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Marshall Artist, extremely low volume output.

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  • Marshall Artist, extremely low volume output.

    Hi, I have an old 80s Marshall Artist, 30 watts, 2 EL34s. The amp had worked fine for a number of months but now it has a super low output. I have determined the preamp section works fine because I ran the effects send to another amp. Both channels operated as they should. I substituted the phase inverter and the power tubes from another working amp and the problem persists. Here are the voltages from the power tubes:
    V2 V3
    P3 488V 489V
    P4 486V 487V
    P5 -49V -49V
    P6 488V 488V

    Any assistance would be appreciated.

  • #2
    Have you tried a cable between FX send and return?
    It's weird, because it WAS working fine.....

    Comment


    • #3
      Yes. Doesn't change anything.

      Comment


      • #4
        Anyone else think that bias voltage on pin 5 is a bit too negative for EL34's?

        Comment


        • #5
          Originally posted by mfreqmaster View Post
          Hi, I have an old 80s Marshall Artist, 30 watts, 2 EL34s. The amp had worked fine for a number of months but now it has a super low output. I have determined the preamp section works fine because I ran the effects send to another amp. Both channels operated as they should. I substituted the phase inverter and the power tubes from another working amp and the problem persists. Here are the voltages from the power tubes:
          V2 V3
          P3 488V 489V
          P4 486V 487V
          P5 -49V -49V
          P6 488V 488V

          Any assistance would be appreciated.
          please report also the PI tube voltages
          you also have a couple of opamps in line from the return jack to the tube,it could be some failure or simply a fractured soldering.

          Comment


          • #6
            Originally posted by m1989jmp View Post
            Anyone else think that bias voltage on pin 5 is a bit too negative for EL34's?
            i'd say to turn off an el34 you must go up to -80V

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            • #7
              PI voltages: p1 434v, p2 7v, p3 31.5v, p6 221v, p7 18.5v, p8 31.5v

              Comment


              • #8
                Originally posted by mfreqmaster View Post
                PI voltages: p1 434v, p2 7v, p3 31.5v, p6 221v, p7 18.5v, p8 31.5v
                The resistor connected to pin 1 is most probably shorted,once replaced the voltage will be similar to pin 6

                Comment


                • #9
                  I suspected that too, but measured and it is 87k ohms. I will check the solder joint to that pin next.

                  Comment


                  • #10
                    Originally posted by mfreqmaster View Post
                    I suspected that too, but measured and it is 87k ohms. I will check the solder joint to that pin next.
                    reflow also pin3

                    Comment


                    • #11
                      Are both sides heater lit at PI tube position?
                      "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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                      • #12
                        I'm with g1, it is most likely the pin 1 side of the tube is not conducting, usually because the heater is not lit.

                        I have never in my life seen a shorted resistor.
                        Education is what you're left with after you have forgotten what you have learned.

                        Comment


                        • #13
                          Originally posted by Enzo View Post
                          ......I have never in my life seen a shorted resistor.
                          Ditto!
                          "Yeah, well, you know, that's just, like, your opinion, man."

                          Comment


                          • #14
                            Me three. Although I did see one once that had decreased substantially in resistance. So I never say never about that anymore.
                            Although I still never expect to see a complete short.
                            "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                            Comment


                            • #15
                              The only time I've come close was when I measured a 100K resistor and it measured 10K. It was while teching at a manufacturing facility. After encountering the same part problem several times, we checked the batch. It turns out the manufacturer marked a batch of resistors wrong. Still,...... they didn't short- I don't recall ever seeing a shorted resistor.
                              "Yeah, well, you know, that's just, like, your opinion, man."

                              Comment

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