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Beginner project: Heathkit A7 into guitar amp

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  • #31
    Originally posted by G-hoppa View Post
    Loudthud-- I notice on this you've changed the B+ for the 12SL7 from 180V to 330V. Is this the mod you made to enable the use of a GZ34? Since I'm going to keep the 5Y3, can I simply use the original 100K resistor there at the last filter cap?

    What would such a large voltage difference have done to the gain and tone of the 12SL7?
    The original amp was intended to amplify a phono cartridge. Those signals are much smaller than a guitar signal. A higher B+ will increase headroom. The lower B+ would work good for a harp amp though. For a GZ34 you just need to take the output from pin 8 instead of pin 2 like the original.
    WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
    REMEMBER: Everybody knows that smokin' ain't allowed in school !


    • #32
      The sweet sound of success!

      Thanks to all who helped with suggestions. I finally got the Heath A-7E finished and played through it with the band last night-- better than I could've hoped. It's not just a working guitar amp-- it sounds fantastic! Crunchy, tight,--better than my current Peavey Classic 30. (granted, it has a smaller range of sounds to dial in than the Peavey, but I tend to play with a particular sound, and this Heath does it better) I have yet to build a head box for it, and one of the NOS tubes (6SL7GT) is microphonic, but all in all, an encouraging first build.

      Now I need to dig into the old Bell hi-fi I have and create another. It's addictive.



      • #33
        Congrats! I'd love to hear how this turned out, I can sort of visualize it.

        I ran into some stumbling blocks on my Heathkit conversion and some other things in life have forced me to put it on hold for the last month. Hope to get back to it in a week or so.


        • #34
          Source for A7 build manual

          Sorry to bump this thread - but I have just acquired a Heath A7(E) and would like to know the source for the build manual you mention - or would be willing to pay the cost to ship a copy. Also would be interested in anymore you would have to say for another soul following your path. thx much!


          • #35
            Somebody brought me one of those last Friday and wanted it modded for guitar.

            Here's what I ended up doing...

            Click image for larger version

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