Announcement

Collapse
No announcement yet.

Peavy 5150 II - crackle and pop amp noise

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Peavy 5150 II - crackle and pop amp noise

    Hey everyone,
    I'm looking for some help on an amp i've been troubleshooting for a few months now.
    I have a Peavey 5150 Mark II that is making intermittent crackles and pops.
    Crackle is happening with old tubes and complete new set of power and preamp tubes.
    The noise is in both channels.

    If you remove V3 (effects tube) the crackling stops

    Here's the schematic i'm working off of.
    https://www.thetubestore.com/lib/the...-Schematic.pdf

    I've been going down rabbit holes and nothing i've conducted has made the problem better or worse.
    My next guess is a noisy coupling cap that's causing the issue but i'm shooting in the dark at this point.

    Here is a list of the work I have done so far and why:
    1) Replaced C34, C35, C38, C39, C44, and C46 filter caps. (Slightly bulging and they tested leaky)
    2) Replaced R205 screen grid resistor (open)
    3) Replaced C159, C9, C164, C163 electrolytics (caps blew)
    4) Shotgun replaced all plate resistors on preamp board (I thought a noisy resistor was the issue - no change)
    5) Replaced R5, C11, R26, R85, C158, R14 coming off V3A effects tube
    6) Replaced all preamp tube sockets with new beltons. (contact pins on old sockets were in poor condition and couldn't be retensioned)
    7) Bypassed the effects loop board completely to rule out any faulty resistors or transistors that may be on that board (no change)

    Any help is appreciated.
    thanks,

  • #2
    Correct me if I am wrong but V3 appears to be the Phase Inverter tube.

    Have you tried running a patch cord in the FX loop jacks?

    Try to narrow down the issue to the preamp or the power amp.
    Using the FX Send, send the preamp signal to another amplifier.
    Likewise, send another amplifier (or plug in your guitar) to the FX Return jack, which goes directly into the power amp.

    Here is a copy of the schematic.
    Peavey-5150-II-Schematic.pdf
    I could not rotate the link that you used.

    Comment


    • #3
      Oh my...

      First the small tubes have series wired heaters, so you CANNOT pull one of them without others going off as well.


      Next, what are you calling V3? Looking at the rear of the amp, the small tube numbers are in this order: V6-1-2-5-3-4 They are NOT in order across the row.


      Isolate the problem, WHERE in the amp is the noise? Before or after the loop jacks? Does ANY control affect the noise in ANY way?
      Education is what you're left with after you have forgotten what you have learned.

      Comment


      • #4
        V4 is the Phase Inverter tube (to add confusion they labelled the plate voltage V3+). Like Enzo said the filaments are wired in series, so when you pull V3 then V6 goes down. The same with V1 and V2, pull either and the other goes down. Where and how did you bypass the effects board (do you mean the "breakaway" in the schematics)? That board is already bypassed by relay K3 when the effects loop is disengaged. When you switch the effects loop in and out is there any difference? If you bypassed the relay and breakaway board to no effect you might check for DC leakage from C52 in front of V3B.
        Last edited by doombass; 05-14-2019, 10:58 AM.

        Comment


        • #5
          Originally posted by Jazz P Bass View Post
          Correct me if I am wrong but V3 appears to be the Phase Inverter tube.

          Have you tried running a patch cord in the FX loop jacks?

          Try to narrow down the issue to the preamp or the power amp.
          Yes, I tried running a patch cable into the effects loop awhile ago but it didn't make a difference. I'll try using the FX send into another amp and see what happens. I thought I had isolated the problem but I wasn't aware the preamp filaments were wired in series, now i'm back to square one. As for bypassing the effects board, I disconnected the individual ribbon connectors. I'll start with your recommended suggestions and go from there.

          Enzo,
          - V3 next to V4 (phase inverter)
          - No knob affects the noise


          thanks,

          Comment


          • #6
            Yes K3 contacts might be bad.

            Comment


            • #7
              Yes, I tried running a patch cable into the effects loop awhile ago but it didn't make a difference.
              You mean you put a signal into the FX return and the noise remained? That would mean the noise was in the power amp or power supply.
              Education is what you're left with after you have forgotten what you have learned.

              Comment


              • #8
                The way I see it, logically (like amp problems are always logical ) the problem is kind of narrowed down. It concerns both channels and disappear when V3 is pulled. V6 (clean channel preamp) goes down with V3 but V6 has already been checked by altering channels. Effects loop board has been both disconnected and looped with patch cable. I presume you used the effects loop in/out switching when testing this so we can rule out contacts on relay K3. Logically the crackle appears between terminal 7 of channel switching relay K28 and control grid pin 2 of V3A. Or is my logic off?

                Comment


                • #9
                  Just to be sure about K3, I swapped K3 with K2, they are the same relay and this made no difference. I'm going to send the signal out from the effects loop into another amp and vice-versa tonight, I'll report back. I think your logic is in the ballpark though!

                  Comment


                  • #10
                    Originally posted by Enzo View Post
                    You mean you put a signal into the FX return and the noise remained? That would mean the noise was in the power amp or power supply.
                    Yes, putting a signal into the FX return the noise remained.
                    Sending the signal into another amp - the noise was gone.

                    Comment


                    • #11
                      So clearly the noise is coming from after the FX return. SO one V3 triode circuit and the phase inverter or the power tubes. Not saying it is a tube, but in the tube circuits. Like noisy resistor.

                      So I don't recall, did the noise go away with pulling V4? You can pull V4, but not the other small tubes.
                      Education is what you're left with after you have forgotten what you have learned.

                      Comment


                      • #12
                        Originally posted by Enzo View Post
                        So clearly the noise is coming from after the FX return. SO one V3 triode circuit and the phase inverter or the power tubes. Not saying it is a tube, but in the tube circuits. Like noisy resistor.

                        So I don't recall, did the noise go away with pulling V4? You can pull V4, but not the other small tubes.
                        Pulling V4 causes the noise to stop as well.
                        Just to restate... ALL tubes are brand new sovteks. I also put in a quad of known good JJ power tubes and the noise was still there.
                        The power amp board is riveted to the chassis, I had previously removed it to replace a screen grid resistor. While doing that I inspected the board and I noticed some dirty solder connections.
                        Since the board was already out, I cleaned and re-flowed all the power tube sockets and other affected connections - still no change.

                        Now that we have the area narrowed down... how else can I troubleshoot a single faulty component? chop sticking doesn't seem to influence the noise.
                        At this point do I just shotgun replace suspected components like noisy resistors?
                        My troubleshooting abilities are limited by my knowledge, i'm fairly new to amplifiers.

                        Comment


                        • #13
                          OK, so the problem is now either before or AT V4.

                          Look at grid pin 7 and R48 of V4. See PREOUT nearby? That connects to the Preamp Out jack. SO, is the noise present there?
                          Education is what you're left with after you have forgotten what you have learned.

                          Comment


                          • #14
                            Originally posted by Enzo View Post
                            OK, so the problem is now either before or AT V4.

                            Look at grid pin 7 and R48 of V4. See PREOUT nearby? That connects to the Preamp Out jack. SO, is the noise present there?
                            Yes, I just ran a cable from PREOUT into another amps fx return and the noise came through.
                            I should've thought to check that last night. The noise seems to get worse the longer the amp is on and the tubes warm up.

                            Comment


                            • #15
                              And I bet if you pull V4, the noise still comes out the preamp jack?
                              Education is what you're left with after you have forgotten what you have learned.

                              Comment

                              Working...
                              X