Announcement

Collapse
No announcement yet.

Gretsch Fury Reverb issue

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    What is the voltage at pin9 of the 6973? If you have 388VDC there, that is close enough. It does not mean the transformer is bad.
    What is the voltage at pin 7?
    "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


    • #17
      Across means one end to the other. If you have 388v ACROSS the primary, that would suggest 388 on one end and zero on the other. If you have about 388v to ground from each end, that is very different.
      Education is what you're left with after you have forgotten what you have learned.

      Comment


      • #18
        I think he is talking about the 500 ohm resistors now.

        Comment


        • #19
          Originally posted by 52 Bill View Post
          I think he is talking about the 500 ohm resistors now.
          Yes, there is actually 402v across those resistors (there is no voltage at first, but then it comes through, maybe as the amp warms up)

          There is no voltage across the primary leads to the reverb driver (pin 2 red, pin 2 blue) and no voltage on pin 7 of the 6973.

          Comment


          • #20
            Originally posted by dc74 View Post
            Yes, there is actually 402v across those resistors (there is no voltage at first, but then it comes through, maybe as the amp warms up)

            There is no voltage across the primary leads to the reverb driver (pin 2 red, pin 2 blue) and no voltage on pin 7 of the 6973.
            The readings you report are not consistent. Do this
            1) Set meter to DCV
            2) Clip black lead to ground and leave it there
            3) Report the reading with the red lead on the +ve end of C2
            4) Report the reading with the red lead on the +ve end of C5A
            5) Report the reading with the read lead on pin of 9 of V4
            6) Report the reading with the read lead on pin of 8 of V4
            7) Report the reading with the read lead on pin of 7 of V4
            Experience is something you get, just after you really needed it.

            Comment


            • #21
              3) Report the reading with the red lead on the +ve end of C2 - 406 vdc
              4) Report the reading with the red lead on the +ve end of C5A -1.8 vdc
              5) Report the reading with the read lead on pin of 9 of V4 - 1.8 vdc
              6) Report the reading with the read lead on pin of 8 of V4 - 1.75 vdc
              7) Report the reading with the read lead on pin of 7 of V4 - 0.1 mV

              Comment


              • #22
                Originally posted by dc74 View Post
                3) Report the reading with the red lead on the +ve end of C2 - 406 vdc
                4) Report the reading with the red lead on the +ve end of C5A -1.8 vdc
                5) Report the reading with the read lead on pin of 9 of V4 - 1.8 vdc
                6) Report the reading with the read lead on pin of 8 of V4 - 1.75 vdc
                7) Report the reading with the read lead on pin of 7 of V4 - 0.1 mV
                Seems the 500 Ohm resistor between C2 and C5A is defective (high resistance).
                Otherwise it would be dissipating around 330W (!).
                Last edited by Helmholtz; 02-08-2019, 04:22 PM.
                - Own Opinions Only -

                Comment


                • #23
                  I am thinking that is the case after running through the suggested checks...much thanks for that!

                  Comment


                  • #24
                    Replaced the 500 ohm Resistors and a few melty looking wires and now read:
                    Click image for larger version

Name:	old.jpg
Views:	1
Size:	103.5 KB
ID:	853043Click image for larger version

Name:	new.jpg
Views:	1
Size:	141.7 KB
ID:	853044

                    402v before resistors
                    359v after resistors

                    359v on Pin 2
                    14v on Pin 7
                    350v on Pin 9

                    No voltage on the green and black lines from the transformer...now I'm feeling more confident that's dead too.

                    Oddly I can crash the pan, and when I tested the front end of the resistors the "pop" that happened when I contacted the meter lead had reverb on it...

