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5F2A with a 6L6 prebuild questions

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  • #31
    All great points MWJB

    I will follow your recommendations and rotate the 12ax7 , move the cap to shorten the grid wire to at 6l6, and install the 220k to ground at the tube. also shield the volume wire.

    This might take me some time, but I will get back with you.

    Thanks, Gerard


    • #32
      Thanks Guy's

      Thanks for all you suggestions! I rotated the 12ax7 which made me loose about 3" of wire, I installed a shielded wire from the volume pot to pin 7. rotated the .022 uf cap from the board to the 6l6 and installed the 220k to ground at the tube. No hum or oscillation at all, after the repairs!
      This amp is way louder than I expected! Almost at loud and my mission 5e3 but with a little less thump! That is what I was looking for. This thing screams with a blues driver in front of it.
      Now I need to build a cabinet! Thanks for all your help!


      • #33
        Build another amp and call it a 5F2A?

        I would stick with a NOS 5Y3FT and NOS 6V6GT tube, RCA 12AX7, Magnetic Components PT and OT and stock Fender schematic for this build.

        When built correctly in a tweed covered pine cabinet with 10" alnico speaker (yes alnico--try Magnavox 10" alnico) it sounds period correct.

        I have built several of these in the past and they sound fantastic. Measure your 470-ohm cathode bypass resistor and sometimes you need to substitute a 500-ohm or higher one if your bias voltage and current are too high--e.g. over 15 watts of peak power.

        Once you start changing tubes (stay away from solid state rectifier) you do not have a tweed princeton amp.

        Unless you want to "red plate" your 6V6 tubes or burn up your power transformer, there is no need to change this to a 6L6 based amp--build a 5E3 instead if you want more volume.

        Best regards,

        Dave Adams (a.k.a. "swaptronics")

        Originally posted by Gerard View Post
        Hi, I have just about all the parts on hand to build a 5f2a with a 6l6. I have some questions about the bias resistor and O.T. I will be running the 6l6 at about 400 volts with a 5y3 and about 450 volts with a gz34 recto. The P.T will handle the load of the tubes, so thats not an issue. What O.T would be a good choice? I had my eye on a Hammond 125ese 15 watt with 5k primary.Also should the bias resistor be a 5watt or 10watt at around 270R or so depending on the voltage? and should I raise the value of the filter caps , if so, what to values?

        Thanks again for your time. This is my third build, my first one was a Mission 5e3 that I kept stock and love the sound. This forum has been a great help to me over the past years and I appreciate all the help.