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EL84 power amp design

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  • EL84 power amp design

    My browser crashed and I lost the whole post I just typed. Don't feel like typing the whole entertaining back story. So here's the meat of the post:

    I am currently running my pedalboard thru my Fender M80 clean channel or FX return. Either way, sounds satisfactory. Sounds WAY better than my ValveJR (my only tube amp, and its got the stock OT). Pushed with my Jekyll and Hyde Analogman Fuzz the JR is more farty than grandpa after two black bean burritos. Ok. I slipped in one joke.

    I want to build a SE EL84 power amp, or an 18w PP EL84 power amp. The point is this- I like the tone I get at my front end and don't need a big fat cascading preamp for distortion. As a matter of fact, I wish I could just add some output tube and transformer tone and be done with it. MY PROBLEM:

    I have schematics out the wazoo of output sections and even a few of dedicated power amps. My question is this- how are things set up so that I don't introduce distortion from the driver tube, and still drive the output section to some sweet distortion? Really, I can't see a major difference between the Valve JR schematic and the 5-7w EL84 power amp schematic I got from ..?musicman?.
    See where I'm going with this? From what I'm looking at, the 'power amp' with its 12AX7 looks just a 'guitar amp' with a 12AX7 preamp! Ugh.

    The same question would apply to the 2x EL84 power amp I'm thinking of doing. If I do the power amp with one EL84, I'm going to run it to a Weber attenuator with the fake speaker and amplifiy it thru a big fat power amp I have. I guess that would make it an 'output tube effect', really. But since I'm playing out, I'd most likely go with the 18w power amp. I want some sweet output tube tone.

    Thanks!
    Jeff
    Last edited by zikaj; 05-18-2007, 03:56 AM.
    www.myMANICEPISODE.com

  • #2
    Take a look at this project from Hoffman amps:

    http://www.el34world.com/projects/StereoPowerAmp1.htm

    Stereo EL84 power amp only.

    steve

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    • #3
      Thanks Steve.
      Turns out I had printed this schematic a while ago and didn't flag where I saw it. So a bit thanks, really. This is exactly what I am looking for.

      Since I'm doing this as a DIY build, I'd like to use it to learn/fill in the gaps of my understanding ("theory and design" seemed a good place to do this. Sorry if I'm asking a dumb Q).
      The 1M pot at input controls the signal hitting the driver tube, the driver tube drives the PI and output. Got it. I can only think about this in guitar amp terms, and can't get past how this set up overdrives the power tubes, but doesn't add distortion from the driver. I'm thinking its going to be a matter of a lower gain tube in the driver, and what the voltage is on the plates. Or, because you only hit one (half) of a tube, you don't get a huge gain factor. That, actually, sounds more like it.

      Thanks!
      www.myMANICEPISODE.com

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