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Are these schematics the same?

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  • Are these schematics the same?

    If this post is in the wrong spot I apologize. This is my first post here and I wasn't 100% sure which sub forum I needed. Anyways...

    The title says it all. The two schematics in question are an undated Orange OR120, and another Orange OR120, dated 1972. I'm able to read the schematic enough to tell they're very similar, but am not advanced enough to figure out if they're really different. If they are different, is it safe to say the undated schematic is an earlier version? I'm looking to have a clone built with a few mods and would prefer the earliest version so I can get as close as possible to a Matamp (since schematics for those are hard to find).

    I also have one smaller question regarding the first schematic. For capacitors 10, 12, 13, 14, 16, 17, 18, 19, 20, and 21, are they in uF? My glasses are currently smashed and the handwriting is small and not very neat. It almost looks like nF but that seems kind of odd, so I figured I'd ask and be sure.

    Thanks in advance!

  • #2
    No, they are not the same. They are very similar.

    Your list of caps are all in picofarads.

    The main differences that leap out at me are the boost circuit in the one is just a cathode bypass cap setting, while on the other it is an LC circuit in local feedback. Also, in ine the phase inverter is direct coupled to the boost stage, while in the 1972 one the phase inverter is now self biased and cap coupled to the previous stage. And also the bias power supply is full wave rectified in 1972, though the ground is missing there. The other is typical half wave but is adjustable. Though they do take bias from a pot wiper, which is a nono to me.

    Were it mine, I'd decide on the bias supply by what transformer windings you have. I would make it adjustable, but would also change it to not coming off a pot wiper. personally I'd prefer the PI with the coupling cap.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      Hi SMB13

      You may find this helpful. It's a clone of an 80 looks similar except only has 2 o/p tubes.

      freestompboxes.org ? View topic - Orange OR80 Style Build

      and Welcome to the Forum

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      • #4
        Okay, awesome. Thanks guys!

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