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  • Peavey Triumph PI hum/noise

    This amp is really pissing me off. Has a nasty hum and noise on all channels, preamp controls have no effect on it. The noise is kind of a whooshing sound (sometimes some pops) that does reduce after warming up but the hum stays the same. Plugging straight into the effects return it is still there.

    I have tried different PI tubes, there seems to be some effect on the hum/noise but it is always there.

    I have cleaned all the cable and jack contacts, as I know these are problematic on these amps. Moving wires around with wooden stick couldn't find anything that impacted the hum/noise.

    Pull all the preamp tubes other than the PI and the hum/noise is the same. Pull the PI tube and it is dead quiet. Replaced C42-C48 and C57, no effect. Unfortunately don't have high voltage probes for my scope to directly probe around the PI. Using the hum balance can change the noise but not really reduce it much, looking at speaker signal with scope shows that the hum balance can affect 60Hz hum but it seems like most of the audible hum is higher harmonics.

    I know that there is some sawtooth ripple on the -56V, even though C46 and 47 were replaced. I was surprised it didn't have hum in the 6L6 section just from that but I guess since it is common mode on a push-pull section it doesn't?

    Here is the schematic: https://www.thetubestore.com/lib/the...-Schematic.pdf

    Any thoughts on what to do next?

    Greg

  • #2
    Originally posted by glebert View Post
    This amp is really pissing me off. Has a nasty hum and noise on all channels, preamp controls have no effect on it. The noise is kind of a whooshing sound (sometimes some pops) that does reduce after warming up but the hum stays the same. Plugging straight into the effects return it is still there.

    I have tried different PI tubes, there seems to be some effect on the hum/noise but it is always there.

    I have cleaned all the cable and jack contacts, as I know these are problematic on these amps. Moving wires around with wooden stick couldn't find anything that impacted the hum/noise.

    Pull all the preamp tubes other than the PI and the hum/noise is the same. Pull the PI tube and it is dead quiet. Replaced C42-C48 and C57, no effect. Unfortunately don't have high voltage probes for my scope to directly probe around the PI. Using the hum balance can change the noise but not really reduce it much, looking at speaker signal with scope shows that the hum balance can affect 60Hz hum but it seems like most of the audible hum is higher harmonics.

    I know that there is some sawtooth ripple on the -56V, even though C46 and 47 were replaced. I was surprised it didn't have hum in the 6L6 section just from that but I guess since it is common mode on a push-pull section it doesn't?

    Here is the schematic: https://www.thetubestore.com/lib/the...-Schematic.pdf

    Any thoughts on what to do next?

    Greg
    i've used a .001 600v cap one end hooked and the other end clipped in the oscilloscope clip. The hook end would allow me to read in grab a socket connection with it being hooked I felt comfortable to look at the scope at that point.

    Pull and reseat all the molex connectors heck just clean them all.

    nosaj
    soldering stuff that's broken, breaking stuff that works, Yeah!

    Comment


    • #3
      Originally posted by nosaj View Post
      i've used a .001 600v cap one end hooked and the other end clipped in the oscilloscope clip. The hook end would allow me to read in grab a socket connection with it being hooked I felt comfortable to look at the scope at that point.

      nosaj
      on a scope how does the hum look?
      soldering stuff that's broken, breaking stuff that works, Yeah!

      Comment


      • #4
        Originally posted by nosaj View Post
        Pull and reseat all the molex connectors heck just clean them all.
        Did this first thing. No effect.

        on a scope how does the hum look?
        At the speaker? It varies with the hum balance, there is a 60Hz fundamental, which I can then dial out with the balance. As this is being reduced higher harmonics become visible and it starts to look very jagged. I don't have an FFT capability on my scope to see what specific frequencies are present.

        Comment


        • #5
          Originally posted by glebert View Post
          Did this first thing. No effect.



