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Laney TT50H No Outout

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  • #76
    12VDC across that resistor makes approx. 1.5 Watts. Not sure what the resistor rating is, but I doubt it is a 2W. And you are only at 40V so far, so it will go much higher.
    The 12VDC should not be there. It should be around 6.5VAC maximum at full line voltage if schematic is correct. Something is still putting DC on the heater line.
    Remove tubes one at a time to see if you can make that voltage disappear.
    "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

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    • #77
      And maake sure nothing on the power tube sockets is leaning over and touching the heater pins.
      Education is what you're left with after you have forgotten what you have learned.

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      • #78
        Originally posted by g1 View Post
        12VDC across that resistor makes approx. 1.5 Watts. Not sure what the resistor rating is, but I doubt it is a 2W. And you are only at 40V so far, so it will go much higher.
        The 12VDC should not be there. It should be around 6.5VAC maximum at full line voltage if schematic is correct. Something is still putting DC on the heater line.
        Remove tubes one at a time to see if you can make that voltage disappear.
        Removed all tubes one at a time, and while doing that, I ran variac up to 91 volts and can see red glow thru hum balance adjustment. This is the small circle I first saw when I thought maybe a capacitor was heating up. Checking dcv on two(2) of the three(3) pins on him balance pot and it's going up to 328v when at 91v on variac, then the red glow and I shut it down. Reinstalled all tubes and tried it again and got same results on hum balance pot, 328v @ 91v on variac, 2 of 3 pins, then red glow in hum adjustment hole. Original hum balance pot melted and now the replacement is also heating up.

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        • #79
          " Checking dcv on two(2) of the three(3) pins on him balance pot and it's going up to 328v when at 91v on variac, then the red glow and I shut it down."
          Wow.
          328 Vdc on the heater circuit!


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          • #80
            It seemed there was no problem with anything involved with the heaters until you replaced C37. That is when R52 and the hum balance pot started to burn.
            Triple check your work looking for any solder bridges, bent tube socket pins, etc. Also check both sides of all tube sockets for any signs of arcing (carbon).
            You might even want to remove C37 and check underneath it. I had a Vox AC15 in where they ran a heater trace under the filter cap. The trace arced to the cap lead, but you couldn't see it til the cap was removed.

            This is a double sided circuit board, so there are a lot more hidden areas.
            "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


            • #81
              And please please please stop thinking of the variac as a contest. It isn't intended to be turned up until something smokes. We turn it up while we watch mains current. If we see that rising, BACK OFF.

              Clearly your B+ is shorted to the heaters.
              Education is what you're left with after you have forgotten what you have learned.

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              • #82
                Originally posted by g1 View Post
                It seemed there was no problem with anything involved with the heaters until you replaced C37. That is when R52 and the hum balance pot started to burn.
                Triple check your work looking for any solder bridges, bent tube socket pins, etc. Also check both sides of all tube sockets for any signs of arcing (carbon).
                You might even want to remove C37 and check underneath it. I had a Vox AC15 in where they ran a heater trace under the filter cap. The trace arced to the cap lead, but you couldn't see it til the cap was removed.

                This is a double sided circuit board, so there are a lot more hidden areas.
                Removed C37 and was able to take variac to 104v(400vdc on board) without any voltage reading on hum balance pot or R52. Didn't find anything under C37. Put some solder on two(2) spots showing copper on the board near V5. Nothing else obvious that I see.

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                • #83
                  So with C37 installed, there is over 300VDC on the hum balance pot, but with C37 removed, that DC is not there?
                  "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


                  • #84
                    Originally posted by g1 View Post
                    So with C37 installed, there is over 300VDC on the hum balance pot, but with C37 removed, that DC is not there?
                    That is correct. No red glow, no smoke, and no voltage on either component. R52 still reads 100 ohms, and hum balance pot did not melt like original one did.

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                    • #85
                      This makes no sense to me. Even if the new C37 was faulty and shorted, it should have no connection to the heater circuit whatsoever. And if there is some kind of board fault, it should be there whether the cap is installed or not.

                      Can you post pics of where the cap goes, with cap removed? Both sides of circuit board.
                      "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


                      • #86
                        Originally posted by g1 View Post
                        This makes no sense to me. Even if the new C37 was faulty and shorted, it should have no connection to the heater circuit whatsoever. And if there is some kind of board fault, it should be there whether the cap is installed or not.

                        Can you post pics of where the cap goes, with cap removed? Both sides of circuit board.
                        Photos of both sides of board. Traces are not in great shape, but I do have continuity down line in both directions when C37 is soldered in place.

                        Comment


                        • #87
                          Originally posted by g1 View Post
                          This makes no sense to me. Even if the new C37 was faulty and shorted, it should have no connection to the heater circuit whatsoever. And if there is some kind of board fault, it should be there whether the cap is installed or not.

                          Can you post pics of where the cap goes, with cap removed? Both sides of circuit board.
                          What do you make of the board photos?

                          Comment


                          • #88
                            Originally posted by ca7922303 View Post

                            What do you make of the board photos?
                            Nothing suspicious looking there. And there are only traces on one side for that cap. Follow those traces to see if there are any accidental solder bridges anywhere.
                            I don't see any reason why that C37 cap being in place would cause the DC on the hum balance pot (if it's not there without the cap).
                            You might want to verify again that the DC on the hum pot is gone with cap out and returns with cap in.
                            "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

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