Power transformer secondary taps

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by CubanB, May 6, 2015.

  1. CubanB

    CubanB Member

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    If you have 6.3V filament or 300V B+ taps coming out of a power transformer that isn't center tapped, does it matter if the two leads are reversed, or are they both the same?

    I know that with output transformer you have the center tap that goes onto the B+ and then the other two leads go to the plate supply of each power tube. And if the two leads are reversed the amp will squeal and you will need to reverse them but what about on the AC power transformer side, when there is no center tap?

    Can you use the two leads either way without issue, or will there be an issue and how do you identify which is the correct way?

    Cheers
     
  2. xtian

    xtian Member

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    No difference.

    The polarity of OT secondaries are only an issue when you have negative feedback.
     
  3. CubanB

    CubanB Member

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    Makes sense, thanks.
     
  4. PushedGlass

    PushedGlass Member

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    And that can be an issue whenever you're replacing an OT with anything but make/model stock because there seems to be no real convention about secondary/primary polarity even when the lead colors match. I replaced an original '78 Fender Princeton Reverb with a multitap Hammond OT meant for a Deluxe Reverb and it went crazy with feedback, the negative feedback loop (a line with a series 2.7K resistor running from the OT secondary to the PI stage) having been turned positive. Swapped wires; problem solved.
     

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