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O/P Transformer Change. Rebias?

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  • O/P Transformer Change. Rebias?

    Hope I've got the right forum for this question. Earlier this year I built a 5E3 circuit with JJ 6V6 tubes. However I used an output tranny meant for 6L6's.
    Amp is fine, but I need this tranny for a new build, so I'll get a proper 6V6 deluxe tranny to go in the 5E3. Question is, will I need to rebias? I'm guessing the tubes will see a different load? I will also have to change the speaker from a 16 Ohm to an 8 Ohm.

  • #2
    The power tubes may see a slightly different OT primary DC resistance when idling, but that wouldn’t affect the idle current very much. The AC load reflected by the OT back to the tubes, from the speaker, should be more suitable for the 5E3 circuit.
    Also, the 5E3 is cathode-biased, so it should self-adjust to a large extent. I'm assuming you have the 250 ohm shared power tube cathode resistor shown in the schematic:
    Having said all that, after major surgery like a new OT, it would be good idea to check things anyway.
    Last edited by Malcolm Irving; 07-14-2016, 09:38 AM.