          At the speaker? It varies with the hum balance, there is a 60Hz fundamental, which I can then dial out with the balance. As this is being reduced higher harmonics become visible and it starts to look very jagged. I don't have an FFT capability on my scope to see what specific frequencies are present.
          Does what you see look different on a dummy load?
          Is the hum pot dirty ? It's evident the hum is before the pot or at it .
          ok if you leave it in standby and scope v5 pin 8 or 3 do you see the 60hz?

          nosaj
          soldering stuff that's broken, breaking stuff that works, Yeah!

          Comment


          • #6
            Originally posted by nosaj View Post
            Does what you see look different on a dummy load?
            Is the hum pot dirty ? It's evident the hum is before the pot or at it .
            ok if you leave it in standby and scope v5 pin 8 or 3 do you see the 60hz?

            nosaj
            Looking at the schematic and the location of the hum pot, I'd scope the filament lines then check c49 and c50 and the bridge rectifier

            nosaj
            soldering stuff that's broken, breaking stuff that works, Yeah!

            Comment


            • #7
              Originally posted by nosaj View Post
              Does what you see look different on a dummy load?
              Is the hum pot dirty ? It's evident the hum is before the pot or at it .
              ok if you leave it in standby and scope v5 pin 8 or 3 do you see the 60hz?

              nosaj
              Haven't used a dummy load yet. Hum pot didn't seem dirty (no pops or scratches when turning). I will check V5 at pins 8 and 3. Will also look at the heater filaments. I hadn't replaced C49 and C50 since I was thinking of those more as impacting V1-3, but I guess noise there would feed into the others through the balance pot.

              Comment


              • #8
                Originally posted by glebert View Post
                Haven't used a dummy load yet. Hum pot didn't seem dirty (no pops or scratches when turning). I will check V5 at pins 8 and 3. Will also look at the heater filaments. I hadn't replaced C49 and C50 since I was thinking of those more as impacting V1-3, but I guess noise there would feed into the others through the balance pot.
                yep that's what I was thinking after futzing around abit. since it disappears when you pull the PI.
                nosaj
                soldering stuff that's broken, breaking stuff that works, Yeah!

                Comment


                • #9
                  Screen resistors all good?
                  "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

                  Comment


                  • #10
                    Originally posted by The Dude View Post
                    Screen resistors all good?
                    Would a bad screen resistor quiet down with the PI pulled? I dunno just asking.

                    nosaj
                    soldering stuff that's broken, breaking stuff that works, Yeah!

                    Comment


                    • #11
                      I just finished up a Classic 30 with a hum problem (different amp, I know). Pulling the PI cut the hum almost all the way out, but still audible. Found an open screen resistor. Fixed.
                      "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

                      Comment


                      • #12
                        Originally posted by The Dude View Post
                        I just finished up a Classic 30 with a hum problem (different amp, I know). Pulling the PI cut the hum almost all the way out, but still audible. Found an open screen resistor. Fixed.
                        Good to know, from what i found this was Peavey's jcm800. Marshall even sent cease an desist letters suposedly. The Butcher was the other one.

                        nosaj
                        soldering stuff that's broken, breaking stuff that works, Yeah!

                        Comment


                        • #13
                          Correction: It was a Blues Junior, but still.......Those little tweed amps all look the same to me- that is until you peek under the hood.
                          "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

                          Comment


                          • #14
                            Originally posted by The Dude View Post
                            Correction: It was a Blues Junior, but still.......Those little tweed amps all look the same to me- that is until you peek under the hood.
                            Yea a classic 30 you'll never forget after having those folded boards connected with jumpers.

                            nosaj
                            soldering stuff that's broken, breaking stuff that works, Yeah!

                            Comment


                            • #15
                              Originally posted by The Dude View Post
                              Screen resistors all good?
                              I haven't even pulled the power tube board, this amp is like a house of cards with all the separate boards. The one benefit is not having to pull all the knobs and pot nuts to access the tube or power supply boards. Otherwise a complete PITA.

                              Comment

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