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SE-EL34 Design Help

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  • SE-EL34 Design Help

    I haven't been here for awhile. Things have changed! I've kind of taken an amp building break. But now I've got the urge to melt some solder!
    My next projext will be a SE-EL34 amp on a Tweed Deluxe chassis. It will have two channels; one voiced for single coils and one for buckers, single tone control. I plan to have the first stage followed by two more using the second AX7. This will feed an EL-34 and a Heyboer 18wt OT. The design concept is to get a pure EL-34 tone by hitting the tube pretty hard. So, I'm thinking a pretty robust power supply ,5AR4 with a 50/50uf filter cap.
    Here's my question: I'd like to go with a adjustable bias. I find the cathode bias to be a little primitive sounding (i.e. tweed tone). Virtually all SE amps seem to be cathode biased. So, there aren't many (any) schematics with an adjustable bias. I'm thinking that design wise I could just use a typical Fender/Marshall type bias and adapt it to the SE amp. Does anyone have any experience with this kind of amp design to share?
    Thanks

  • #2
    Bias is bias, just make sure things don't leave class A. Unless that is an effect you desire.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      You are on the right track with the bias. Just copy a Marshall circuit but you will probably need a lower (less negative) bias voltage.

      As for OT if the 18W you referred to is a push-pull unit I would not use it. The idle current will be too much. You need an OT designed for SE use. I used a Hammond 125FSE for an EL34 SE build.

      Aim for 300v on the plate and idle about 85mA and you will be good.

      DG

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