HometechnicalOutput transformers and push-pull stages. Part 2


Output transformers and push-pull stages. Part 2 — 2 Comments

  1. Thanks for explaining how an output transformer has no impedance in itself. My friend is thinking of purchasing an output transformer. I’ll tell my friend about how output transformers have no impedance so he can be prepared for that when he buys one.

    • Hi, and thank you for commenting.
      It is the transformer ratio that gives you the needed primary impedance and the correct load for the valves, not the transformer primary in itself. The transformer you linked to has 8 k. ohms primary impedance if you use an 8 ohm load to the secondary side. So the ratio for this transformer is then:
      n = √(Primary Impedance(R1)/Secondary load(R2)) = √8000/8 = 31.62

      If you instead connected a 4 ohm speaker to the same transformer the load presented to the valves would be:
      Primary impedance = (n) ² x secondary load => (31.62) ² x 4 = 3999 ohm, using the same transformer.

      This is why we say that a transformer has no impedance of itself, it only reflects the secondary load impedance over to the primary side by the transformer ratio².

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