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  • Engl Powerball interesting problem.

    So I have a powerball here in the shop that the guy was complaining about not getting any sound. I found that the 47uf 500v cap was leaking, and replaced it, now it will come on and not make horrible sounds, but will not do anything when I plug a guitar in. I can tap on all the tubes and hear sound coming out of it. I can tap on the chassis and hear it come out of the speakers, but nothing out of the input. I checked with a meter to make sure the input jack was good, and checked grounds all around it.

    I remember this happening in an old fender hot rod deville, but it had a trs jack, not just a TS..
    Any ideas?

    Thanks!
    D

  • #2
    If you have indeed isolated the problem to the input jack then it should be gravy from here. Never rule out coincidence. If you've determined, and are correct, that the amp is generating sound and the input jack is functional then there happens to be a problem with your guitar or cable.

    You could narrow down the problem by disconnecting the hot lead on the input jack and injecting a signal straight to the first triodes grid. Be certain to provide a 0V reference for the grid or the tube will "run away". If injecting a signal straight to the grid works then the input jack must be the problem. If you get nothing (no hum from handling, pops or clicks when touching the grid with implements) then the problem is, or ahead of the first triodes grid.
    "Take two placebos, works twice as well." Enzo

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "If you're not interested in opinions and the experience of others, why even start a thread?
    You can't just expect consent." Helmholtz

    Comment


    • #3
      I can get a couple pops when I'm checking voltage across the tubes. I get them going all the way back to v8, but before that I get nothing..
      Its kind of weird on the schematic, v1-4 are the power tubes, v8 is the phase inverter.
      when I turn the knobs on the amp I dont hear the characteristic swell, say like white noise on the gain channel getting louder, I just hear noise when either I tap a tube or the chassis..

      Comment


      • #4
        OK, I downloaded the schem. But that's no assurance that it matches yours. There were a couple of different schems. I see that amp has the effects loop switching jacks. Try plugging directly into the effects return. Anything? How about a jumper in the effects loop? Seems silly, I know. You'd be surprised how often those jacks short, get dirty or otherwise cause problems.
        "Take two placebos, works twice as well." Enzo

        "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

        "If you're not interested in opinions and the experience of others, why even start a thread?
        You can't just expect consent." Helmholtz

        Comment


        • #5
          I plugged into the effects return and get nothing. If I put it in the regular input and crank the volumes all the way up, I can hear it ever so slightly..

          Comment


          • #6
            Then you do indeed only have function from the PI and power tubes. Are all the preamp tubes lighting up? Do check voltages at all pins of V7 and re post please.
            "Take two placebos, works twice as well." Enzo

            "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

            "If you're not interested in opinions and the experience of others, why even start a thread?
            You can't just expect consent." Helmholtz

            Comment


            • #7
              When you go in the FX return jack, the balance pot and masters are still in circuit, so make sure they are turned up.
              Also, the standby appears to only lift the power tubes cathodes, make sure they are grounded when the switch is closed.
              Originally posted by Enzo
              I have a sign in my shop that says, "Never think up reasons not to check something."


              Comment


              • #8
                Good call on the control settings. I do think the power tubes are conducting because there is SOME sound back to the PI. The small signal from the input jack is probably power supply or capacitive coupling. That would mean that some of the amp behind the problem is working. Probably most of the preamp if there is enough voltage gain to couple an audible signal without a signal path. I think we'll find the problem localized to V7 or it's associated circuitry. It's just a hunch though since there isn't enough information yet to isolate the problem. If the effects loop has ever been in service, those jacks could still be a problem. Chincey ones fail open and board mounted ones can even break the pads off the board.
                "Take two placebos, works twice as well." Enzo

                "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                "If you're not interested in opinions and the experience of others, why even start a thread?
                You can't just expect consent." Helmholtz

                Comment


                • #9
                  Is this the schematic you are working from? http://music-electronics-forum.com/a...-powerball.pdf
                  Originally posted by Enzo
                  I have a sign in my shop that says, "Never think up reasons not to check something."


