wire is center tap. Roughly 35v center tapped, or 18-0-18 if you prefer. (Oh, I see you got 40 and 20, so close enough.

                    That low voltage supply also powers three 12AX7 heaters in the preamp. The 6vAC heats the four power tubes and a 12AX7 phase inverter.
                    Education is what you're left with after you have forgotten what you have learned.

                    Comment

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