Announcement

Collapse
No announcement yet.

Bad Cat Black Cat 30R Low B+

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

  • #61
    What about the pin2 grid voltages?
    "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


    • #62
      Originally posted by g1 View Post
      What about the pin2 grid voltages?
      They all show roughly the same, initially they were around 6.7V but appeared to be steadily increasing so when I shut it off after two minutes or so it had climbed to around 7.3V.

      Comment


      • #63
        There is no salvation from the horror.
        Let someone to try draw right schematic.

        Click image for larger version

Name:	a032.gif
Views:	68
Size:	15.4 KB
ID:	911596
        It's All Over Now

        Comment


        • #64
          Originally posted by bobloblaws View Post

          They all show roughly the same, initially they were around 6.7V but appeared to be steadily increasing so when I shut it off after two minutes or so it had climbed to around 7.3V.
          Should be 0V on cathode bias, right? Coupling cap? I'll look into it.

          Comment


          • #65
            Originally posted by vintagekiki View Post
            There is no salvation from the horror.
            Let someone to try draw right schematic.

            Click image for larger version

Name:	a032.gif
Views:	68
Size:	15.4 KB
ID:	911596
            I'll throw you a bone. This is what I've completed so far.

            Click image for larger version

Name:	BC30R.jpg
Views:	135
Size:	472.0 KB
ID:	911600

            Comment


            • #66
              Originally posted by bobloblaws View Post

              I'll throw you a bone. This is what I've completed so far.

              Click image for larger version

Name:	BC30R.jpg
Views:	135
Size:	472.0 KB
ID:	911600
              There's a mistake in the LTP. The cathode bias resistor is on the wrong side of the 2 x 1M grid leak resistors
              Building a better world (one tube amp at a time)

              "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

              Comment


              • #67
                Originally posted by tubeswell View Post

                There's a mistake in the LTP. The cathode bias resistor is on the wrong side of the 2 x 1M grid leak resistors
                Good catch! Here it is revised.

                Generally speaking, this is obviously still very much a work in progress.

                Click image for larger version

Name:	BC30R.jpg
Views:	129
Size:	425.0 KB
ID:	911613​​

                Comment


                • #68
                  Originally posted by bobloblaws View Post
                  I'll throw you a bone. This is what I've completed so far.
                  With your permission a little help to a friend.
                  If it's easier for you, look at the layout
                  https://music-electronics-forum.com/filedata/fetch?id=911249

                  Click image for larger version

Name:	image_51497.jpg
Views:	129
Size:	529.2 KB
ID:	911615
                  It's All Over Now

                  Comment


                  • #69
                    Originally posted by vintagekiki View Post
                    With your permission a little help to a friend.
                    If it's easier for you, look at the layout
                    https://music-electronics-forum.com/filedata/fetch?id=911249

                    Click image for larger version

Name:	image_51497.jpg
Views:	129
Size:	529.2 KB
ID:	911615
                    That may come in handy, thank you.

                    Comment


                    • vintagekiki
                      vintagekiki commented
                      Editing a comment
                      I'm here to help

                  • #70
                    Originally posted by bobloblaws View Post

                    Good catch! Here it is revised.

                    Generally speaking, this is obviously still very much a work in progress.

                    Click image for larger version

Name:	BC30R.jpg
Views:	129
Size:	425.0 KB
ID:	911613​​
                    PI master grid and slave triode grid is still confused
                    ​​​​​​​
                    Click image for larger version

Name:	Still confused.jpg
Views:	68
Size:	439.5 KB
ID:	911620
                    Building a better world (one tube amp at a time)

                    "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

                    Comment


                    • #71
                      Originally posted by tubeswell View Post
                      PI master grid and slave triode grid is still confused
                      Matchless dc30 pwr
                      http://www.prowessamplifiers.com/schematics/post/matchless_dc30.pdf
                      It's All Over Now

                      Comment


                      • #72
                        Originally posted by vintagekiki View Post
                        And its clearly still wrong ...

                        The tail resistor should be grounded (or ground referenced to an NFB loop). Instead the LTP cathode is grounded (the way its drawn in the OP's schematic)
                        Building a better world (one tube amp at a time)

                        "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

                        Comment


                        • #73
                          Originally posted by bobloblaws View Post

                          They all show roughly the same, initially they were around 6.7V but appeared to be steadily increasing so when I shut it off after two minutes or so it had climbed to around 7.3V.
                          Ok, now we're getting closer.
                          So we have unwanted positive grid voltages. There's no doubt that this causes the high cathode currents and low B+.

                          Please proceed as follows:

                          1) Measure socket pin 2 voltages with all EL84s pulled.
                          2) Make sure that the junction of the two 220k grid leaks is well grounded (0VDC).
                          3) Lift both 47nF coupling caps and remeasure socket pin 2 voltages.
                          - Own Opinions Only -

                          Comment


                          • #74
                            Originally posted by tubeswell View Post
                            And its clearly still wrong ...

                            The tail resistor should be grounded (or ground referenced to an NFB loop). Instead the LTP cathode is grounded (the way its drawn in the OP's schematic)
                            Schematics Matchless dc30 pwr is correct.
                            http://www.prowessamplifiers.com/schematics/post/matchless_dc30.pdf

                            Compare
                            http://dealers.korgusa.com/svcfiles/ac30p1.pdf

                            DC30 and AC30 do not have NFB
                            It's All Over Now

                            Comment


                            • #75
                              I think the 100k is the tail resistor and is grounded together with the upper PI input (assuming there is no NFB).

                              (Using a continuity tester and/or Ohmmeter can be a big help in finding hidden connections.)
                              Last edited by Helmholtz; 08-21-2020, 04:00 PM.
                              - Own Opinions Only -

                              Comment

                              Working...
                              X