                    Comment


                    • #25
                      Originally posted by dc74 View Post
                      Replaced the 500 ohm Resistors and a few melty looking wires and now read:
                      [ATTACH=CONFIG]52483[/ATTACH][ATTACH=CONFIG]52484[/ATTACH]

                      402v before resistors
                      359v after resistors

                      359v on Pin 2
                      14v on Pin 7
                      350v on Pin 9

                      No voltage on the green and black lines from the transformer...now I'm feeling more confident that's dead too.

                      Oddly I can crash the pan, and when I tested the front end of the resistors the "pop" that happened when I contacted the meter lead had reverb on it...
                      Well, your new measurements show 9V across the rev. transformer primary. This could be OK and means continuity.
                      What is pin 2?
                      Voltage on pin 7 looks rather high. Please check 330 Ohm cathode resistor.

                      Can you identify green and black transformer wires in the schematic? I assume it's the secondary which shouldn't have any DC.

                      Please bend away all wires from the hot power resistors shown in the pictures.
                      Last edited by Helmholtz; 02-12-2019, 09:17 PM.
                      - Own Opinions Only -

                      Comment


                      • #26
                        Originally posted by Helmholtz View Post
                        Well, your new measurements show 9V across the rev. transformer primary. This could be OK and means continuity.
                        What is pin 2?
                        Voltage on pin 7 looks rather high. Please check 330 Ohm cathode resistor.

                        Can you identify green and black transformer wires in the schematic? I assume it's the secondary which shouldn't have any DC.

                        Please bend away all wires from the hot power resistors shown in the pictures.
                        The Left side picture was the original, I removed those resistors, and replaced them. I also replaced the wires which had melted to them. There is space now between those front leads and the new resistors (you can see in the right side picture).

                        Pin 9 is the Red Lead from the reverb Driver, Pin 2 is the Blue lead.

                        Pin 7 runs back to a buss bar with the black and green leads from the reverb driver and a series of caps.
                        Click image for larger version

Name:	6973.jpg
Views:	1
Size:	415.8 KB
ID:	853045

                        Comment


                        • #27
                          Pin 9 is the Red Lead from the reverb Driver, Pin 2 is the Blue lead.

                          Pin 7 runs back to a buss bar with the black and green leads from the reverb driver and a series of caps.

                          Sorry, not clear. Tube pin 2 is not connected internally, seems to be used as staging post only. I don't feel able to identify the wiring from the picture, looks like a mess to me.
                          But it seems that red and blue wires are rev. transformer primary while black and green wires are secondary (just as in Fenders). Given this, your voltage readings make sense - apart from the suspiciously high pin 7 voltage.
                          - Own Opinions Only -

                          Comment


                          • #28
                            The voltage drops across the 500 ohms resistors and the 330 ohm cathode resistor are consistent with a cathode current of about 42mA. OTOH the tube will be running at max dissipation. None of that will stop it working though. If the cathode bypass cap 25uF were bad it would lower the gain a little and reduce the reverb but not kill it.

                            Try this: Plug a speaker into the reverb footswitch jack and disconnect the tank input. You should get a decent volume out of the speaker. If that is OK tack a 25uf cap across the existing cathode bypass cap. If it's louder the existing cap was bad. If nothing or very quiet then the problem is earlier.
                            Experience is something you get, just after you really needed it.

                            Comment


                            • #29
                              There is 14vdc flowing off Pin 7 (of the 6973) into the cathode bypass cap, 13.58vdc flowing out of the cap and into the 330ohm resistor...then no voltage on the other side of the resistor...and and therefore no voltage after that to the secondary lead of the driver transformer...

                              Comment


                              • #30
                                Originally posted by dc74 View Post
                                There is 14vdc flowing off Pin 7 (of the 6973) into the cathode bypass cap, 13.58vdc flowing out of the cap and into the 330ohm resistor...then no voltage on the other side of the resistor...and and therefore no voltage after that to the secondary lead of the driver transformer...
                                Those are normal ( we already covered this IIRC). Try the tests in post #28.
                                Experience is something you get, just after you really needed it.

                                Comment

                                Working...
                                X