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Noob modding a PA/Phono amp?

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  • #1

    Noob modding a PA/Phono amp?

    Okay, right off the bat, I'm a noob at tubes. Built a few small SS 'practice' amps, but nothing with tubes. I have worked with high voltage before (AC mostly, in my past as a 'spark-trician') so I know about electrical safety. Yes, I understand that the circuits can 'store' some energy so they need to be bled down.

    But I've aquired a small PA/phono amp (it has two inputs) to use as a Frankenstein learning project. I know I need to replace at least one pot as it is bad (it serves as the on/off switch as well as the tone control of all things). But the tubes it uses are 12AX7 (pre-amp, split to pre amp each of the inputs separately), 6AQ5 (which I believe is similar to the 6V6), and a 6X4 (I think this is the rectifier). So it has a bit of potential by using both stages of the 12AX7 to be a bit 'Champy'. Main issue is the power tranny. I believe it only puts out 250V, so to replicate a circuit like a 5E3 (or even an AA764) I believe I'd need to recalculate the resistor values or change the tranny.

    But my objective is to take a small step into the pool and learn the circuit. So, could this thing work (function, but not have to sound like a Champ, but be passable for my extremely limited playing ability)? Comments? Suggestions? Flames?
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  • #2
    The whole point of converting something to me is to use it in teh process. To get more voltage from the power transformer would be to replace it, or maybe wire in a voltage doubler. Otherwise you have a piece of metaql with some sockets.

    Try making an amp using that 250v. After all, it amplified the phono at one point, didn't it. SO it won't be a pair of 6V6s in a 5E3. Circuits are circuits, and they all work about the same way. You will learn about amps just as well with any amp project.

    In other words, don't worry about what it isn't, think about what it can be with what it IS.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      http://www.ampwares.com/ffg/schem/champ_5f1_schem.gif


      http://www.schematicheaven.com/barga...supro_1959.pdf

      http://www.schematicheaven.com/barga...oo_model-1.pdf

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      • #4
        Well, the amp isn't exactly working right now. Need to replace a pot to start with.

        Thanks Satamax, those schematics help.

        I'm really just wanting to use this thing to learn how to bias tubes and all. Then I'll look into something serious.

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        • #5
          BTW,
          You can probably use your existing PT for the amps that Satamax gave links for, but *probably* not for a 5E3 or anything with more tubes, since they will draw more current than the transformer was desinged for.

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          • #6
            That's what I was considering. I like that Supro schematic so I'll try to work that this weekend. Wanted to finish my Flying V first.

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