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70s Ampeg V4B Blows Fuses

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  • Originally posted by g1 View Post
    Under same conditions, measure DC volts at both sides of standby switch.
    SW4(9v/9v).

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    • Originally posted by g1 View Post
      Under same conditions, measure DC volts at both sides of standby switch.
      What do you make of those measurements and the diodes? Thanks.

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      • Try it with one probe on each side of the diode, black probe to cathode end (silver band).
        "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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        • Originally posted by g1 View Post
          Try it with one probe on each side of the diode, black probe to cathode end (silver band).
          D-1/D-2(-290v), D-3/D-4(-261v), D-5(-9.9v), D-6(-107v).

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          • It's just D5 I was wondering about, and I think that is normal but I'll double check mine tomorrow.
            How many of the tube heaters are not lit up? They can be hard to see sometimes so checking in the dark can help, also feel them for any heat.
            "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


            • Originally posted by g1 View Post
              It's just D5 I was wondering about, and I think that is normal but I'll double check mine tomorrow.
              How many of the tube heaters are not lit up? They can be hard to see sometimes so checking in the dark can help, also feel them for any heat.
              Checked power tubes in dark, had one(1) power tube not lighting or warming up. Thanks for your help.

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              • I'm not going back through 171 posts, but any chance that dark tube has the center plastic post broken off the base?
                Education is what you're left with after you have forgotten what you have learned.

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                • Originally posted by ca7922303 View Post
                  Thanks for your help.
                  Thank you for spin yourself.
                  Click image for larger version

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                  Who does not know and knows that he does not know - teach him Confucius)
                  Who knows and does not know that he knows - wake him Confucius)

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                  • Originally posted by Enzo View Post
                    I'm not going back through 171 posts, but any chance that dark tube has the center plastic post broken off the base?
                    Checked the bad tube socket with several different tubes, all had center plastic post intact.

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                    • Do checked several different tubes lighting or dark (not lighting)?
                      Who does not know and knows that he does not know - teach him Confucius)
                      Who knows and does not know that he knows - wake him Confucius)

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                      • Originally posted by vintagekiki View Post
                        Do checked several different tubes lighting or dark (not lighting)?
                        Only one(1) tube socket is not producing a lighted or warm tube. This socket has been tested with several known good tubes.

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                        • Originally posted by ca7922303 View Post
                          Only one(1) tube socket is not producing a lighted or warm tube. This socket has been tested with several known good tubes.
                          On a tube socket that is not producing a lighted or warm tube, check between pin 2 and pin 7 that there is a voltage of 6.3 VAC.
                          On the same tube socket check if there is soot between pin 2 and pin 3.
                          If the tube socket damaged, burned replace with a new socket.

                          https://drtube.com/datasheets/7027a-rca1959.pdf
                          Who does not know and knows that he does not know - teach him Confucius)
                          Who knows and does not know that he knows - wake him Confucius)

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                          • After you get that socket working, try this test again to see if power amp & supply are still basically working: https://music-electronics-forum.com/...556#post929556
                            "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


                            • Originally posted by vintagekiki View Post
                              On a tube socket that is not producing a lighted or warm tube, check between pin 2 and pin 7 that there is a voltage of 6.3 VAC.
                              On the same tube socket check if there is soot between pin 2 and pin 3.
                              If the tube socket damaged, burned replace with a new socket.

                              https://drtube.com/datasheets/7027a-rca1959.pdf
                              All four(4) power tube sockets measure 6.3vdc between pin#2 & pin#7. Not sure what soot between pin#2 and pin#3 means? Can you clarify? Thanks.

                              Comment


                              • Originally posted by g1 View Post
                                After you get that socket working, try this test again to see if power amp & supply are still basically working: https://music-electronics-forum.com/...556#post929556
                                Measuring vdc on all four(4) power tube sockets: #1(10.5mv), #2(28.5v), #3(586v), #4(596v), #5(-63v), #6(9mv), #7(104mv), #8(10mv on 1), 3 at -0.

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