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  • Orange noise

    I have a AD 200 bass mk 3 here with a loud buzz. I can kill it with the MV and by pulling v2 or v3 . The only scem i can find is on prowess amps but its not correct to this amp. This pcb is dated 2006. (ill try calling Orange tomorrow) , I tried clipping in a 50uf filter cap at all the plates v1/2/3 - it doesnt affect the noise unless i clip it to the plates of V1--but then i have almost no volume .

    i did find about 18 vdc at the grids of V2 -- that shouldnt be there, yes ?

    the shielded cable grounds are good




    side note = theres a cap in here , that i think is a coupling ( traces are on both sides of pcb-cant see the bottom) , but its got strange labeling. Can someone decipher this ?

    R60 MKT 400 A9 10MRL19

  • #2
    You found 18V at the grids, what was at the cathodes and plates?
    How about a pic of that component with the marking.
    Originally posted by Enzo
    I have a sign in my shop that says, "Never think up reasons not to check something."


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    • #3
      Probably a version of these.

      https://www.surplussales.com/capacit...s/R60-MKT.html

      Datasheet with marking system.

      https://www.surplussales.com/capacit...ne/pdf/R60.pdf
      "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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      • #4
        Originally posted by g1 View Post
        You found 18V at the grids, what was at the cathodes and plates?
        How about a pic of that component with the marking.
        pin 3 33vdc
        pin 8 33vdc
        pin1 202vdc
        pin 6 198vdc

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        • #5
          With the cathodes at 33V, the 18V at the grids is not necessarily a problem.
          Without some kind of schematic, even close, it's all guesswork as far as hum.
          Sometimes there are DC heaters for the early preamp stages. See if you can find out if there are AC or DC heaters on the preamp tubes.
          Originally posted by Enzo
          I have a sign in my shop that says, "Never think up reasons not to check something."


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          • #6
            all heaters are AC --all tubes

            orange wont send me a scem. any authorized guys on here ?


            heres a vid of the noise =

            https://vimeo.com/259402089

            edit---the amp owner knows a rep there , so hes trying to get me the scem.
            Last edited by Valvehead; 03-09-2018, 11:12 PM.

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            • #7
              It's obvious, but have you tried a new 12AX7? Sometimes I have seen that noise (with more bass component) in defective tubes. Specifically in ECC83 JJ and Tesla E83CC (same type of construction).

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              • #8
                yep--swapped out every tube.

                i cant get directly to the filter caps-they are vertical pcb and some of the traces are on the bottom .. so i clipped in a 50uf at all the plates of the preamp tubes. Would that cover it , or do i need to get directly to some of the caps "first in line" ? if that makes sense

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                • #9
                  Ok, your funny voltages look like they are on a LTP phase inverter. The plate voltages are close, the cathodes are the same. probably wired together, and the grids have the DC the cathode has, but your meter cannot read it due to the high resistances. Looks normal then. Instead of measuring pins 2 and 7 to ground, try measuring 2 to 3 and 7 to 8. I bet you only get a volt or two.

                  You can't tack a filter cap on the tube plates, that acts like a giant tone control rolling off your audio.

                  Pulling V1 stops the noise? Pins 2 and 7 are grids. Try grounding each of those one at a time. Either kill the hum?
                  Education is what you're left with after you have forgotten what you have learned.

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                  • #10
                    .........

                    Originally posted by Enzo View Post
                    Ok, your funny voltages look like they are on a LTP phase inverter. The plate voltages are close, the cathodes are the same. probably wired together, and the grids have the DC the cathode has, but your meter cannot read it due to the high resistances. Looks normal then. Instead of measuring pins 2 and 7 to ground, try measuring 2 to 3 and 7 to 8. I bet you only get a volt or two.


                    YES--THATS WHAT I SEE


                    You can't tack a filter cap on the tube plates, that acts like a giant tone control rolling off your audio.

                    Pulling V1 stops the noise?


                    NO--PULLING V2 /3 KILLS THE BUZZ

                    Pins 2 and 7 are grids. Try grounding each of those one at a time. Either kill the hum?

                    ON V1-- GROUNDING GRIDS -- 2. NO STILL HAS LOUD BUZZ 7. KILLS VOLUME-- STILL BUZZ IN BACKGROUND / QUIETER

                    V2-- 2. KILLS BUZZ 7.KILLS VOLUME, STILL BUZZ IN BACKGROUND / QUIETER

                    V3 2. KILLS BUZZ 7. KILLS VOLUME , BUZZ STILL IN BACKGROUND -QUIETER

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                    • #11
                      I'm thinking you are experiencing an imbalance somewhere in the phase splitting circuit?

                      Here you have some unofficial schematics:



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                      • #12
                        i think i have found the correct scems.....pm me for link

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                        • #13
                          Try measuring heater (ac) voltage on preamp tubes, ground to pins 4/5 and ground to pin 9. They both should be around 3.15V AC

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                          • #14
                            3.89vac

                            3.34 vac

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                            • #15
                              You said you can kill the buzz with the master. That leaves only V1 ahead of it so you can concentrate on that area.
                              How about with the gain all the way down, does the master still bring the buzz in and out?
                              Originally posted by Enzo
                              I have a sign in my shop that says, "Never think up reasons not to check something."


                              Comment

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