EL84 With A 5F4 Circuit

Discussion in 'Amp Tech Center' started by Stephen Bell, May 24, 2019.

  1. Stephen Bell

    Stephen Bell NEW MEMBER!

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    Has anyone one out there tried to anything like this? 4 El84’s as the power supply and blending the 5F4 circuit together. If so, I would appreciate some good advice so this project will be successful.
     
  2. AJBaker

    AJBaker Friend of Leo's

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    I can't help, but I look forward to seeing how it turns out!
    What's the desired outcome? Do you want to blend a tweed/vox vibe? Do you want the possibility of getting half power by turning off two of the output tubes?
    In theory, combining a 5f4 pre amp and something like an AC30 endstage should be possible. I see a few things to work out:

    What kind of phase inverter? A vox is long tail pair (more gain), and I think a 5f4 is cathodine (less gain).

    Fixed bias or cathode bias? A vox is cathode biased, and a peavey would be an example of a fixed bias 4x el84 setup.
     
  3. Wally

    Wally Telefied Ad Free Member

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    Welcome, Stephen.
    The preamp in the Fender Blues Jr. is related to that tweed preamp...2 gain stages prior to a tone stack. One difference is that the Super uses a cathode follower to drive the tone stack. Another difference is that the Blues Jr. uses a longtail pair PI versus the cathodyne PI in the 5F4, so that puts the Blues Jr. more in the 5F6A camp. The Blues jJr. Uses a hot fixed bias output section...too hot imho but that is another subject.
    For my money, I would simply build the 5F4 as it is. Ommv.....but tube choice is not as important as circuit choice, Ime.
    But...this question brings to mind that beautiful power tranny that I have from a Sherwood stereo...4xEL84’s and plenty of ‘room’ for any preamp.
     
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  4. printer2

    printer2 Poster Extraordinaire

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    Both LTP and Cathodyne have been used with 6V6's and EL84's, I don't think the tubes will mind if you do it.
     
  5. clintj

    clintj Friend of Leo's

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    Only thing I see is the EL84 is just a little more sensitive/easier to fully drive than a 6V6 and has a lower set of max allowable voltages as far as screen and plate, but it should be fine. Tweeds are low enough gain that it should work pretty well.

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