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Orange AD200B Mk II Bass Amp

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  • #16
    Originally posted by Bernardduur View Post
    As for the MKIII

    1. I'll check back when I biased her correctly!

    2. 474 VAC and 267 VAC

    3. Woops; I'll correct that!

    4. They are 3mm LED's. They'll light when a fuse is down
    Could you tell me, was the 474 VAC and 267VAC on load? i.e. not on standby.

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    • #17
      Originally posted by TDS View Post
      Could you tell me, was the 474 VAC and 267VAC on load? i.e. not on standby.
      Yep; on load!

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      • #18
        Bernardduur, thanks for the schematics!

        I'm trying to rebias an AD200 Mk3, too. I have read the thread but I didn't understand the part with the fuses...

        I installed a new set of SED 6550 and 4 1Ohm resistors where the PCB says 1Ohm to measure cathode current at each tube. Do I have to take off the fuses or something like that? Or my measurements across the 1Ohm resistors will be correct?
        With the trimmer set fully biased my maximum readings are 20mA per tube! That's Ice Cold as TDS said.

        If I install a 68K resistor in parallel with the stock 68K at the bias circuit will I have the advantage to bias the tubes hotter?

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        • #19
          Originally posted by spy View Post
          Bernardduur, thanks for the schematics!

          I'm trying to rebias an AD200 Mk3, too. I have read the thread but I didn't understand the part with the fuses...

          I installed a new set of SED 6550 and 4 1Ohm resistors where the PCB says 1Ohm to measure cathode current at each tube. Do I have to take off the fuses or something like that? Or my measurements across the 1Ohm resistors will be correct?
          With the trimmer set fully biased my maximum readings are 20mA per tube! That's Ice Cold as TDS said.

          If I install a 68K resistor in parallel with the stock 68K at the bias circuit will I have the advantage to bias the tubes hotter?
          I wired the fuses completely out of the circuit as they were giving the kathode an unstable current. The fuse resistance varied with temperature and load.

          Now, with the 1 ohms to ground directly I got good readings from the tubes.

          With the 68k parallel I got her to fully functioning and MUCH better sounding!

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          • #20
            Hey guys, from the schematics provided by Bernardduur would it be possible to build the ad200b mk3??

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            • #21
              Greetings, Folks! I'm a newbie in the forum, but have been following the thread for some time. Having the same interest in building my own ad 200, with sufficient-tons of info I get here, it's time to join in :grin: Again thanks to bernard!

              I'm planning to replace the power tubes to 3 pairs of EL 36s, as described by Mr. Chambers on his ridicoulously high-powered amps, 12 EL 36s are able to pull 500+ watts of power, so I figured 6 of them would do half of it, which is more than I need..

              Cheers..
              Last edited by tubesfreak; 04-08-2012, 06:21 PM.

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              • #22
                Does anybody still have a working link for schematics on the MkIII? I have one with KT88's installed, and R26 looks like it got crispy hot. It's color coded as a 3.9k, but measures around 4.2k ohms. Also 2 of the 1K ohms resistors going to the grids seem to have drifted down to around 970 ohms. It came in with lots of noise on the output. Any help is much appreciated 😊

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                • #23
                  Here are the unofficial schematics that used to be located at the non functioning Photobucket-link above:





                  I did'nt seem to find R26 and I don't know how accurate the designations are on these schematics. It's a fairly simple construction so you might find your way anyhow. I have the official schematics on my homecomputer (I'm at work now) if needed.

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                  • #24
                    Nice! Thanks. I am still not seeing a 3.9k resistor in the power supply, but these are the pre and power amp schematics I found, and there are major discrepancies between it and the model i am working on. Let me know if you see one on the original schematic

                    Thanks again,
                    Jason

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                    • #25
                      It's been a busy weekend so kind of late posting, sorry. The resolution of these original schematics are really lousy to say the least, but they're all I've got:



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