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  • #61
    Originally posted by g1 View Post
    I see an R52 connected to the hum balance pot. Did you see it burn or could it have burnt before? Doesn't seem to be anything that would be related to C37.
    Are power tubes installed? Any chance one of them has the locater pin broken off in the center of the base of the tube?
    Originally posted by g1 View Post
    I see an R52 connected to the hum balance pot. Did you see it burn or could it have burnt before? Doesn't seem to be anything that would be related to C37.
    Are power tubes installed? Any chance one of them has the locater pin broken off in the center of the base of the tube?
    Also, hum balance pot ps2 looks a little melted compared to ps1/ps3.

    Comment


    • #62
      Originally posted by g1 View Post
      I see an R52 connected to the hum balance pot. Did you see it burn or could it have burnt before? Doesn't seem to be anything that would be related to C37.
      Are power tubes installed? Any chance one of them has the locater pin broken off in the center of the base of the tube?
      Reinstalled new R52. Should I try to power on without any tubes(power & preamp)?

      Comment


      • #63
        Originally posted by ca7922303 View Post

        Reinstalled new R52. Should I try to power on without any tubes(power & preamp)?
        Originally posted by ca7922303 View Post
        I actually saw what looked like the size of a cap light up when I turned it on. C2/C7 area of board. I've checked both el34s and they both have the locater pin glued back on.
        Did you find something in that C2/C7 area? Or is that where R52 is? We don't have a board layout so without pictures we have no idea what is in that area.

        "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


        • #64
          Originally posted by g1 View Post

          Did you find something in that C2/C7 area? Or is that where R52 is? We don't have a board layout so without pictures we have no idea what is in that area.
          Yes, that is where R52 is near. Maybe it lit up C2 or c7 cause it appeared to be a small circle glowing thru the board(components face down).

          Comment


          • #65
            Then replace R52, and I would try it with just the preamp tubes. Do you have other power tubes to try? If someone glued the locator pin in the wrong position that could be the problem. Or are these power tubes the known working power tubes you mentioned at the start?
            "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


            • #66
              Originally posted by g1 View Post
              Then replace R52, and I would try it with just the preamp tubes. Do you have other power tubes to try? If someone glued the locator pin in the wrong position that could be the problem. Or are these power tubes the known working power tubes you mentioned at the start?
              Yes, these are the original el34s that I did get a good power amp signal thru another amp. Will reinstall board and test with preamp tubes only first.

              Comment


              • #67
                Originally posted by g1 View Post
                Then replace R52, and I would try it with just the preamp tubes. Do you have other power tubes to try? If someone glued the locator pin in the wrong position that could be the problem. Or are these power tubes the known working power tubes you mentioned at the start?
                Ok, it m ready to test without power tubes installed. Am I able to power on and test without power tubes and without a load? I should know this but can't find anywhere on internet where both are uninstalled for testing? Thanks.

                Comment


                • #68
                  Originally posted by ca7922303 View Post

                  Ok, it m ready to test without power tubes installed. Am I able to power on and test without power tubes and without a load? I should know this but can't find anywhere on internet where both are uninstalled for testing? Thanks.
                  Yes, if power tubes are removed, it can be run without a load.
                  Without the power tubes installed the main supply voltage will rise. So check that the big filter caps (C22, C23) are not getting more than their rated voltage. This is the only problem that may arise when testing with power tubes removed. In this case it looks like C22 and C23 are rated for 500V. So as long as the voltage on them doesn't go over 500V you are ok to test with tubes removed.
                  "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


                  • #69
                    Originally posted by g1 View Post

                    Yes, if power tubes are removed, it can be run without a load.
                    Without the power tubes installed the main supply voltage will rise. So check that the big filter caps (C22, C23) are not getting more than their rated voltage. This is the only problem that may arise when testing with power tubes removed. In this case it looks like C22 and C23 are rated for 500V. So as long as the voltage on them doesn't go over 500V you are ok to test with tubes removed.
                    With power tubes removed and no load, variac on about 60v, power on, got 156vdc @ SCR, then smoke(R52 burnt again).

                    Comment


                    • #70
                      Originally posted by g1 View Post

                      Yes, if power tubes are removed, it can be run without a load.
                      Without the power tubes installed the main supply voltage will rise. So check that the big filter caps (C22, C23) are not getting more than their rated voltage. This is the only problem that may arise when testing with power tubes removed. In this case it looks like C22 and C23 are rated for 500V. So as long as the voltage on them doesn't go over 500V you are ok to test with tubes removed.
                      Photos of component side of board and ps1, ps2, ps3.

                      Comment


                      • #71
                        I suspect V5 has a heater to cathode short (bad tube).
                        It is a cathode follower circuit. The schematic has an error showing a resistor R20. There is no resistor, V5 pin1 goes straight to C37. That is what you had found earlier when you repaired the connection between C37 and V5 pin1.

                        Replace R52. If PS2 is bad it will need to be replaced as well. Bring it up on the variac with all tubes installed except V5. Keep checking that R52 is not overheating.
                        Remember with power tubes installed you will need the load connected.
                        "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


                        • #72
                          Originally posted by g1 View Post
                          I suspect V5 has a heater to cathode short (bad tube).
                          It is a cathode follower circuit. The schematic has an error showing a resistor R20. There is no resistor, V5 pin1 goes straight to C37. That is what you had found earlier when you repaired the connection between C37 and V5 pin1.

                          Replace R52. If PS2 is bad it will need to be replaced as well. Bring it up on the variac with all tubes installed except V5. Keep checking that R52 is not overheating.
                          Remember with power tubes installed you will need the load connected.
                          Replaced R52, ordered a 1k bias pot from tube depot(3-5 days delivery). Also need a piggyback push button switch (one broke on me). Digikey says CIT doesn't show one now(there is a CIT one on internet previously). Not finding one at mouser either. Maybe someone has a link?

                          Comment


                          • #73
                            Originally posted by g1 View Post
                            I suspect V5 has a heater to cathode short (bad tube).
                            It is a cathode follower circuit. The schematic has an error showing a resistor R20. There is no resistor, V5 pin1 goes straight to C37. That is what you had found earlier when you repaired the connection between C37 and V5 pin1.

                            Replace R52. If PS2 is bad it will need to be replaced as well. Bring it up on the variac with all tubes installed except V5. Keep checking that R52 is not overheating.
                            Remember with power tubes installed you will need the load connected.
                            Installed ps2, all tubes installed except V5, variac up to 60v, then getting smoke near R52. R52 is not burnt and still reads 100 ohms.

                            Comment


                            • #74
                              You will have to verify whether the smoke is coming from R52, or something else nearby. Measure voltage across R52, check both DC and AC volts. Variac up to 60V, same as when you noticed smoke.
                              "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


                              • #75
                                Originally posted by g1 View Post
                                You will have to verify whether the smoke is coming from R52, or something else nearby. Measure voltage across R52, check both DC and AC volts. Variac up to 60V, same as when you noticed smoke.
                                Ran variac up to 40v before smoke occurred, 12vdc/0.03vac. R52 still not burnt and @ 100 ohms

                                Comment

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