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Build 5E4-A (6v6 tweed super) with 5e3 transformers?

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  • Build 5E4-A (6v6 tweed super) with 5e3 transformers?

    I've got some Mercury Magnetics transformers I intended for a 5E3. Now I want a 2x10 speaker arrangement.

    Can I use those transformers for a 5E-4A (6v6 tweed super) if I switch the rectifier tube to a 5Y3 instead of a GZ34? The power transformer has a B+ center tap. Also, any problem with adding a cathode/fixed bias switch?

  • #2
    Use 2x16ohm speakers in parallel to get 8ohms overall.

    The rectifier you use won't worry the PT, it might put out too much voltage for the power tubes if you use NOS (EH/JJ will take the extra voltage no problem).

    No problem with a cathode/fixed switch, draws no current, tap the bias supply from one of the PT wires to pin 4 or 6 at the rectifier, like a Marshall JTM?

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    • #3
      How can I reduce the current to the 6V6 power tubes, if I need to?

      I understand that the 5E4-A ran too hot and that is part of the reason for the switch to 6L6 tubes with the 5F4. I thought the 5E3 transformers may help with that problem, but I don't really know. If I need to reduce the power tube voltage, how can I do that?

      Thanks for the help

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      • #4
        The tubes won't run any hotter in a 5E4A circuit than in a 5E3, just a little more heater voltage needed for the 3rd 12A?7 in the 5E4A design...a 2A 6.3VAC winding should cope fine with 2x6V6 & 3x12A?7.

        Decrease plate voltage with a NOS 5Y3 if necessary, or increase plate current if you have scope to do that, alternatively a reverse polarity Zener diode can drop anything from 5-50vdc off your final plate voltage...build it first see what you get with rectifier of your choice (5Y3/5V4?) & appropriate plate current. Tolex Princetons & Deluxes run up to the mid 400's with modern 6V6 if you want a datum.

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        • #5
          Thanks again

          I need all the help I can get. As I read my own question, I can see that I mixed up voltage and current. I'll get it straight.

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          • #6
            All you need to do is build this with an adjustable bias supply, as found on a black or silver face Deluxe Reverb and ground the cathodes of the power tubes.
            You can use what ever rectifier you want.
            I don't know how much power you are going for but I can tell you that the 5E3 transformers and a fixed bias pair of power tubes will net you around 18-20 watts output all day long.
            If you are trying to get solid power then use the GZ34/5AR4 and set the power tubes to idle around 9-10 watts each but if you go cathode biased with a switch then you will want to use a 360 ohm power resistor for the cathode biasing resistor instead of the traditional 250 to 270 ohm one.
            There are lots of layouts for this fixed-cathode biasing mod.
            I have built a few 5F4 amps with 6V6s (cathode and fixed bias [switching and non-switching bias]) and yours would be a very similar project.
            Bruce

            Mission Amps
            Denver, CO. 80022
            www.missionamps.com
            303-955-2412

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