EL84 With A 5F4 Circuit

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

  1. Stephen Bell

    Stephen Bell NEW MEMBER!

    Dec 27, 2010
    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

    Oct 3, 2010
    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

    Mar 17, 2003
    Lubbock, TX
    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.
    Mr Ridesglide likes this.
  4. printer2

    printer2 Poster Extraordinaire

    May 24, 2010
    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

    Apr 4, 2015
    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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