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determining the secondary taps on an OT

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  • determining the secondary taps on an OT

    I just wanted to double check that the following methods is safe and accurate. (I think it's fine, but just in case...)

    So I have a Heyboer OT I had wound a few years back, and I can't find the lead chart or any documentation for it. I know what the Zpri and Zsec taps are, I just can't remember what color is what. There are taps for 4,8, and 16Ω.

    I was going to connect the what I think the 16Ω tap is to a load and measure, lets say 15V at the output (or whatever). I was then going to take readings at the other two taps to determine the 8Ω and 4Ω leads.
    with 15V at the 16Ω tap, I should read the following at the other two:
    8Ω ≈ 10.6V
    4Ω ≈ 7.5V

    correct?
    If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

  • #2
    yes
    Juan Manuel Fahey

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    • #3
      As long as you've correctly guessed the common tap, you're good to go. Otherwise you may be hunting for a little while.
      If it still won't get loud enough, it's probably broken. - Steve Conner
      If the thing works, stop fixing it. - Enzo
      We need more chaos in music, in art... I'm here to make it. - Justin Thomas
      MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey

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      • #4
        And you are only interested in getting them in order. Ignore the urge to calculate "OMG this appears to be a 6.9 ohm tap..." Low, medium, and high is close enough. Once there, you know which is which.
        Education is what you're left with after you have forgotten what you have learned.

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        • #5
          if you didn't request some certain color scheme you probably got this

          heyboer ot
          4 - yellow
          8 - green
          16 - orange

          Black is common.

          also if the OT still has the sticker on it they might be able to look up the spec sheet by part number

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          • #6
            I was going to connect the what I think the 16Ω tap is to a load
            No load required.
            - Own Opinions Only -

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            • #7
              Originally posted by nsubulysses View Post
              if you didn't request some certain color scheme you probably got this

              heyboer ot
              4 - yellow
              8 - green
              16 - orange

              Black is common.

              also if the OT still has the sticker on it they might be able to look up the spec sheet by part number
              This was my best guess and is how I have it wired. Thanks.
              If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

              Comment


              • #8
                But did you actually check it?

                As in measuring a couple voltages?
                Juan Manuel Fahey

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                • #9
                  Originally posted by J M Fahey View Post
                  But did you actually check it?

                  As in measuring a couple voltages?
                  Not yet. I don’t have it at work, Im going to measure it after I get home. Promise
                  If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

                  Comment


                  • #10
                    Originally posted by SoulFetish View Post
                    This was my best guess and is how I have it wired. Thanks.
                    If the amp works and can be plugged in, use a sine wave to play it into a dummy load. if you can measeure current draw either via cathode resistor or a bias probe all you have to do is make sure the amp works the same on all settings. Meaning, if it's a 50W amp or whatever, does it put out 50W on all settings, 16 ohm tap into 16 ohm load, 8 tap load into 8 ohm load, etc? Power tubes should reach clipping at the same current draw on each setting. I feel like I usually see most power tubes clip at around 130 mA

                    if you have it hoooked up wrong it will be pretty apparent. for instance ifyou have a 8 ohm tap from OT hooked up but are using an 16 ohm load, and the amp is 50W it will proably put out around 35W at clipping and the power tubes will clip at 80-90mA or so rather than ~130mA.
                    Last edited by nsubulysses; 01-16-2019, 08:04 PM.

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                    • #11
                      I measured voltages at all taps and I can confirm that the secondary leads match what you posted and I suspected.
                      I tested the output into each respective load, using a constant sine wave input voltage. Measuring VRMS2/R, output power all measured within .04% of each other.
                      Interestingly, when I was monitoring the output on my scope, I notice the output waveform was heavily distorted when I switched to 4Ω and 16Ω load settings. It appeared like I was getting signal reflections, or my scope couldn't trigger correctly. I began to worry that my output transformer might be faulty or something...
                      Then I realized that I never took my scope prove off the 8Ω resistive load. Once that was corrected, all looked as it should.
                      -->Troubleshooting 101, often the problem can found between the bench and your shoes.

                      Edit: that should read “within 4% of each other”. I don’t think any of the equipment used to measure that has an error tolerance of .04%. I’d have to outsource this nevetslab to get that kind of accuracy
                      Last edited by SoulFetish; 01-17-2019, 05:55 PM.
                      If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

                      Comment

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