                  Comment


                  • #10
                    Yes, that is the schematic I'm working from too, and it seems to correspond well with this one.
                    V7 voltages are ... weird... I think.
                    1- -.8v
                    2- -.4v
                    3- 38mv
                    4- 5.6mv
                    5- 5.6mv
                    6- 228v
                    7- 1.1mv
                    8- 1.6v
                    9- 6.8v

                    I did check the jacks on the effects loop with a multimeter, and checked for continuity between the next point in the line where they return, and they all check out fine, and I also cleaned them thoroughly to be sure.

                    Also, thank you guys so much for the help! I definately need to get on here more and help spread the knowledge
                    Below is a small rant:
                    That being said above, I really hate when manufacturers make it almost impossible to work on their gear. I have to unsolder the entire power supply, the PT, the OT, the input jack, and the heaters, and the stupid LED's for the power tubes just to pull the board out and visually inspect components... I miss the days where manufacturers made things to be serviced

                    Comment


                    • #11
                      Originally posted by DizzyD View Post
                      Yes, that is the schematic I'm working from too, and it seems to correspond well with this one.
                      V7 voltages are ... weird... I think.
                      1- -.8v
                      2- -.4v
                      3- 38mv
                      4- 5.6mv
                      5- 5.6mv
                      6- 228v
                      7- 1.1mv
                      8- 1.6v
                      9- 6.8v
                      There is no voltage on pin 1. Check the plate resistor that is connected to it to see if it has gone open circuit or has come unsoldered.

                      Comment


                      • #12
                        Yeah, I thought about that after I posted.. 100k resistor thats supposed to go there is not reading anything...
                        Guess its a trip to radio shack tomorrow!

                        Comment


                        • #13
                          Did you remove the resistor for testing? This could be important. Because if you didn't the test points you chose could point to a problem other than the resistor. I'm not saying the resistor isn't bad. But they are spec'd 1W on the schem. That being the case I think it's more likely you have a broken pad on the board from the board mount tube socket, a burned trace for that power supply node or some other fault in the voltage path for that node.

                          Did you check voltages on any other tubes? You should.

                          Sorry the amp is such a PITA to work on. I DO know how it is.
                          "Take two placebos, works twice as well." Enzo

                          "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                          "If you're not interested in opinions and the experience of others, why even start a thread?
                          You can't just expect consent." Helmholtz

                          Comment


                          • #14
                            Well, Bill was right, the 100k resistor going into V1 was shorted open. Popped a new one of them in and the amp is as loud as new

                            Thank you guys for all the help!
                            Now if I can just figure out where this missing screw goes

                            Comment


                            • #15
                              Excellent. I think everyone here did a good job on this one. It's actually rare to have a new poster step in and actually listen, follow advice and provide the requested data. So kudos all around. But a question remains...

                              Why did the circuit blow a 1W plate resistor!?! That shouldn't happen outside of a gross failure. It's actually pretty rare to have a resistor be so poor that it'll spontaneously pop in a circuit designed for one quarter it's spec. Rare as in I've never seen it happen. So why did it pop? I have a couple of concearns. And they should be addressed to avoid a future failure. Possibilities, in order of likelihood are:

                              Loose or dirty socket slots or oxidized tube pins. If the amp has sat awhile or been stored in less than ideal conditions there may be a contact issue between the tube and it's socket. This may have caused the tube to lose bias and draw excessive current. Fix by cleaning with DeOxit and re tensioning the metal contacts in the socket.

                              Broken board pad or trace or cold solder joint at, or relating to that tube socket. Intermittent and causing the same problem as a bad socket. Detect by wiggling the tube while the amp is operating and poking the components (with a wooden stick) on the board connected to it. If poking the components causes faults in operation then you've found the fault. If wiggling the tube causes intermittent faults in operation you may have a cold joint or lifted pad right at the socket. If you hear a scraping, static like sound it's more likely dirty pin contacts.

                              Bad tube. Causing??? I've seen bad tubes do a lot of weird things.
                              "Take two placebos, works twice as well." Enzo

                              "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                              "If you're not interested in opinions and the experience of others, why even start a thread?
                              You can't just expect consent." Helmholtz

                              Comment

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