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Another Blues Jr. Crackling Problem

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  • #16
    Unfortunately the silver mica cap isn’t the problem. I replaced with a similar cap but still have the noise.

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    • #17
      I would pin point the source of the noise.
      Obviously the valve has been checked/swapped out for a known quiet one.
      If the Master controls the noise and the treble controls it as well, the source is V1 or its components.
      Does the vol control control the noise ... if it does, you have an issue with V1 b if not look around V1 a.
      Replace the anode load resistor; 100k 1/2W.

      Let us know how you get on.
      Support for Fender, Laney, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk
      If you can't fix it, I probably can.

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      • #18
        Originally posted by Jon Snell View Post
        I would pin point the source of the noise.
        Obviously the valve has been checked/swapped out for a known quiet one.
        If the Master controls the noise and the treble controls it as well, the source is V1 or its components.
        Does the vol control control the noise ... if it does, you have an issue with V1 b if not look around V1 a.
        Replace the anode load resistor; 100k 1/2W.

        Let us know how you get on.

        R8 will be the first thing I look at tomorrow. The tubes were all new and I had switched V1 with a couple others. Only the MV & to some lesser extent the Treble control the volume of the noise. Would you be so kind to briefly explain your thought process to make that conclusion. It would be of real learning value. I try to pick up something new everyday on this amazing hobby.

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        • #19
          I checked R8 & it was fine but now I've lost all sound...jeez, what next. How do I go about tracking where sound was lost without a scope?

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          • #20
            Originally posted by Perkinsman View Post
            I checked R8 & it was fine but now I've lost all sound...jeez, what next. How do I go about tracking where sound was lost without a scope?
            signal tracer.
            nosaj
            soldering stuff that's broken, breaking stuff that works, Yeah!

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            • #21
              Perhaps R8 has a bad solder connection on the board and you revealed the connection issue while checking the resistor. Check plate voltage right at the tube to see if it's getting there. Could also be bad ribbon cable connections.
              "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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              • #22
                In tubes, "new" is not the same thing as "good". You have all new tubes, but you said you tried various tubes in V1. Did you trry different tubes in V2?

                When looking at V2, don't forget R16, R17. Without the tube, there is no current through them, so WITH the tube they could surely be involved.
                Education is what you're left with after you have forgotten what you have learned.

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                • #23
                  Thanks gents, I'll be looking atthis in the morning.

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                  • #24
                    R8, R16 & R17 were all good but when I looked at V5 solders, I can see that pins 6 & 7 are loose. I could see a very tiny spark next to pin 6, which as you can see has lost contact with the board. Pin 6 doesn’t have any function so does it matter whether it lost connection? The spark is actually from the trace of pin 4 which passes along side of pin 6. I may have scraped a tiny, little bit of the trace. Can I spray some conformal coating on it & let it dry & power it back on? Pin 7 had lost it’s trace but I repaired it.
                    Attached Files

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                    • #25
                      I'm not sure I'm understanding. Was the arcing a connection that was supposed to be there but wasn't? Or, was the arcing across traces that were not supposed to be connected? If a tube pin doesn't connect to anything, then it's not important that it be soldered in. If traces are arcing across each other, I will sometimes take an x-acto knife and carve a groove between the traces for better isolation. You can spray conformal coating if you like, but as long as it's not arcing, I don't think it's necessary.
                      "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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                      • #26
                        If the arc is between pin 6 and something, and pin 6 does nothing in the circuit, suck the solder off it. That will make it physically smaller and thus farther away from the trace it arcs to.

                        I would grind away some of the pc board material in the space between pin 6 and the trace, just in case it may have a tiny carbonized trail.
                        Education is what you're left with after you have forgotten what you have learned.

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                        • #27
                          Originally posted by The Dude View Post
                          I'm not sure I'm understanding. Was the arcing a connection that was supposed to be there but wasn't? Or, was the arcing across traces that were not supposed to be connected? If a tube pin doesn't connect to anything, then it's not important that it be soldered in. If traces are arcing across each other, I will sometimes take an x-acto knife and carve a groove between the traces for better isolation. You can spray conformal coating if you like, but as long as it's not arcing, I don't think it's necessary.
                          No, if you look at the picture, the arcing was just above pin 6, which is the trace for pin 4. It's not supposed to be connected. I think I may have scraped a tiny bit into trace 4 when I was initially trying to repair pin 6. Anyway, I sprayed some conformal on it and it seems to have stopped arcing. On V4, pin 7, there was also a small arc from the solder to the board after repairing the trace. That also seemed to stop when I sprayed the coating on it.

                          However, when I wiggle V4, theres some crackle, pop noise. I tightened the pins and it helped a little but still can't get audio from the amp.

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                          • #28
                            Originally posted by Enzo View Post
                            If the arc is between pin 6 and something, and pin 6 does nothing in the circuit, suck the solder off it. That will make it physically smaller and thus farther away from the trace it arcs to.

                            I would grind away some of the pc board material in the space between pin 6 and the trace, just in case it may have a tiny carbonized trail.
                            I sucked the solder away from pin 6 on both V5 & V4, & sprayed conformal and it stopped the arcing....still don't have audio from the amp.

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                            • #29
                              Originally posted by nosaj View Post
                              signal tracer.
                              nosaj
                              I'd like to build this today, thanks. After watching the video, I can see that the signal generator gets plugged into the amp via 1/4" jack but it was unclear where the audio probe gets plugged into? Another input on the amp? What if the amp only has one input?

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                              • #30
                                An arc either goes someplace it shouldn't, or it completes a circuit where it should. If pin 6 arcs to the trace from pin 4, that is the first type. If we solder a pin and it arcs by itself, that would likely be the latter. If we solder a pin to a pad, say, and the pad has cracked free from the trace that trails off, then we can arc between the pad and the trace end. Or maybe the blob of solder on the pin didn't actually wet to the pad, so that arcs.

                                Paint hides problems, it doesn't fix them. Pin 7 is your plate, and if we are in that second scenario, your paint MIGHT have isolated the plate, leaving only one side of the push pull. I said MIGHT.

                                In any case, just one working power tube would still pass signal. SO you have no audio. Isolate the problem. Turn up the reverb and shake the amp to crash the springs. Have the master volume up. Does that reverb noise come out? Is the amp out of the cab and no reverb pan? Just touch the tip of the return cable to make a signal.

                                Are ALL heaters in all five tubes glowing? Is there B+ on pins 1 and 6 of each 12AX7? And on pons 7 and 9 of the power tubes? Wiggle the ribbon cables, aany noise? And with signal applied, does signal momentarily appear?

                                Signal to input, trace it with scope or signal tracer. Got it at each of those pins 1 and 6?
                                Education is what you're left with after you have forgotten what you have learned.

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